[Rh2(OCOCF3)4] as an auxiliary chromophore in chiroptical studies on steroidal alcohols

The circular dichroism (CD) of in situ formed complexes of steroidal substituted secondary and tertiary alcohols with [Rh-2(OCOCF3)(4)] have been investigated. The applicability of the bulkiness rule, developed for unsubstituted 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 tertiary alcohols containing a double bond, alkoxy, ester or amide groups, halogen substituents as well as additional primary hydroxy groups in a molecule. The influence of other substituents present at the stereogenic center, e.g. a keto-, amino-, azido- or additional hydroxy groups, on CD is also described. It is demonstrated that alcohol molecules bind to the Rh-core at axial positions to form 1:2 adducts of the general formula [Rh-2(OCOCF3)(4)(alcohol)(2)]. (C) 1999 Elsevier Science Ltd. All rights reserved.