Reactions of carbenes with ethers: The role of noncovalent interactions

The influence of ethers upon carbenes has been investigated computationally by the B3LYP, MP2, and MPWB1K methods. Ylide formation is only obtained with reactive-electrophilic carbenes like cyclopentadienylidene, whereas more nucleophilic carbenes like cyclopent-2-enylidene associate by interactions of lone pairs of carbon and oxygen atoms with C-H bonds. Between the, stabilized-electrophilic dichlorocarbene and the oxygen lone pairs, only weak complexes are formed. Furthermore, the mechanism of the C-H insertion of dichlorocarbene into bicyclic ethers containing a three-membered ring has been explored. The experimental data confirm the computational results. The insertion occurs easily into the a position of the oxygen atom in secondary ethers but not into the methyl group of methyl ethers. In all cases, insertion into the a-position of a cyclopropane ring is not competitive. ((C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008).