Diastereoreactivity of a Chiral Oxathiane Derived from 5-Hydroxy-1-tetralone

The diastereoreactivity at the CH2 bridge of a cis‐oxathiane derived from 5‐hydroxy‐1‐tetralone (unprotected and protected at the OH) was studied, and it appeared that all reactions at C‐2 provided equatorial substitution. It was also found that: i) reductions of the equatorial benzoyl derivative with selectrides provided high diastereoselectivities at C‐2′ while LAH did not. Methyl Grignard addition was less selective and the selectivity of the propanoyl analogue was smaller; ii) condensation of aldehydes and/or ketones with the lithio derivative provided high equatorial diastereoselectivities at C‐2 but low or nil diastereoselectivities at C‐2′; iii) lithiation at C‐2 was possible only with the oxathiane unsubstituted at C‐2 (CH2) and not possible with derivatives substituted at C‐2 (CHR), perhaps due to the conformational rigidity of this oxathiane in the lithiation transition state and to the equatorial demand of all substituents at C‐2, including lithium. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)