Rearrangement stereospecific

One of the first uses of the allylic sulfoxide-sulfenate interconversion was made by Jones and coworkers64, who reported exclusive suprafacial rearrangement of the allyl group in the steroidal sulfoxide 17 shown in equation 13. Two other examples are shown in equations 1465 and 1566. Evans and coworkers have demonstrated the utility of the suprafacial allylic sulfoxide-sulfenate rearrangement in a new synthesis of the tetracyclic alcohol 24 (equation 16)67, as well as in a synthesis of prostaglandin intermediates as shown in equation 1768. The stereospecific rearrangement of the unstable sulfenate intermediate obtained from the cis diol 25 indicates the suprafacial nature of this process. 

Note that (35) must be the stereoisomer with Ph and Cl trans for the anti-peri-planar arrangement required for the stereospecific rearrangement, and so the GrIgnard addition must be highly stereoseleetive. This all makes sense by con formatlonal analysis. 

The initial C-0 bond cleavage (by attack of a/the bromide ion at the benzylic carbon, followed by recyclization of the intermediate 301 by selective alkylation at sulfur) was suggested to be responsible for a stereospecific rearrangement of 2-substituted-1,3,2 -oxazaphospholidine-2-thiones 299 derived from (-) pseudoephedrine into... 

Scheme 70 Stereospecific rearrangement of 2-substituted- l,3,2-oxazaphospholidine-2-thiones 299...

A new BF3-induced stereospecific rearrangement of the epoxy ethers 68 gave the enantiopure tetrahydro 2-benzoxepin-4-ols 69a, b in generally good yields <06JOC1537>. The enantiomerically enriched compounds 69c,d were also produced. 

NMR spectroscopy was used to study the course of stereospecific rearrangement of cyclic sulfones to cyclic sulfinates. ... 

This stereospecific rearrangement is a key step in a synthesis of optically active 26-hydroxycholesterol and 25,28-dihydroxy-7,8-dihydroergosterol. 

A stereospecific rearrangement is observed in the photolysis of 17j8-hydroxy-4a,5a-epoxy-4(8-methylandrostan-3-one (18) to give the j8-diketone (19)21 the analogous 4/3,5/3-epoxysteroid is converted in the same manner into the diketone with a 5a-methyl group. 

In the Woodward synthesis of prostaglandin (621, intermediate 172 formed in situ from the corresponding amine was smoothly transformed into bicyclic aldehyde 173. Seebach and co-workers (63) have also observed several stereospecific rearrangements using the same reaction. For example, diazotization of amine 174 gave specifically the cis-cyclopentane 175 which was then epimerized into the more stable trans-cyclopentane 176. 

Similarly, Jung and D Amico have shown that chiral tertiary allylic epoxides undergo a stereospecific rearrangement in the presence of BF3-OEt2 to give optically active quaternary aldehydes 74. The stereospecificity of the process is rationalized on the basis of hindered rotation of the intermediate carbocation. Furthermore, eclipsing interactions hinder the... 

The recovered tosylates on the other hand contained more D at C(9) than the isolated acetates (approximately twice as much in the recovered tosylate from the solvolysis of [395] compared with that recovered from the solvolysis of the mixture). These results indicated stereospecific rearrangement via internal return of the tosylate ion pair. 

Other selected reactions of (Re)+ derivatives include the deprotonation of S-bound DMSO, S(CH2R)2 (R = sp or sp C) complexes at the Ca atom that are followed by stereospecific rearrangements the deprotonation/reprotonation of [(Re)-()]2-CH2=CHR)]+ to give [(Re)(=CHCH2R)]+ deprotonation of amine and phosphine derivatives [(Re)(EHR2)] " to the amides and phosphides [(Re)(ER2)] epimerization of secondary alcohols catalyzed by [(Re)-(OMe)] unprecedented transformation of N-bound pyrrolyl to C-bound pyrrolyl species. 

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