Enantioselective synthesis and X-ray structure of (+)((4aS,5S,8aS)-5,8a-Dimethyl-7-methyleneoctahydro-2H-spiro[naphthalene-1,2′-[1,3]dioxolan]-5-yl)methyl-4-iodobenzoate

The d and l amino acid mediated enantioselective intramolecular aldol reaction of 4-((1-methyl-2,6-dioxo-cyclohexyl)methyl)-pent-4-enal 1 leading, after dehydration, to (-)-(R) and (+)-(S) 4a-methyl-3-methylene-5-oxo-2,3,4,4a,5,6,7,8-octahydro-naphthalene-1-carbaldehyde 2 was explored. It was found that (-)-(R) carbaldehyde 2 is enantioselectively formed in the presence of l-amino acids while (+)-(S) carbaldehyde 2 is enantioselectively formed in the presence of d-amino acids. (-)-(R) Carbaldehyde 2 was then transformed into (+)-22. The absolute configuration and relative stereochemistry of the latter was established by single-crystal X-ray diffraction analysis of p-iodobenzoate (+)-23.