A Ring Closing Metathesis Based Approach for the Spiroannulation of Cyclopentanes and Cyclohexanes. Formal Synthesis of (±)-Acorones
作者:A. Srikrishna、M. Srinivasa Rao、Santosh J. Gharpure、N. Chandrasekhar Babu
DOI:10.1055/s-2001-18743
日期:——
An efficient ring closing methathesis (RCM) reaction based approach was developed for the spiroannulation of cyclopentanes and cyclohexanes and its utility demonstrated in the formal synthesis of the spirosesquiterpenes acorones.
Spiro[5.5]undecane derivatives 6A and 7S were obtained in moderate stereoselectivity by the intramolecular spiroannelation reaction of a bis-acetal 3 promoted by TMSOTf, and the selectivity was reversed by changing the solvent from acetonitrile to THF.
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).