“…The first to report such reactions was Marvel (196,542), who treated abromoacetylenes with sodium amalgam or magnesium and obtained alienes and allenic acids when the resulting solutions were hydrolyzed or carbonated (Eq 13). Subsequent work on reactions of this type has Na-Hg, ether; H,0® /-" /-BuC==CCBr Ph-i-Bu \ Mg,, ether; C02, H ¡Oá £-BuCH= C= CPh-i-Bu (Eq 13) i-BuO=C=CPh-t-Bu co2h led to a general method for the synthesis of allenecarboxylic acids, which consists of the treatment of propargyl bromides with magnesium, followed by carbonation of the resulting Grignard solution (205,462,605,606,608,609) (Eq 14). Unfortunately the allenic For some time it was assumed that the organometallic intermediate in such reactions is an acetylenic Grignard reagent, but extensive study has shown that in many cases, if not in all, it contains the allenic bond system (194,245,270,376,418,463).…”