Homer olefination

Reviews have featured epoxidation, cyclopropanation, aziridination, olefination, and rearrangement reactions of asymmetric ylides 66 non-phosphorus stabilized carbanions in alkene synthesis 67 phosphorus ylides and related compounds 68 the Wittig reaction 69,70 and [2,3]-Wittig rearrangement of a-phosphonylated sulfonium and ammonium ylides.71 Reactions of carbanions with electrophilic reagents, including alkylation and Wittig-Homer olefination reactions, have been discussed with reference to Hammett per correlations.72... 

Tandem Michael addition and Homer olefination occur when a-phosphorylvinyl sulfoxides react with salicylaldehyde leading to a 3-sulfinyl-277-l-benzopyran. Any optical activity associated with the vinyl sulfoxide is retained in the product <06JOC8818>. 

A major review of stereocontrol in organic synthesis using the diphenylphos-phoryl group has appeared and includes coverage of Homer olefination and other reactions of phosphine oxide-stabilised carbanions. ... 

Z, 6 )-a-Famesene (204) has been prepared by Homer olefination of methyl vinyl ketone with the phosphine oxide (202) (Scheme 27). The nature of the base used has a large effect on the yield and the authors report that it is more efficient to carry out the elimination step directly with the mixture of diastereo-... 

Dimethyl (2/ ,3 )-tartrate provides the central C4 building block. Homer olefination is used to attach the C2 building block at one end. Asymmetric Sharpless epoxidation converts the resulting olefin to the Cg epoxide. The Cn chain, produced from the Cg and C3 building blocks, is attached at the other end. The missing Ci atom is provided by CH2N2 an Arndt-Eistert reaction leads, via the Cxg diazo ketone, to the Cjg hydroxycarboxylic acid. Cycliza-tion of the seco-isomer gives enf-100 Scheme 52). 

Scheme 54. Characterization of a Synthesis of 100, with Formation of a Open-Chain Intermediate with Terminal Vinyl Groups, Accessible by Homer Olefination of a C Phos-phonate and a C7 Aldehyde. The aldehyde is formed from an achiral educt bv asvrnmetric...

Interestingly, a phosphine oxide was used as a reagent in a Wittig-Homer olefination aiming at the synthesis of the key intermediate of vitamin D3... 

Cyclic (hetero- and carbocyclic) vinyl sulfoxides have been prepared by a tandem Michael addition/Homer olefination reaction of a-phosphorylvinyl sulfoxides and carbonyl compounds bearing a nucleophilic center. Using optically active a-phosphorylvinyl sulfoxides a series of enantiomeric cyclic vinyl sulfoxides in which the chiral sulfinyl group is bonded to a chromene, pyrrazolyne, quinoline or cyclopen-tene ring, has been obtained. The H-W-E reaction of aldehydes with sulfinimine-derived 3-oxo pyrrolidine phosphonates (228) represents a new method for the asymmetric synthesis of ring-functionalized cw-2,5-disubstituted 3-oxo pyrrolidines (229) (Scheme 90). ... 

Synthetic analogues have been prepared as exemplified in Scheme 14 [95]. A first Wittig-Homer olefination of aldehyde 107, followed by acidic treatment, generates cyclohexenone 108. Chemo- and stereoselective reduction of the latter with 9-BBN followed by sy -selective epoxidation of the allylic alcohol (lateral hydroxyl group control) by w-chloroperbenzoic acid gives 109. Selective tosylation of its secondary alcohol moiety (steric hindrance makes the tosylation of the tertiary alcoholic moiety difficult) and subsequent deprotonation of the tertiary alcohol with NaH provide an alcoholate that undergoes an intramolecular displacement reaction. 

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