Lewis Acid-Mediated Stereoselective Spiroannelation: A Facile Access to Aphidicolane and Stemodane B/C/D Ring Systems.

Abstract

A novel and stereoselective spiroannelation reaction was developed. Treatment of the suitably functionalized cyclohexene derivative (3) with trimethylsilyl trifluoromethanesulfonate (TMSOTf) afforded the spiro[5.5]undecanes 4A and 5S exclusively. Changing the solvent from CH2Cl2 to CH3CN or THF increased the stereoselectivity; predominant formation of 4A in CH3CN and 5S in THF was observed. The spirocyclic compounds 4A and 5S were transformed into the tricyclo[6.3.1.01, 6]dodecane derivatives (19A and 27S) corresponding to the B/C/D rings of aphidicolanes (1) and stemodanes (2).