Wittig reaction with Corey reagent

After oxidation to the aldehyde trans-(5S)-S6, the latter was reacted with the Wollenberg reagent, 4-lithio-l-methoxybutadiene, to effect a four-carbon chain extension to trans-(5S)-SS. Corey subsequently reported that the use of the Wollenberg reagent was difficult to reproduce, and described an improved procedure using 4-lithio-l-methoxybut-l-en-3-yne. A Wittig reaction with 46 (Scheme 3.19) then yielded LTA4 methyl ester. 

Corey and co-workers " found that when powdered sodium hydride is stirred into excess dimethyl sulfoxide under nitrogen at 65-70° hydrogen is evolved with formation of a solution of the highly reactive sodium methylsulfinyl methylide (1). This salt reacts with ethyltriphenylphosphonium bromide at room temperature to form the Wittig reagent (2), as shown by its rapid reaction with benzophenone to form 1,1-diphenylpropene-l (3). The strongly basic character of methylsulfinyl... 

The presence of halogen atoms in a molecule is compatible with formation of an ylid and subsequent Wittig reaction. Carbon tetrabromide and triphenylphosphine have been used to give vinyl dibromide products, which are rapidly converted to the corresponding alkyne. Indeed, this is an important synthetic route to alkynes called the Corey-Fuchs procedure. The reaction of 511 with this reagent gave vinyl dibromide 512 in 77% yield as part of Marshall s synthesis of callystatin When 512 was treated with butyllithium... 

The synthesis of these compounds was relatively straightforward, the 16- and 17- substituted compounds being prepared by reaction of the appropriate Wittig type reagent with Corey lactone aldehyde intermediates of type 1 and the C-15 methyl compounds via a Grignard reaction of an appropriate ketone. 

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