Oshima-Lombardo reagent

Notes Original report L. Lombardo, Tetrahedron Letters 1982, 23, 4293 Sometimes called the Oshima-Lombardo Reagent. 

Another reagent for the methylenation of aldehydes or ketones is the Oshima-Lombardo reagent TiCl4-Zn-CH2l2 (or CH2Br2). This reagent is non-basic and can therefore be advantageous for base-sensitive substrates (2.105). 

Two additional titanium reagents that have been used for olefination reactions are Cp2TiMc2, developed by Petasis, 25 d Lombardo s use b Oshima s reagent (Zn—CH2Br2—TiCU). Cp2TiMc2 reagent is... 

A drawback of the Tebbe and related reagents is that they are generally suitable only for methylenation and do not permit the formation of higher alkyl analogues. However, the alkenylation of esters (or amides) has been found possible using the Oshima-Lombardo conditions in the presence of TMEDA (tetramethylethylene-diamine) (2.106). This chemistry requires the prior formation of the alkyl gem-dibromide and a more-convenient method, using a dithioacetal, has been reported (2.107). ... 

Indeed, the reproducibility of this method was questioned by Lombardo in 1982 [14]. He attempted to apply Takai and Oshima s procedure to the methylenation of a gibberellin derivative with Zn (pure, without lead)-CH2Br2-TiCl4, but only decomposition of the substrate was observed. Lombardo later demonstrated an improved procedure. According to his report, the requisite ageing period for the preparation of the reagent was three days (Scheme 5.7). 

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