[Rh-2(OCOCF3)(4)] as an auxiliary chromophore in chiroptical studies on steroidal alcohols

The circular dichroism (CD) of in situ formed complexes of steroidal substi tuted secondary and tertiary alcohols with [Rh-2(OCOCF3)(4)] have been inve stigated. The applicability of the bulkiness rule, developed for unsubstitu ted secondary alcohols and connecting the sign of the E band at ca. 350 nm with the absolute stereochemistry of an alcohol, is extended to substituted secondary and tertiary alcohols. The rule works well for secondary and ter tiary alcohols containing a double bond, alkoxy, ester or amide groups, hal ogen substituents as well as additional primary hydroxy groups in a molecul e. The influence of other substituents present at the stereogenic center, e .g. a keto-, amino-, azido- or additional hydroxy groups, on CD is also des cribed. It is demonstrated that alcohol molecules bind to the Rh-core at ax ial positions to form 1:2 adducts of the general formula [Rh-2(OCOCF3)(4)(a lcohol)(2)]. (C) 1999 Elsevier Science Ltd. All rights reserved.