E, Zisomers

Reactions with Aldehydes. The sulfonyl-stabilized phosphorane reagent has been used for Wittig alkenation of aldehydes. For example, condensation with isonicotinaldehyde gave the a,p-unsaturated sulfone as a single fisomer in 76% yield (eq 3). It is noteworthy that analogous reaction with (methylsulfonylmethy-lene)triphenylphosphorane produced the corresponding methyl-sulfonyl alkene as a 1 1 mixture of the E/Zisomers. ... 

Methyl-l, 4-hexadiene (mixture of E and Zisomers minor product)... 

Racemic epoxy sulfone derivatives are easily prepared from allyl ethers by reaction with sodium/+toluenesulfinate in the presence of iodine followed by treatment with triethylamine, separation of E and Zisomers, and epoxidation with i BuOOH and /+BuLi in THF (eq 3). ... 

Another chiral vinylogous urethane, 677, played a central role in the synthesis of (- )-652 by Lhommet and co-workers (Scheme 90) (494). This compound prepared from (i )-a-methylbenzylamine (678) (495), was diastereoselectively hydrogenated over platinum oxide to give the amino-ester 679 (de >95%). More significantly, methylation of the anion of 679 under conditions of kinetic control afforded 680 (de ca 98%) in 33% overall yield from the chiral amine (496). Wittig reaction of the aldehyde derivative 681 with the stabilized ylide l-(triphenylphosphoranylidene)-2-heptanone yielded 682 (90%) as a 4 1 mixture of E and Zisomers. When this product... 

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