Synlett 2002(3): 0458-0462
DOI: 10.1055/s-2002-20465
LETTER
© Georg Thieme Verlag Stuttgart · New York

Cyclization of Bicyclic Diterpenes Promoted by SmI2. Synthesis of Tri- and Tetracyclic Diterpenes

Isidro S. Marcos*, Rosalina F. Moro, Santiago Carballares M., Julio G. Urones
Dept. de Química Orgánica, Universidad de Salamanca, Plaza de los Caídos 1-5, 37008 Salamanca, Spain
Fax: +34(92)3294574; e-Mail: ismarcos@usal.es;
Further Information

Publication History

Received 28 September 2001
Publication Date:
05 February 2007 (online)

Abstract

The synthesis of 15-hibaen-14-one (a tetracyclic diterpene) is described from zamoranic acid as starting material in an excellent yield and with total control of the stereochemistry. The key step is a SmI2 promoted pinacol cyclization.

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15-Hibaen-14-one(23): Rf = 0.42(Hex/EtOAc 9:1); mp 95-98 ºC; [α]D 20 -33.2 (c 0.5, CHCl3). IR: 2953, 1759, 1177, 721 cm-1. 1H NMR (400 MHz, CDCl3): δ = 6.12 and 5.89 (1 H, d ea, J = 7.0 Hz, H-15 and H-16); 1.94 (1 H, dt, J = 4.7 and 13.3 Hz, H-7); 1.05 (3 H, s, Me-17); 0.87, 0.87 and 0.83 (3 Me, s each, Me-18, Me-19 and Me-20) ppm. 13C NMR (100 MHz, CDCl3): δ = 39.2 (C-1); 18.5 (C-2); 41.7 (C-3); 33.1 (C-4); 54.6 (C-5); 19.0 (C-6); 27.2 (C-7); 55.4 (C-8); 55.9 (C-9); 38.2 (C-10); 18.4 (C-11); 35.3 (C-12); 50.9 (C-13); 220.0 (C-14); 133.0 (C-15); 132.3 (C-16); 16.5 (C-17); 33.5 (C-18); 21.9 (C-19); 15.5 (C-20). Anal. Calcd for C20H30O: C, 83.86; H, 10.56. Found: C, 83.76; H, 10.66.