Homer-Emmons olefination procedur

Reaction of [2- " C]acetone with vinylmagnesium bromide (Figure 6.75, Procedure A) provided 2-methyl-3-[2- " C]buten-2-ol (257), which upon treatment with PBra rearranged to give 3,3-dimethyl[3- " C]allyl bromide (258). The latter was used for the alkylation of ethyl acetoacetate, thereby extending the carbon skeleton of the /3-keto ester by a labeled five-carbon (isoprenyl) unit. The initially formed alkylated intermediate 259 was not isolated but immediately saponified and decarboxylated to give ketone 260. Subsequent Homer-Wadsworth-Emmons olefination and reduction of the separated trans-ester 261 converted 260 into [T- Clgeraniol 12621. 

The synthesis of rrani-[13- C]retinoic acid (265) (Procedure B) may serve as an additional example of the use of an [ " C]acetone-based building block. Homer-Wads-worth-Emmons olefination of [2- C]acetone with methyl diethyl-phosphonoacetate afforded methyl 3-methyl-2-[3- C]butenoate t2631. Upon deprotonation, this coupled with /3-ionylideneacetaldehyde (264) to provide 265. thereby extending the carbon skeleton of 264 again by a labeled five-carbon unit Building block 263 was also shown to be accessible (Procedure C) through Reformatsky synthesis of [2- C]acetone with zinc and... 

A protocol for the two-carbon homologation of esters (350) to o,jS-un-saturated esters (352) has been described by Jamison and Webb. Application of multireactor allowed to cany out three-operations procedure involving the ester (350) reduction, phosphonate (351) deprotonation, and the Homer-Wadsworth-Emmons olefination (Scheme 119). ... 

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