Bridging the final gap in stereocontrolled Wittig reactions: Methoxymethoxy-armed allylic phosphorus ylides affording conjugated dienes with high cisselectivity

After treatment with an appropriate base (bulyllithium or sodium amide), 2- alkenyltris(2-methoxymethoxyphenyl)phosphonium salts carrying an allyl, cro tyl, or prenyl (3-methyl-2-butenyl) side chain condense with saturated or u nsaturated aldehydes to give conjugated dienes with Z/E ratios ranging from 90:10 to > 99:1 and averaging 96:4. Owing to steric congestion, yields are only moderate ton average 41%; extremes 10-79%). The nonvolatile tris(2-me thoxymethoxyphenyl)phosphine oxide by-product can be readily isolated and r educed to recover the phosphane starting material, or it maybe hydrolyzed t o the water-soluble tris(2-hydroxyphenyl)phosphine oxide.