Alkylative carbocyclization of omega-iodoalkynyl tosylates with alkynyllithium compounds through a carbenoid-chain process leading to (1-iodoprop-2-ynylidene)tetrahydrofurans and -cyclopropanes.

Alkylative carbocyclization reactions of omega-iodoalkynyl tosylates with alkynyllithium compounds to give products with incorporated iodine atoms are described. Slow addition of 2-(3-iodoprop-2-ynyloxy)ethyl tosylates to 1-alkynyllithium compounds in tetrahydrofuran at 40 degrees C followed by additional stirring at this temperature gives (Z)-3-(1-iodoprop-2-ynylidene)tetrahydrofurans stereoselectively in good to moderate yields. Under similar conditions at 0 degrees C, 4-iodobut-1-ynyl tosylates react with 1-alkynyllithium compounds to give (1-iodoprop-2-ynylidene)cyclopropanes. The carbocyclization reactions are proposed to proceed through a new carbenoid-chain process involving the exo cyclization of a lithium acetylide intermediate and the vinylic substitution of the resulting TsO,Li-cycloalkylidenecarbenoids (Ts=tosyl) by 1-alkynyllithium compounds.