Synthesis of Cross-Conjugated Geminal Enediynes via Palladium Catalyzed Cross-Coupling Reaction of Ketene Butyltelluroacetals

Abstract

The palladium-catalyzed cross coupling reaction of ketene butyltelluroacetals with terminal alkynes at room temperature affords cross-conjugated geminal enediynes in high yield under mild conditions.

Key words

cross-coupling - enynes - palladium - tellurium - ketene butyltellurocetals

References and Notes

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12

Typical procedure for 8a: To a two-necked 25 mL round-bottomed flask under argon atmosphere containing PdCl₂ (0.035 g, 20 mol%) and dry methanol (5 mL) was added the ketene butyltelluroacetal 6a (0.470g, 1 mmol). After stirring the mixture for 15 minutes at room temperature, 1-heptyne (0.192 g, 2 mmol) and Et₃N (0.8 mL) were added. The reaction was stirred at room temperature for 4 h. After this time, the solids were filtered under vacuum, to the filtrate was added brine. The organics were extracted with dichloromethane (3 × 25 mL), dried over MgSO₄ and concentrated under vacuum. The residue was purified by flash silica gel chromatography eluting with hexane; Yield 0.227 g (75%). Selected spectral and analytical data for 8a: ¹H NMR (CDCl₃, 200 MHz) δ(ppm): 7.86-7.82(m, 2 H), 7.33-7.30(m, 3 H), 6.89(s, 1 H), 2.42(t, 7.0 Hz, 2 H), 2.37(t, 7.0 Hz, 2 H), 1.75-1.20(m, 12 H), 0.96(t, 7.0 Hz, 3 H), 0.93(t, 7.0 Hz, 3 H); ¹³C NMR (CDCl₃, 50 MHz) δ(ppm): 140.93, 135.99, 128.52, 128.38, 128.10, 104.08, 96.99, 88.92, 80.98, 78.61, 31.28, 31.14, 28.34, 28.01, 22.47, 22.22, 19.96, 19.80, 13.95, 13.80; IR (neat, cm^-1): 3060, 2200, 2190, 1660, 786; LRMS (rel. int.) m/z 292(100), 178(80), 152(40), 91(50), 77(60).