Palladium-catalyzed synthesis of Benzoannulated spiroketal lactones derived from cholesterol: NMR characterization and crystal structures

Abstract

Two new Benzoannulated spiroketal lactones were synthesized by Pd-catalyzed cyclization of derivatives of 2-(6-hydroxyhex-1-yn-1-yl)benzoic acid obtained from cholesterol. Unexpectedly, the Pd-catalyzed spirocyclization led to steroid isochromen-1-ones as major products and only small amounts of the expected spiroketal lactones. The obtained isochromen-1-ones were successfully converted to the desired spiroketal lactones by saponification followed by acidic workup. NMR characterization provided enough evidence on the structure of the obtained compounds. Single crystal x-ray diffraction corroborated the proposed structures.