STEREOSELECTIVE SYNTHESIS OF SUBSTITUTED TETRAHYDROFURANS AND BUTYROLACTONES BY A NEW NICKEL-CATALYZED CARBOZINCATION

2-Iodo- and 2-bromoethyl allyl ethers undergo a highly diastereoselect ive ring closure producing trans-4,5-disubstituted lactols. After oxid ation with m-chloroperbenzoic acid, trans-4,5-disubstituted butyrolact ones art obtained. This one-pot stereoselective approach to trans-4,5- disubstituted butyrolactones (2-furanones) proceeds in satisfactory ov erall yield (45-56 %; > 99% trans) for a range of substituted precurso rs 1 (R(2) = phenyl, n-hexyl or i-propyl). The use of cyclic 2-iodoace tals as precursors for the ring closure leads to new bicyclic heterocy cles, such as 6a and 6b, with high endo-selectivity (> 96% endo). An e ndo-selective preparation of a pyrrolidine is also reported (endo > 96 %), although in this case, the intermediate zinc reagent could only be trapped effiently by deuterolysis, due to its low reactivity.