Alkynylhalocarbenes

(Alk-1-ynyl)chlorocarbenes (3), generated from 1,1-dihaloalk-2-ynes and 3-substituted 3-bromo-1,1,1-trichloropropanes under the action of ButOK in THF at 20°C, react with excess alkali metal alkoxide4 to give 3-substituted 2-(alk-1-ynyl)oxiranes (6) in 26–78% yields, most likely as a result of insertion of carbene3 into the α-C−H bond of alkoxides4 and subsequent cyclization of the resulting 1-substituted 2-chloro-2-(alk-1-ynyl)etoxides. The yields of oxiranes6 depend on the nature of the alkali metal used to prepare alkoxides4 and on the method employed for the preparation of the latter.