SYNTHESIS OF ENANTIOMERICALLY PURE TRANS-1,2-DISUBSTITUTED CYCLOPENTANES AND CYCLOHEXANES BY INTRAMOLECULAR ALLYLSILANE ADDITION TO CHIRAL ALKYLIDENE-1,3-DICARBONYL COMPOUNDS

Enantiomerically pure trans-1,2-disubstituted cyclopentanes 14 and cyc lohexanes 15 bearing three stereogenic centers can be synthesized high ly selectively by Lewis acid induced intramolecular cyclizations of ch iral alkylidene-1,3-dicarbonyl compounds 8 and 9. The best results wer e obtained using SnCl4 and the substrates 8d and 9d, which contain an oxazolidinone moiety derived from (S)-phenylalanine. In these reaction s, 10d was formed from 8d in a 98:1:1 ratio, while 11d was formed from 9d in a 99:1 ratio, both in 87 % yield. The configuration of the majo r products 10d and lid was proven by X-ray analysis. Reduction of 10d and 11d with LiAlH4 led to 14 and 15, respectively, or to the diols 16 and 17. The alkylidene-1,3-dicarbonyl compounds 8 and 9 were synthesi zed by Knoevenagel condensation of the respective allylsilane carbalde hydes 6 and 7 with the malonic acid derivatives 5a-d.