Cyclopropyl building blocks for organic synthesis, 42. An unprecedented mode of ring opening of methylenecyclopropane moieties - Reactions of methylenecyclopropanecopper reagents with an electrophilic glycine equivalent

Article abstract of DOI:10.1002/jlac.199719971105

The reactions of ethyl 2-acetoxy-2-diphenylmethyleneaminoacetate (1) with organocopper reagents derived from bicyclopropylidene (2) and methylenecyclopropane (3) are accompanied by an unusual mode of opening of one three-membered ring to give 4-methylene-1,2,3,4-tetrahydropyridine derivatives 8a, 9 in good yields. The cuprate derived from methylenespiropentane (4) reacts with 1 to yield both the normal substitution product 14 (37%) as well as the rearrangement product 15 (34%), while the simple cyclopropylcuprate undergoes substitution to give the protected cyclopropylglycine 16 (75%) without rearrangement. The tetrahydropyridine 8a shows an interesting tautomerism in solution. The 4-cyclopropylidenetetrahydropyridine 15 undergoes an unusual dehydrodimerization to produce two separable rotamers, C₂-19 and C₁-19, via 18. Wiley-VCH Verlag GmbH, 1997.