Spirooxindoles, featuring a spiro ring fused at the 3-position of the oxindole core, have attracted considerable attention over the past decades owing to their unique structural properties and widespread occurrence in natural products [1-3]. In particular, molecules bearing a spiropyrrolidine oxindole skeleton often exhibit intriguing biological activities [4-6]. For example, as shown in Scheme 1, mitraphylline (compound Ⅰ), a spirooxindole alkaloid isolated from the leaves of Mitragyna speciosa, shows antiproliferative effects, while compounds Ⅱ and Ⅲ exhibit antibacterial and antitumor activities, respectively [7, 8]. In addition, these motifs find application in the synthesis of new ligands and catalysts [9]. In this regard, intense efforts have been devoted to their synthesis [2, 10-12]. Thus far, most synthetic methods have focused on the 1, 3-dipolar cycloaddition of azomethine ylides [13-17] and the intramolecular cyclization of preformed precursors [18-24]. Despite these advances, there is still a high demand for the exploration of new catalytic routes for the bimolecular assembly of spiropyrrolidine oxindoles.

Vinyl azides, featuring both alkene and azide motifs, are versatile building blocks in the divergent synthesis of various azaheterocycles [25, 26]. Moreover, diazo compounds have been widely employed as coupling partners in the annulation reaction. However, the cycloaddition of vinyl azides and diazo compounds has rarely been explored. Vinyl azides serve as two-atom partners in the reported Rh-catalyzed cyclopropanation [27] (Scheme 2a) and Cu-catalyzed [3+2] cycloaddition [28] (Scheme 2b) reactions. Following our previous studies on the azide chemistry [29-31] and cycloaddition reactions [32, 33], we directed our attention towards developing new cycloaddition reactions of vinyl azides and diazo compounds, in which vinyl azides may serve as three-atom synthons. Herein, we report a Rh(Ⅱ)-catalyzed [3+1+1] annulation of vinyl azides and 3-diazooxindoles, enabling the facile synthesis of spiropyrrolidine oxindoles (Scheme 2d). Coincidentally, while this work was underway, Katukojvala's group [34] reported the synthesis of functionalized 1-pyrrolines via a similar annulation of diazoenals and vinyl azides (Scheme 2c).

Commercially available reagents were used without further purification. Solvents were treated prior to use according to standard methods. All reactions were carried out under an argon atmosphere using standard Schlenk techniques or in an argon-filled glove box, unless otherwise noted. Column chromatography was carried out on silica gel (300–400 mesh) using a forced flow of eluent at a pressure of 0.3–0.5 bar. For thin-layer chromatography (TLC) experiments, silica gel GF254 was used and visualized by fluorescence quenching under UV light. NMR spectra were recorded on a Bruker 400 MHz NMR spectrometer in the solvents indicated below. The ¹H and ¹³C NMR chemical shifts were recorded in ppm downfield from the corresponding central peaks of CDCl₃ (7.26 and 77.16 ppm, respectively), used as the internal standard. Coupling constants (J) are reported in Hz and refer to apparent peak multiplications. The 3-diazooxindole and vinyl azide compounds were synthesized according to known literature procedures [35, 36].

Under argon atmosphere, dirhodium(Ⅱ) tetra(trifluoroacetate) (Rh₂(TFA)₄, 2.5 mol%) was added to a mixture of 3-diazooxindole 1 (0.3 mmol) and vinyl azide 2 (2.1 mmol) in 1, 2-dichloroethane (DCE, 3 mL). The mixture was stirred at 60 ℃ for 10 h until the substrate 1 was consumed. Then, the solvent was evaporated and the crude product was directly purified by flash column chromatography on silica gel (using petroleum ether/ethyl acetate as eluent) to give the desired product 3.

1-Methyl-5'-phenyl-3', 4'-dihydrospiro[indoline-3, 2'-pyrrol]-2-one (3aa): yellow solid; 65.7 mg; 79% yield; melting point (mp) 168–169 ℃; ¹H NMR (400 MHz, CDCl₃) δ 7.92–7.90 (m, 2H), 7.48–7.38 (m, 3H), 7.32 (td, J = 7.7, 1.3 Hz, 1H), 7.14 (dd, J = 7.3, 0.8 Hz, 1H), 7.06 (td, J = 7.5, 0.8 Hz, 1H), 6.87 (d, J = 7.8 Hz, 1H), 3.49 (ddd, J = 16.7, 9.6, 6.9 Hz, 1H), 3.37 (ddd, J = 17.0, 9.7, 5.2 Hz, 1H), 3.24 (s, 3H), 2.62 (ddd, J = 13.2, 9.6, 5.2 Hz, 1H), 2.29 (ddd, J = 13.2, 9.7, 6.9 Hz, 1H); ¹³C NMR (100 MHz, CDCl₃) δ 177.4, 177.3, 143.8, 133.9, 132.2, 131.2, 129.3, 128.5, 128.4, 123.7, 123.1, 108.4, 81.6, 36.9, 32.8, 26.5; high-resolution mass spectrometry (HRMS, Q-TOF, ESI) calcd for C₁₈H₁₇N₂O⁺ [M + H]⁺ 277.1335, found 277.1339.

1-Benzyl-5'-phenyl-3', 4'-dihydrospiro[indoline-3, 2'-pyrrol]-2-one (3ba): yellow solid; 93.0 mg; 88% yield; mp 137–138 ℃; ¹H NMR (400 MHz, CDCl₃) δ 7.94–7.91 (m, 2H), 7.47–7.40 (m, 3H), 7.35–7.29 (m, 4H), 7.27–7.23 (m, 1H), 7.19–7.13 (m, 2H), 7.02–6.98 (dd, J = 11.0, 4.0 Hz, 1H), 6.74 (d, J = 7.8 Hz, 1H), 5.02 (d, J = 15.7 Hz, 1H), 4.83 (d, J = 15.7 Hz, 1H), 3.50 (ddd, J = 16.8, 9.5, 7.2 Hz, 1H), 3.38 (ddd, J = 17.0, 9.7, 4.9 Hz, 1H), 2.67 (ddd, J = 13.4, 9.5, 4.9 Hz, 1H), 2.31 (ddd, J = 13.1, 9.7, 7.2 Hz, 1H); ¹³C NMR (100 MHz, CDCl₃) δ 177.57, 177.43, 142.87, 135.80, 133.86, 132.31, 131.22, 129.16, 128.87, 128.50, 128.40, 127.67, 127.41, 123.75, 123.17, 109.42, 81.62, 44.04, 36.84, 33.22; HRMS (Q-TOF, ESI) calcd for C₂₄H₂₁N₂O⁺ [M + H]⁺ 353.1648, found 353.1649.

1, 5'-Diphenyl-3', 4'-dihydrospiro[indoline-3, 2'-pyrrol]-2-one (3ca): yellow solid; 90.0 mg; 89% yield; mp 121–122 ℃; ¹H NMR (400 MHz, CDCl₃) δ 7.94–7.92 (m, 2H), 7.52–7.36 (m, 8H), 7.25–7.19 (m, 2H), 7.07 (t, J = 7.2 Hz, 1H), 6.88 (d, J = 7.9 Hz, 1H), 3.52–3.39 (m, 2H), 2.73 (ddd, J = 14.4, 9.5, 5.0 Hz, 1H), 2.37 (ddd, J = 13.1, 9.6, 7.2 Hz, 1H); ¹³C NMR (100 MHz, CDCl₃) δ 177.7, 176.6, 143.6, 134.5, 133.8, 132.1, 131.2, 129.6, 129.1, 128.5, 128.4, 128.0, 126.5, 124.0, 123.6, 109.7, 81.7, 36.9, 33.6; HRMS (Q-TOF, ESI) calcd for C₂₃H₁₉N₂O⁺ [M + H]⁺ 339.1492, found 339.1493.

1-Benzoyl-5'-phenyl-3', 4'-dihydrospiro[indoline-3, 2'-pyrrol]-2-one (3da): yellow solid; 100.5 mg; 91% yield; mp 129–130 ℃; ¹H NMR (400 MHz, CDCl₃) δ 7.95–7.89 (m, 3H), 7.77–7.75 (m, 2H), 7.57–7.53 (m, 1H), 7.49–7.39 (m, 6H), 7.24 (d, J = 3.7 Hz, 2H), 3.47–3.33 (m, 2H), 2.67 (ddd, J = 13.7, 8.4, 5.4 Hz, 1H), 2.38–2.30 (m, 1H); ¹³C NMR (100 MHz, CDCl₃) δ 178.0, 177.0, 169.5, 140.2, 134.2, 133.6, 132.9, 131.8, 131.5, 129.7, 129.5, 128.6, 128.5, 128.3, 125.7, 123.9, 115.5, 82.1, 37.0, 33.9; HRMS (Q-TOF, ESI) calcd for C₂₄H₁₉N₂O₂⁺ [M + H]⁺ 367.1441, found 367.1444.

5'-Phenyl-1-tosyl-3', 4'-dihydrospiro[indoline-3, 2'-pyrrol]-2-one (3ea): yellow solid; 112.3 mg; 90% yield; mp 70–71 ℃; ¹H NMR (400 MHz, CDCl₃) δ 8.00 (d, J = 8.4 Hz, 2H), 7.95 (d, J = 8.2 Hz, 1H), 7.84–7.82 (m, 2H), 7.48–7.45 (m, 1H), 7.41–7.36 (m, 3H), 7.31 (d, J = 8.1 Hz, 2H), 7.20–7.12 (m, 2H), 3.44–3.29 (m, 2H), 2.61 (ddd, J = 13.4, 8.8, 4.7 Hz, 1H), 2.41 (s, 3H), 2.21 (ddd, J = 13.4, 9.4, 8.3 Hz, 1H); ¹³C NMR (100 MHz, CDCl₃) δ 178.8, 175.4, 145.8, 139.0, 135.3, 133.4, 131.6, 131.2, 130.0, 129.9, 128.6, 128.5, 128.1, 125.5, 124.2, 113.9, 81.6, 36.6, 34.7, 21.8; HRMS (Q-TOF, ESI) calcd for C₂₄H₂₁N₂O₃S⁺ [M + H]⁺ 417.1267, found 417.1266.

1-(Methylsulfonyl)-5'-phenyl-3', 4'-dihydrospiro[indoline-3, 2'-pyrrol]-2-one (3fa): yellow solid; 76.0 mg; 74% yield; mp 163–164 ℃; ¹H NMR (400 MHz, CDCl₃) δ 7.91–7.89 (m, 2H), 7.81 (d, J = 8.2 Hz, 1H), 7.52–7.41 (dt, J = 25.9, 7.2 Hz, 3H), 7.38–7.34 (m, 1H), 7.23–7.17 (m, 2H), 3.51–3.36 (m, 5H), 2.72 (ddd, J = 13.8, 9.0, 5.0 Hz, 1H), 2.30 (ddd, J = 13.4, 9.4, 7.8 Hz, 1H); ¹³C NMR (100 MHz, CDCl₃) δ 178.8, 176.5, 138.8, 133.4, 131.7, 131.1, 130.0, 128.7, 128.5, 125.6, 124.3, 113.8, 81.7, 41.8, 36.8, 34.4; HRMS (Q-TOF, ESI) calcd for C₁₈H₁₇N₂O₃S⁺ [M + H]⁺ 341.0954, found 341.0960.

5'-Phenyl-3', 4'-dihydrospiro[indoline-3, 2'-pyrrol]-2-one (3ga): yellow solid; 61.8 mg; 79% yield; mp 217–218 ℃; ¹H NMR (400 MHz, CDCl₃) δ 9.12 (s, 1H), 7.94 (d, J = 7.1 Hz, 2H), 7.49–7.40 (m, 3H), 7.19 (t, J = 7.6 Hz, 1H), 7.11 (d, J = 7.3 Hz, 1H), 7.00 (t, J = 7.5 Hz, 1H), 6.91 (d, J = 7.7 Hz, 1H), 3.49 (ddd, J = 16.6, 9.4, 7.0 Hz, 1H), 3.42–3.34 (m, 1H), 2.65 (ddd, J = 14.5, 9.6, 5.3 Hz, 1H), 2.30 (ddd, J = 13.2, 9.6, 7.0 Hz, 1H); ¹³C NMR (100 MHz, CDCl₃) δ 180.0, 177.6, 141.0, 133.8, 132.8, 131.3, 129.3, 128.6, 128.4, 123.9, 123.0, 110.4, 82.1, 36.8, 33.0; HRMS (Q-TOF, ESI) calcd for C₁₇H₁₅N₂O⁺ [M + H]⁺ 263.1179, found 263.1180.

1-Benzoyl-6-chloro-5'-phenyl-3', 4'-dihydrospiro[indoline-3, 2'-pyrrol]-2-one (3ha): yellow solid; 99.6 mg; 83% yield; mp 119–120 ℃; ¹H NMR (400 MHz, CDCl₃) δ 8.03 (d, J = 1.7 Hz, 1H), 7.92–7.90 (m, 2H), 7.78–7.76 (m, 2H), 7.58 (t, J = 7.5 Hz, 1H), 7.52–7.42 (m, 5H), 7.25–7.17 (m, 2H), 3.45–3.38 (m, 2H), 2.68 (ddd, J = 13.6, 8.5, 5.3 Hz, 1H), 2.36–2.25 (m, 1H); ¹³C NMR (100 MHz, CDCl₃) δ 178.3, 176.6, 169.2, 141.0, 135.4, 133.8, 133.4, 133.1, 131.7, 130.2, 129.5, 128.7, 128.5, 128.3, 125.7, 124.9, 116.1, 81.8, 37.0, 33.7; HRMS (Q-TOF, ESI) calcd for C₂₄H₁₈ClN₂O₂⁺ [M + H]⁺ 401.1051, found 401.1057.

1-Benzoyl-7-chloro-5'-phenyl-3', 4'-dihydrospiro[indoline-3, 2'-pyrrol]-2-one (3ia): yellow solid; 90.0 mg; 75% yield; mp 191–192 ℃; ¹H NMR (400 MHz, CDCl₃) δ 8.08–8.06 (m, 2H), 7.92–7.90 (m, 2H), 7.64 (t, J = 7.4 Hz, 1H), 7.53–7.36 (m, 6H), 7.20–7.14 (m, 2H), 3.48–3.34 (m, 2H), 2.71 (ddd, J = 13.6, 8.6, 5.1 Hz, 1H), 2.40–2.32 (m, 1H); ¹³C NMR (100 MHz, CDCl₃) δ 178.5, 177.1, 168.6, 138.3, 135.1, 134.5, 133.4, 133.2, 131.6, 131.1, 128.7, 128.6, 128.4, 126.2, 122.3, 119.8, 82.9, 36.9, 34.2; HRMS (Q-TOF, ESI) calcd for C₂₄H₁₈ClN₂O₂⁺ [M + H]⁺ 401.1051, found 401.1056.

1-Benzoyl-5-chloro-5'-phenyl-3', 4'-dihydrospiro[indoline-3, 2'-pyrrol]-2-one (3ja): yellow solid; 102.8 mg; 85% yield; mp 143–144 ℃; ¹H NMR (400 MHz, CDCl₃) δ 7.94–7.90 (m, 3H), 7.77–7.75 (m, 2H), 7.57 (t, J = 7.3 Hz, 1H), 7.52–7.39 (m, 6H), 7.23–7.25 (m, 1H), 3.44–3.40 (m, 2H), 2.69 (ddd, J = 13.5, 8.1, 5.7 Hz, 1H), 2.37–2.29 (m, 1H); ¹³C NMR (100 MHz, CDCl₃) δ 178.6, 176.3, 169.2, 138.7, 133.9, 133.5, 133.3, 133.0, 131.7, 131.1, 129.7, 129.5, 128.7, 128.5, 128.3, 124.3, 116.9, 81.9, 37.0, 33.8; HRMS (Q-TOF, ESI) calcd for C₂₄H₁₈ClN₂O₂⁺ [M + H]⁺ 401.1051, found 401.1060.

1-Benzoyl-5-fluoro-5'-phenyl-3', 4'-dihydrospiro[indoline-3, 2'-pyrrol]-2-one (3ka): yellow solid; 94.0 mg; 82% yield; mp 193–194 ℃; ¹H NMR (400 MHz, CDCl₃) δ 7.97 (dd, J = 8.9, 4.5 Hz, 1H), 7.92–7.90 (m, 2H), 7.77–7.74 (m, 2H), 7.57 (t, J = 7.5 Hz, 1H), 7.52–7.42 (m, 5H), 7.13 (td, J = 9.0, 2.7 Hz, 1H), 6.98 (dd, J = 7.5, 2.7 Hz, 1H), 3.44–3.39 (m, 2H), 2.69 (ddd, J = 13.6, 8.6, 5.1 Hz, 1H), 2.36–2.28 (m, 1H); ¹³C NMR (100 MHz, CDCl₃) δ 178.6, 176.6, 169.3, 160.7 (d, J = 244.9 Hz), 136.1 (d, J = 2.5 Hz), 134.1, 133.6 (d, J = 7.9 Hz), 133.3, 132.9, 131.7, 129.4, 128.7, 128.5, 128.3, 117.1 (d, J = 7.9 Hz), 116.3 (d, J = 23.0 Hz), 111.4 (d, J = 24.3 Hz), 82.0, 37.0, 33.9; ¹⁹F NMR (376 MHz, CDCl₃) δ –115.99; HRMS (Q-TOF, ESI) calcd for C₂₄H₁₈FN₂O₂⁺ [M + H]⁺ 385.1347, found 385.1331.

1-Benzoyl-5-bromo-5'-phenyl-3', 4'-dihydrospiro[indoline-3, 2'-pyrrol]-2-one (3la): yellow solid; 119.0 mg; 89% yield; mp 141–142 ℃; ¹H NMR (400 MHz, CDCl₃) δ 7.94–7.85 (m, 3H), 7.76–7.74 (m, 2H), 7.60–7.37 (m, 7H), 7.37 (d, J = 2.0 Hz, 1H), 3.48–3.35 (m, 2H), 2.68 (ddd, J = 13.7, 8.3, 5.6 Hz, 1H), 2.37–2.30 (m, 1H); ¹³C NMR (100 MHz, CDCl₃) δ 178.6, 176.2, 169.2, 139.2, 133.9, 133.8, 133.3, 133.1, 132.6, 131.7, 129.5, 128.7, 128.5, 128.3, 127.1, 118.6, 117.2, 81.8, 37.0, 33.8; HRMS (Q-TOF, ESI) calcd for C₂₄H₁₈BrN₂O₂⁺ [M + H]⁺ 445.0546, found 445.0544.

1-Benzoyl-5-methyl-5'-phenyl-3', 4'-dihydrospiro[indoline-3, 2'-pyrrol]-2-one (3ma): yellow solid; 100.0 mg; 88% yield; mp 171–172 ℃; ¹H NMR (400 MHz, CDCl₃) δ 7.93–7.91 (m, 2H), 7.86 (d, J = 8.3 Hz, 1H), 7.77–7.75 (m, 2H), 7.56 (t, J = 7.5 Hz, 1H), 7.51–7.41 (m, 53H), 7.23 (dd, J = 8.3, 1.0 Hz, 1H), 7.06 (s, 1H), 3.43–3.39 (m, 2H), 2.67 (ddd, J = 13.7, 8.1, 5.8 Hz, 1H), 2.38–2.30 (m, 4H); ¹³C NMR (100 MHz, CDCl₃) δ 177.9, 177.1, 169.4, 137.8, 135.5, 134.4, 133.6, 132.7, 131.7, 131.5, 130.2, 129.4, 128.6, 128.5, 128.3, 124.4, 115.4, 82.2, 37.0, 33.9, 21.3; HRMS (Q-TOF, ESI) calcd for C₂₅H₂₁N₂O₂⁺ [M + H]⁺ 381.1598, found 381.1582.

1-Benzoyl-5-methoxy-5'-phenyl-3', 4'-dihydrospiro[indoline-3, 2'-pyrrol]-2-one (3na): yellow solid; 100.0 mg; 84% yield; mp 149–150 ℃; ¹H NMR (400 MHz, CDCl₃) δ 7.95–7.90 (m, 3H), 7.75–7.73 (m, 2H), 7.57–7.41 (m, 6H), 6.95 (dd, J = 8.9, 2.7 Hz, 1H), 6.79 (d, J = 2.7 Hz, 1H), 3.81 (s, 3H), 3.42–3.38 (m, 2H), 2.68 (ddd, J = 13.5, 8.4, 5.2 Hz, 1H), 2.37–2.29 (m, 1H); ¹³C NMR (100 MHz, CDCl₃) δ 178.2, 176.9, 169.3, 157.9, 134.5, 133.5, 133.0, 132.6, 131.6, 129.3, 128.6, 128.5, 128.2, 116.8, 114.7, 109.9, 82.3, 55.9, 37.0, 34.0; HRMS (Q-TOF, ESI) calcd for C₂₅H₂₁N₂O₃⁺ [M + H]⁺ 397.1547, found 397.1539.

5'-(2-Chlorophenyl)-1-tosyl-3', 4'-dihydrospiro[indoline-3, 2'-pyrrol]-2-one (3ab): yellow solid; 65.0 mg; 48% yield; mp 134–135 ℃; ¹H NMR (400 MHz, CDCl₃) δ 7.91 (d, J = 8.3 Hz, 2H), 7.86 (d, J = 8.2 Hz, 1H), 7.52 (dd, J = 7.7, 1.6 Hz, 1H), 7.33–7.11 (m, 8H), 3.45–3.29 (m, 2H), 2.53 (ddd, J = 13.5, 8.8, 4.8 Hz, 1H), 2.32 (s, 3H), 2.21–2.13 (m, 1H); ¹³C NMR (100 MHz, CDCl₃) δ 179.8, 175.0, 145.8, 139.0, 135.2, 133.9, 132.6, 131.35, 130.8, 130.4, 129.99, 129.96, 128.0, 127.0, 125.5, 124.2, 113.8, 81.1, 39.9, 35.1, 21.8; HRMS (Q-TOF, ESI) calcd for C₂₄H₂₀ClN₂O₃S⁺ [M + H]⁺ 451.0878, found 451.0881.

5'-(3-Chlorophenyl)-1-tosyl-3', 4'-dihydrospiro[indoline-3, 2'-pyrrol]-2-one (3ac): yellow solid; 95.4 mg; 71% yield; mp 148–149 ℃; ¹H NMR (400 MHz, CDCl₃) δ 8.00–7.94 (m, 3H), 7.84–7.83 (m, 1H), 7.67 (d, J = 7.7 Hz, 1H), 7.44–7.31 (m, 5H), 7.19 (td, J = 7.5, 0.8 Hz, 1H), 7.12 (dd, J = 7.4, 1.0 Hz, 1H), 3.40–3.30 (m, 2H), 2.62 (ddd, J = 13.4, 8.8, 4.6 Hz, 1H), 2.42 (s, 3H), 2.26–2.18 (m, 1H); ¹³C NMR (100 MHz, CDCl₃) δ 177.5, 175.2, 145.9, 139.1, 135.2, 135.1, 134.8, 131.5, 130.9, 130.1, 130.0, 129.9, 128.4, 128.1, 126.6, 125.6, 124.1, 113.9, 81.7, 36.6, 34.5, 21.8; HRMS (Q-TOF, ESI) calcd for C₂₄H₂₀ClN₂O₃S⁺ [M + H]⁺ 451.0878, found 451.0868.

5'-(4-Chlorophenyl)-1-tosyl-3', 4'-dihydrospiro[indoline-3, 2'-pyrrol]-2-one (3ad): yellow solid; 97.0 mg; 72% yield; mp 192–193 ℃; ¹H NMR (400 MHz, CDCl₃) δ 8.00–7.94 (m, 3H), 7.77–7.74 (m, 2H), 7.41–7.30 (m, 5H), 7.20–7.11 (m, 2H), 3.40–3.29 (m, 2H), 2.60 (ddd, J = 13.4, 8.8, 4.6 Hz, 1H), 2.41 (s, 3H), 2.25–2.17 (m, 1H); ¹³C NMR (100 MHz, CDCl₃) δ 177.6, 175.3, 145.9, 139.0, 137.7, 135.2, 131.9, 131.0, 130.02, 129.97, 129.7, 128.9, 128.1, 125.5, 124.1, 113.9, 81.7, 36.6, 34.6, 21.8; HRMS (Q-TOF, ESI) calcd for C₂₄H₂₀ClN₂O₃S⁺ [M + H]⁺ 451.0878, found 451.0863.

5'-(4-Fluorophenyl)-1-tosyl-3', 4'-dihydrospiro[indoline-3, 2'-pyrrol]-2-one (3ae): yellow solid; 101.2 mg; 78% yield; mp 191–192 ℃; ¹H NMR (400 MHz, CDCl₃) δ 7.99 (d, J = 8.3 Hz, 2H), 7.95 (d, J = 8.3 Hz, 1H), 7.83 (dd, J = 8.6, 5.5 Hz, 2H), 7.38 (t, J = 7.2 Hz, 1H), 7.31 (d, J = 8.2 Hz, 2H), 7.18 (t, J = 7.5 Hz, 1H), 7.13 (d, J = 7.4 Hz, 1H), 7.06 (t, J = 8.6 Hz, 2H), 3.38–3.27 (m, 2H), 2.60 (ddd, J = 13.4, 8.6, 4.8 Hz, 1H), 2.41 (s, 3H), 2.24–2.17 (m, 1H); ¹³C NMR (100 MHz, CDCl₃) δ 177.4, 175.4, 164.8 (d, J = 252.3 Hz), 145.8, 139.0, 135.2, 131.1, 130.6 (d, J = 8.8 Hz), 130.0, 129.7 (d, J = 3.1 Hz), 128.1, 125.5, 124.1, 115.7 (d, J = 21.8 Hz), 113.8, 81.6, 36.6, 34.7, 21.8; ¹⁹F NMR (376 MHz, CDCl₃) δ -107.98 HRMS (Q-TOF, ESI) calcd for C₂₄H₂₀FN₂O₃S⁺ [M + H]⁺ 435.1173, found 435.1168.

5'-(4-Bromophenyl)-1-tosyl-3', 4'-dihydrospiro[indoline-3, 2'-pyrrol]-2-one (3af): yellow solid; 113.2 mg; 76% yield; mp 196–197 ℃; ¹H NMR (400 MHz, CDCl₃) δ 8.00–7.94 (m, 3H), 7.68 (d, J = 8.6 Hz, 2H), 7.51 (d, J = 8.6 Hz, 2H), 7.38 (td, J = 8.0, 1.5 Hz, 1H), 7.31 (d, J = 8.1 Hz, 2H), 7.18 (t, J = 7.1 Hz, 1H), 7.12 (dd, J = 7.5, 1.1 Hz, 1H), 3.39–3.29 (m, 2H), 2.60 (ddd, J = 13.4, 8.7, 4.7 Hz, 1H), 2.41 (s, 3H), 2.25–2.17 (m, 1H); ¹³C NMR (100 MHz, CDCl₃) δ 177.6, 175.2, 145.8, 139.0, 135.2, 132.3, 131.8, 131.0, 130.00, 129.95, 129.9, 128.1, 126.2, 125.5, 124.1, 113.9, 81.7, 36.5, 34.6, 21.8; HRMS (Q-TOF, ESI) calcd for C₂₄H₂₀BrN₂O₃S⁺ [M + H]⁺ 495.0373, found 495.0368.

5'-(p-Tolyl)-1-tosyl-3', 4'-dihydrospiro[indoline-3, 2'-pyrrol]-2-one (3ag): yellow solid; 104.2 mg; 81% yield; mp 146–147 ℃; ¹H NMR (400 MHz, CDCl₃) δ 8.00 (d, J = 8.3 Hz, 2H), 7.94 (d, J = 8.2 Hz, 1H), 7.72 (d, J = 8.1 Hz, 2H), 7.39–7.35 (m, 1H), 7.31 (d, J = 8.1 Hz, 2H), 7.20–7.11 (m, 4H), 3.41–3.33 (m, 2H), 2.63–2.56 (m, 1H), 2.41 (s, 3H), 2.38 (s, 3H), 2.23–2.15 (m, 1H); ¹³C NMR (100 MHz, CDCl₃) δ 178.6, 175.6, 145.8, 142.1, 139.0, 135.3, 131.4, 130.7, 130.0, 129.9, 129.3, 128.5, 128.1, 125.5, 124.2, 113.8, 81.5, 36.5, 34.8, 21.8, 21.7; HRMS (Q-TOF, ESI) calcd for C₂₅H₂₃N₂O₃S⁺ [M + H]⁺ 431.1424, found 431.1420.

5'-(4-(tert-Butyl)phenyl)-1-tosyl-3', 4'-dihydrospiro[indoline-3, 2'-pyrrol]-2-one (3ah): yellow solid; 110.0 mg; 78% yield; mp 182–183 ℃; ¹H NMR (400 MHz, CDCl₃) δ 8.00 (d, J = 8.3 Hz, 2H), 7.95 (d, J = 8.2 Hz, 1H), 7.78 (d, J = 8.4 Hz, 2H), 7.43–7.30 (m, 5H), 7.19–7.11 (m, 2H), 3.40–3.32 (m, 2H), 2.60 (ddd, J = 13.4, 8.7, 4.7 Hz, 1H), 2.41 (s, 3H), 2.22–2.15 (m, 1H), 1.33 (s, 9H); ¹³C NMR (100 MHz, CDCl₃) δ 178.5, 175.5, 155.2, 145.8, 139.0, 135.3, 131.4, 130.7, 129.9, 129.8, 128.3, 128.1, 125.5, 125.5, 124.1, 113.8, 81.5, 36.5, 35.0, 34.8, 31.2, 21.8; HRMS (Q-TOF, ESI) calcd for C₂₈H₂₉N₂O₃S⁺ [M + H]⁺ 473.1893, found 473.1872.

1-Methyl-3-methyleneindolin-2-one (4a): known product [37], ¹H NMR (400 MHz, CDCl₃) δ 7.47 (d, J = 7.4 Hz, 1H), 7.30 (dd, J = 7.8, 1.0 Hz, 1H), 7.03 (td, J = 7.6, 0.9 Hz, 1H), 6.81 (d, J = 7.8 Hz, 1H), 6.40 (s, 1H), 6.10 (s, 1H), 3.24 (s, 3H); HRMS (Q-TOF, ESI) calcd for C₁₀H₁₀NO⁺ [M + H]⁺ 160.0757, found 160.0790.

Our investigation started with the optimization of the reaction conditions, using the easily prepared 3-diazo-1-methylindolin-2-one (1a) and (1-azidovinyl)benzene (2a) reactants as model substrates. The initial experiments were performed by heating 1a and 2a (3 equiv.) at 60 ℃ in toluene for 10 h, in the presence of AgSbF₆ (10 mol%) or PPh₃AuCl/AgSbF₆ (10 mol%, Au/Ag = 1:1). However, the desired product 3aa was not detected under these conditions (Table 1, entries 1 and 2). On the other hand, the dirhodium carboxylates showed high efficiency for this same transformation, giving the desired product 3aa in moderate yields (Table 1, entries 3–5). The structure of 3aa was unambiguously confirmed by ¹H and ¹³C NMR, along with HRMS and single-crystal X-ray diffraction measurements. This encouraging result prompted us to examine the effect of various reaction parameters, such as solvent and temperature, and the results are summarized in Table 1. Screening of different solvents showed that the best results were achieved with DCE (entries 6–10). Considering the decomposition of 2a, the yield of 3aa increased to 81% when 7 equiv. of 2a was employed in the reaction (entries 11–13). We also investigated different temperatures, with no improvement in the reaction outcome (entries 14 and 15). Moreover, decreasing the amount of catalyst resulted in a lower yield (entry 16). Hence, the optimized reaction conditions were determined to be 1a (0.1 mmol), 2a (0.7 mmol), Rh₂(TFA)₄ (2.5 mol%), and DCE (1 mL), heated at 60 ℃ under argon atmosphere for 10 h.

Having determined the optimal reaction conditions, we explored the generality of the present approach. The results are summarized in Scheme 3.

The N-protecting groups of substrate 1 were first investigated. To our delight, various protecting groups including alkyl, benzyl, phenyl, benzoyl, and sulfonyl groups provided good results (3aa–3fa). In particular, the yields of 3da and 3ea reached up to 90%, while the methylsulfonyl group led to a decrease in the product yield (3fa, 74%). Notably, unprotected 3-diazooxindole (1g) reacted with 2a as well, generating the target product 3ga in 80% yield. Next, the substituents on the phenyl ring of 1 were examined. Substituents with different electronic effects on the phenyl ring of the 1-benzoyl-3-diazooxindole (1d) compound were well tolerated (3ha–3na). With a halogen (Cl) group at the C5-, C6- or C7-position of the phenyl ring, the annulation resulted in the corresponding spirocyclic products in moderate to good yields (3ha–3ja). The steric effect of 1-benzoyl-7-chloro-3-diazooxindole (1i) caused a small decrease in the yield (75% vs. 85%). The electronic effect of substituents at the C5-position had little influence on the yields (3ja–3na, 82%–89%). A similar phenomenon was observed when various substituents were introduced in the phenyl group of the vinyl azide 2, yielding the products in moderate to good yields (3ab–3ah, 48%–81%).

Control experiments were conducted to investigate the reaction mechanism (Scheme 4). After stirring a mixture of 1a, 2a, and Rh₂(TFA)₄ in DCE at 60 ℃ for 1 h, an unexpected product (4a) was isolated in 52% yield, in addition to the desired product 3aa (34% yield). Since a 79% yield of product 3aa was obtained after prolonging the reaction time to 10 h (Table 1, entry 12), it is reasonable to conclude that compound 4a was the key intermediate of the process. In addition, when the reaction was carried out at room temperature (rt) for 10 h, compound 4a was observed as well. The reaction of 4a with 2a was also conducted under standard reaction conditions, affording the desired product 3aa in 67% yield (Scheme 4).

On the basis of these results [34], a plausible mechanism was proposed, using the reaction of the 3-diazooxindole 1a and vinyl azide 2a as an example (Scheme 5). The Rh(Ⅱ)-catalyzed denitrogenation of 1a generates the electrophilic rhodium carbenoid A. Next, the nucleophilic addition of 2a to the carbenoid A gives the intermediate B, followed by the formation of the key intermediate 4a with loss of N₂ and phenylacetonitrile. It should be noted that although the intermediate 4a can be isolated, it is unstable. Finally, compound 4a reacts with another molecule of 2a to yield the product 3aa through a [2+2] cycloaddition/ring expansion sequence.

Potentially bioactive spiropyrrolidine oxindoles were synthesized by the Rh(Ⅱ)-catalyzed [1+1+3] annulation of 3-diazooxindoles and vinyl azides through an olefination/cyclization sequence. This transformation is highly efficient and tolerates various substituents. Owing to its mild conditions, broad scope, and high efficiency, this approach is likely to find application in the synthesis of a wide range of spirocyclic compounds.