The preparation of optically active 3-aryl-1,4-dioxaspiro[4,5]decanes and their 2-oxo-derivatives; a study of the cotton effects associated with these compounds
A series of optically active mandelic acids has been prepared, including the 3,4-methylenedioxy-, the 3-methoxy-, and the 2-bromo-compounds which do not appear to have been resolved previously. These acids [(Ia–f) and (III)] were converted by the action of cyclohexanone into the corresponding 3-aryl-1,4-dioxaspiro[4,5]decan-2-ones [dioxolanones (IVa–f) and (V)]. Comparisons of the signs of the experimentally observed Cotton effects with those predicted by application of the lactone sector rule give good agreement. The acids were also reduced by aluminium lithium hydride to the corresponding glycols, which yielded when treated with cyclohexanone the 2-aryl-1,4-dioxaspiro[4,5]decanes [dioxolans (Xa, b, and e) and (XI)]. The dioxolan structures provide a skeletal background which shows up more clearly the Cotton effects associated with the lactone keto-group. The changes in o.r.d. characteristics of phenylethylene glycol on successive methylation of the hydroxy-groups were also recorded.