Stereoselective synthesis of substituted tetrahydrofurans and butyrolactones by a new nickel catalyzed carbozincation

Abstract

2-Iodo- and 2-bromoethyl allyl ethers undergo a highly diastereoselective ring closure producing trans-4,5-disubstituted lactols. After oxidation with m-chloroperbenzoic acid, trans-4,5-disubstituted butyrolactones (2-furanones) proceeds in satisfactory overall yield (45–56 %; >99% trans) for a range of substituted precursors 1 (R 2 = phenyl, n-hexyl or i-propyl). The use of cyclic 2-iodoacetals as precursors for the ring closure leads to new bicyclic heterocycles, such as 6a and 6b, with high endo-selectivity (>96% endo). An endo-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.