New synthetic approach to atypical retinoids: application of a versatile annulation procedure

A new approach to an atypical retinoid is presented. The C-15 skeleton was built up by exploiting a step-by-step sequence: the C-9 fragment of an intermediate was homologated by reaction with a C-4 phosphorane, and then submitted to a benzannulation reaction. The last two carbon atoms were inserted by a Wittig reaction with the C-2 phosphorane of ethyl bromoacetate. Manipulation of functional groups was then performed.