All four stereoisomers of 2,6-dimethyloctan-1-ol, the nearest precursors of the title formates, were synthesized in five to eight stages, with configurational purity ranging from 41 to 96 %, employing a stereodivergent scheme based on the partial hydrolysis of two pseudoracemic substrates, (2RS,6R)-2,6-dimethyloct-1-yl formate and (2RS,6S)-2,6-dimethyloct-1-yl acetate, in the presence of porcine pancreatic lipase (PPL). Configurations and diastereomeric compositions of the alcohols thus obtained were determined by correlating the latter with (S,S)-4,8-dimethyldecanal, prepared on the basis of enantioselective biohydrogenation of (R)-2,6-dimethylocta-2,7-dienal with bakers' yeast, and by comparing the [alpha](D) values of the alcohols with their NMR data and/or with those of their (S)-MTPA derivatives. The attractant potency of stereoisomeric 2,6-dimethyloct-1-yl formates towards Tribolium confusum was found to vary depending on their diastereomeric composition. The configuration at C(6) exerts some influence on the stereoselectivity of the PPL-catalyzed hydrolysis of pseudoracemic 2,6-dimethyloct-1-yl formates.
Tandem addition–cyclization mediated by sulfanyl radicals: a versatile strategy for iridoids synthesis
作者:Elena M. Sánchez、Jesús F. Arteaga、Victor Domingo、José F. Quílez del Moral、M. Mar Herrador、Alejandro F. Barrero
DOI:10.1016/j.tet.2008.03.058
日期:2008.5
Sulfanyl radicals trigger a tandemaddition–cyclization protocol in linalool or citronelene derivatives for the efficient construction of the iridane monoterpene skeleton. Best results in yields and diastereoselectivity were obtained when phenylethylsulfanyl was used as radical initiator. We have proved the utility of this protocol with the enantiospecific synthesis of natural iridane dehydroiridomyrmecin