The reaction of trialkylboranes with wtosyloxy-l-lithio-1-alkynes can induce transfer of a n alkyl group froiii the boron atom to the alkynyl carbon atom with concomitant formation of four-through six-menibered carbocycles via intramolecular displacement of the w tosyloxy group. The stereoselectivity of the reaction, however, is low (anti/syn=1.61.7). The corresponding reaction of w h a b -or wtosyloxy-1-alkenylborates also gives exocyclic alkvnes via 1,2-inigration-cyclization followed by dehydroboration. I n the cases of cyclopropanation, cyclopropylcarbinyl-to-hornopropargyl rearrangement rather than dehydroboration takes place. Diphenylzirconocene reacts similarly with 6- lithio-5-hexynyl tosylate to give pheizybnethylenecyclopentaize in 45% vield. On the other hand, attempts to induce a similar iiiigration with phenyl derivatives of X Cr, and Mn have led to < 5-10% yields of the same cyclization product.
1 -1ithio-w-tosyloxy-1 -alkynes or 1 -1ithio-w-halo-1alkynes at -78°C in THE and the reaction mixtures Me3AI c " ; cat. cp2zrc12 80% LiC 5 CSiMe, HMPA -FSiM w 77?4 1. 9-BBN