ALLENYL ENOLATES - A NEW CLASS OF CHIRAL AMBIDENT NUCLEOPHILES .2. REACTION WITH IODINE AND OXIDIZING-AGENTS

The reaction of allenyl enolates, obtained by 1,6-addition of lithium dimethylcuprate to 2-en-4-ynoates 1a/b, with iodine is studied. Whereas the n-butyl-substituted enyne 1a gives a mixture of vinyl iodide 2a (48%) and methylated allene 3a (7%), the tert-butyl-substituted enyne 1b yields allene 3b (70%) exclusively. The products 2a and 3a are also obtained if Br2, O2, or CuCl2 are used to trap the allenyl enolate derived from 1a and Me2CuLi . LiI. These findings are discussed with the assumption that iodo-allene 5 and the iodo-containing Gilman cuprate [Me2Cu(I)Li2]2 are acting as intermediates.