ChemInform Abstract: Alkynylhalocarbenes: Generation from 1,1-Dihaloalk-2-ynes by Base Solvolysis and Reaction with Alkenes

A series of 1,1-dihaloalk-2-ynes 1–3 has been prepared by halogenation of the formylacetylenes 8 with PCl5 or an equimolar mixture of PCl5 and Br2. A simple, general means of access to the alkynylhalocarbenes 5 has been developed via base-initiated α-elimination of 1,1-dihaloalk-2-ynes (1–3). The carbenes 5a–i have been trapped by alkenes, to form 1-alkynyl-1-halocyclopropanes (11) in up to 90% yield. Under the same conditions compound 1g was converted into the buta-diene 12. Experimental evidence for the electrophilicity and the singlet nature of carbenes 5 has been obtained.