New 2-acyl-1,3-dioxane derivatives from (1R)-(−)-myrtenal: stereochemical effect on their relative ability as chiral auxiliaries

Four 3,10-pinanediol derivatives 1a-d, prepared in 50-72% global yields from (1R)-(−)-myrtenal 2, were treated with (RO)2CHCOR3 (R3 = CH3, Ph) to afford 2-acyl-1,3-dioxanes 3a-f. The latter were submitted to nucleophilic additions using several Grignard reagents to mainly afford carbinols generated by re diastereofacial attack (85-99% yield, ⩾88:12 dr). The lowest diastereoselectivity was observed when PhLi or hydrides were used as nucleophiles. Only an equatorial substituent at C-3 modifies the diastereoselectivity of the nucleophilic additions.