Dichloromethane Activation. Direct Methylenation of Ketones and Aldehydes with CH₂Cl₂ Promoted by Mg/TiCl₄/THF

Abstract

[reaction: see text] This Mg-TiCl4-promoted CH2-transfer reaction of CH2Cl2 represents an extremely simple, practical, and efficient methylenation of a variety of ketones and aldehydes, especially in enolizable or sterically hindered ketones such as 2,2-dimethylcyclohexanone, camphor, and fenchone.

Mechanistic Insights into the One‐Pot Synthesis of Propargylamines from Terminal Alkynes and Amines in Chlorinated Solvents Catalyzed by Gold Compounds and Nanoparticles

“…[14,15] Cr II complexes are able to promote methylene transfer from CH 2 Cl 2 to an alkene (cyclopropanation, but only in 2 % yield) and the direct stoichiometric methynelation of ketones and aldehydes has been recorded for a bimetallic Mg/TiCl 4 /THF system. [15] The heterolytic thermal or photocatalytic degradation of CH 2 Cl 2 to HCl and CO under aerobic conditions has been described for heterogeneous catalysts and chlorocuprate ions. [16] The CÀCl bond activation described here represents an elegant example of the activation of CH 2 Cl 2 , which generates and transfers the methylene fragment catalytically (typically 5 mol % catalyst and amounts as low as 1 mol % for longer reaction times) under mild reaction conditions (50 8C).…”

A Unified Approach for the Enantioselective Synthesis of the Brominated Chamigrene Sesquiterpenes

“…We reasoned that failed olefinations were due to the combination of the extremely hindered neopentyl ketone and the bulkiness of reagents. We thus turned our attention to conditions successful at methylenating highly hindered substrates [20] utilizing dichloromethane as a methylene equivalent in combination with TiCl 4 and Mg 0 . These conditions were sufficient to convert 21 into the doubly unsaturated spirocycle 9 in 43% yield.…”

Total Synthesis of the Marine Diterpenoid Blumiolide C

“…Initial attempts at the installation of this C11-C19 double bond involved the direct methylenation of the ketone derived from 11 by removal of the TBS ether and subsequent oxidation of the resulting secondary hydroxy group. Unfortunately, the conversion of the C11-keto group into the corresponding exocyclic methylene moiety proved to be exceedingly difficult and none of the different olefination methods investigated (Wittig, Tebbe, [18] Nysted, [19] or the Huang [20] reagents) delivered any of the desired olefin. Similar difficulties were encountered by Leumann and co-workers in their synthesis of coraxeniolide A; [6a] however, in the coraxeniolide A system Tebbe methylenation of the C11-keto group in the ninemembered ring was possible if the six-membered ring included a methyl or silyl acetal rather than the natural ester moiety.…”