Open AccessCuᴵᴵ-katalysierte Kupplung von Cyclopropyl-carbenoiden
Author(s) -
M. Borer,
Thomas Loosli,
Markus Neuenschwander
Publication year - 1991
Publication title -
chimia
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.387
H-Index - 55
eISSN - 2673-2424
pISSN - 0009-4293
DOI - 10.2533/chimia.1991.382
Subject(s) - chemistry , catalysis , oxidative coupling of methane , medicinal chemistry , transition metal , scope (computer science) , stereochemistry , sequence (biology) , computational chemistry , coupling (piping) , photochemistry , organic chemistry , materials science , biochemistry , computer science , metallurgy , programming language
Contrary to the reaction of 'Hückel anions' like cyclopentadienide or cyclononatetraenide, treatment of 1-bromo-1-lithio-carbenoids 2 with 1 mol-equiv. of CuCl2 in THF does not result in an oxidative coupling 2 → 8 (see Scheme 2), but in a formal dimerization of two carbenes to give bi(cyclopropylidenes) 10. Reaction parameters influencing the yields are discussed in the case 2a → 10a (R=PhS). Yields of ca. 40% of 10a are obtained under 'kinetic control' at high concentrations of 2a and in THF/Et2O mixtures. Besides CuCl2, which is catalytically active, FeCl3 has been found to be a coupling agent as well, while AgBF4, AgCl, CoF3, and CuCl were inactive in THF. Mixed couplings of two different carbenoids are possible, while diastereoselectivity of the active transition metal complex seems to be low. First experimental results obtained with 2b (R=BuO) and 2c (R=PhCH2) hint at a considerable scope of the sequence 2 → 10.