THE STEREOSELECTIVE PREPARATION OF AN ENANTIOMERICALLY PURE CYCLOPENTANE USING INTRAMOLECULAR ALDOL CYCLOPENTAANNULATION OF A GLUCOSE DERIVATIVE

Methods for the annulation of carbohydrates have found extensive appli cations in organic synthesis. We report here a new protocol for the st ereoselective conversion of glucose into an enantiomerically pure cycl opentane aldehyde 22. The readily available epoxide 15 was reacted wit h allyl Grignard to produce alcohol 16 in 86% yield. Swern oxidation f ollowed by epimerization using triethylamine in N,N-dimethylformamide furnished the ketone 17 also in 86% yield. Regioselective deprotonatio n with lithium hexamethyldisilazane in THF was followed by methylation with methyl iodide and 1,3-dimethyl-3,4,5,6-tetrahydro-2(1H)-pyrimido ne as cosolvent to give 80% yield of ketone 18. Oxidation of ketone 18 by the Wacker procedure gave the 1,4-diketone 19 in 56% yield. Intram olecular aldol condensation occurred readily on treatment of diketone 19 with potassium tert-butoxide in toluene to furnish a 90% yield of e none 20. Treatment with N-bromosuccinimide produced the bromoester 21 in 72% yield, which was reduced to a mixture of aldehydes 22 (61%) and 23 (14%) with zinc shot in 2-propanol.