The synthesis and stereochemistry of allenee, acetylenes and related compounds

Abstract

(±)-Marasin, claimed to be the product from the reduction of non-2-en-4,6,8-triyn-1-ol with lithium aluminium hydride, has been shown to be a minor product only, the major product being the allenene. Reduction with dialkoxylithium aluminium hydride gave improved yields of allenynes together with allenenes whereas the lithium aluminium hydride-butane-2,3-diol complex gave allenynes only. Reduction with the asymmetric complexes of lithium aluminium hydride with menthol, and 3-0-benzyl-1,2-0- cyclohexylidene-x-D-glucofuranose gave the optically active allenynes, A consideration of the stereochemistry of these reductions enabled the configuration of the product to be predicted. The absolute configurations of four allenynes, Including the naturally occurring marasin and its next higher homologue (9-methyl marasin) were determined. The lithium aluminium hydride-active amyl alcohol (2-methyl- butan-1-ol) complex was found to be unsuitable for producing optically active allenynes. The kinetically controlled reduction of 4-ohloro-2-yn-1-ols and the corresponding acetates with an asymmetric complex has been investigated. The absolute configuration of (+)-hexa-3,4-dienol has been determined by application of the Claisen rearrangement to optically active (-)-chloroethyl but-1-yn-3-yl ether. Trace impurities in 3-0-henzyl-1,2-0~cyclohexylidene- (X-D-glucofuranose have been isolated, and identified and the analytically pure compound prepared for the first time. 3,3,5-Trimethylcyelohexanone has been reduced with cyclic complexes of lithium aluminium hydride. The axial/equatorial ratio of the cyclohexanols obtained from these and other reductions has been Interpreted by postulating the participation of the flexible form of the ketone in the reduction. Bromopropargyl aldehyde has been synthesised for the first time and attempts to use this compound as an intermediate are described.