Synthesis of (−)-Astrogorgiadiol

Reaction of Rh2(S)-PTPA4 with the (R)-citronellol-derived α-diazo-β-ketoester 1 led to the formation of cyclic β-ketoester 2 in 95% yield and 48% diastereomeric excess. The purity of 2 was increased to >99% de after one crystallization. To demonstrate its utility in steroid total synthesis, the β-ketoester 2 was carried on to secosteroid (−)-astrogorgiadiol (3), a naturally occuring vitamin D analogue with antiproliferative properties.