Enantioselective Synthesis and X‐ray Structure of (+)((4a S ,5 S ,8a S )‐5,8a‐Dimethyl‐7‐methyleneoctahydro‐2 H ‐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 .