Acetylenes formation from lactones

Suitable catalysts for ring closure reactions are cobalt carbonyls [123, 280, 673, 674], rhodium carbonyls [280, 678], iron carbonyl [123] and certain palladium compounds [679]. Nickel carbonyls, the active catalysts in the Reppe syntheses, are inactive in most cases [123, 673]. A few examples in which nickel is active are the formation of phenols from allyl halides, acetylene and carbon monoxide, which is only a side reaction, and the mechanistically unclear formation of lactones from allyl carbinol and bu-tyne-l-ol-4 [438]. 

An insight into the mechanism of metal-catalysed formation of lactones from acetylenes, carbon monoxide, and alkyl, allyl, or aryl halides is provided by the reactions of [MRCCOaC -CsHs)] (M = Mo or W R=Me, CHjPh, or COCFs) which indicate that migration of the R group on to co-ordinated CO is followed by acetylene insertion and to give (1) (Scheme 1). The second CO insertion leading to the... 

Of more specialized interest is the reaction of alkynes with Co2(CO)s in polar solvents under conditions of elevated temperature and CO pressure. The major products are the (E) and (Z) isomers of so-called bifurandiones, the products of formal (but not actual) carbene dimerization. An intermediate, a complex of this lactone-derived carbene bridging a Co2(CO>7 moiety, may be isolated from reactions of alkyl-, aryl- or dialkyl-acetylenes with Co2(CO)8. Its formation is completely regioselective even for ethyl vj. methyl, placing the larger group a to the lactone carbonyl. - In the subsequent formation of the bifurandione itself regioselectivity in alkyne incorporation into the second ring is incomplete and in the opposite direction, an observation which remains unexplained (Scheme 11). ... 

In a recent paper Cassar et, aL [801] reported the formation of unsaturated s-lactones of the type below from acid halides, Ni(CO)4 and acetylene at low concentrations of carbon monoxide. 

A more plausible sequence has been suggested (Bohlmann, Bornowski and Arndt, I962) in which lactone formation proceeds by the more usual dehydration route and does not involve an acetylenic bond. The precursor would arise ultimately from the same poly-)S-diketone as frutescin (LXIII) itself. 

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