Novel Syntheses of α,β-Unsaturated Esters, α,β-Unsaturated γ-Lactones, and 2-Alkoxypyrroles via 1,2,4-Triazole-Stabilized Allenic Anions

The dianion 12 (⇌ 13) of 1-(1,2,4-triazol-1-yl)phenylpropargyl ethyl ether 11 (readily prepared from phenylpropargylaldehyde diethyl acetal 8 and 1,2,4-triazole) reacts with alkyl halides, aldehydes, ketones, and α,β-unsaturated ketones to give exclusively γ-substituted allenic products of type 10. These adducts underwent mild in situ hydrolysis enabling convenient syntheses of α,β-unsaturated esters 9a − c and α,β-unsaturated γ-lactones 16, 18, 20, and 22. Reactions of dianion 13 with imines generated the 1,3,4-trisubstituted 2-alkoxypyrroles 27, 30, and 31 in high yields. The alkyl-substituted analog 34 underwent similar reactions to give predominantly the γ-products 39, 40, and 42 along with a small proportion of α-analogs.