New Approaches to the Synthesis of Vitamin D Metabolites. 2. The Effect of Some Substituents on Stereochemistry in the Intramolecular Cycloadditions of Nonatrienes

Article abstract of DOI:10.1021/jo00228a040

Intramolecular Diels-Alder reactions of 8-methyl-1,3,8-nonatrienes 5 and 6 were studied to determine the effects of substituents on the stereochemistry of ring closure.Substituents at C-3 favor closure to trans-hydrindenes; likewise, a C-7 alkyl group favors closure to trans-hydrindene products.Substrates bearing a C-7 alkyl substituent afforded products in which the alkyl substituent was invariably cis to the angular methyl group (34 and 35).The ratio of trans:cis fused hydrindenes was shown to be solvent-dependent; yields were improved when closures were effected in dimethylaniline.