Tebbe alkenylation

Tebbe, Petasis, and alternative alkenylations Pyrolysis of lactones... 

Tebbe, Petasis and Alternative Alkenylations Methylene-de-oxo-bisubstitution... 

The formation of allyltitanium complexes via the reaction of alkenyl chlorides with the Tebbe reagent has been reported (Scheme 535), through a mechanism involving a [2 + 2]-cycloaddition followed by / -elimination of chloride.1422 1423... 

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). ... 

A limitation of the methylenation of carboxylic acid derivatives with Tebbe-type reagents such as 3 and 11 is that highly electrophilic acid anhydrides and acid halides cannot be transformed to the corresponding enol esters or alkenyl halides. The reaction of titanocene-methylidene generated from 11 with add chlorides results in the formation of acylation products via titanium enolates 12 [44] rather than methylenation. Since the titanium enolates 12 are stable and do not isomerize to the more highly substituted enolates, they are useful for regioselective aldol reactions (Scheme 4.11) [44a]. Although similar titanium enolates are also produced... 

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