Stereoselectivity thio-Claisen rearrangement

The substrate-controlled stereoselective thio-Claisen rearrangement is... 

Some applications of the thio-Claisen rearrangement to the syntheses of thiocarbonyl compounds, particularly unsaturated dithiocstcrs and thionesters, and of its stereocontrol aspects are reviewed in [120]. A particularly high stereoselectivity was observed with S-allyl derivatives of P-hydroxydithioesters syn products were obtained exclusively, according to the accompanying scheme [495,496]. 

Thioamide-bearing (-F)-traizs-2,5-diphenylpyrrolidine 70 shows high dia-stereoselectivity during the thio-Claisen rearrangement (Eq. 24) [47]. Two... 

The thio-Claisen rearrangement has been successfully used for stereoselective carbon-carbon bond formation. Depending on the substitution of the pericycHc nucleus, two types of stereocontrol can be involved an internal control, closely related to the configurations elements of the heterodiene, or an external control by... 

Similarly, but in the cyclic series, the thio-Claisen rearrangement of substrates derived from chiral thiolactams was reported to be facile but poorly stereoselective [129]. The low stereocontrol observed in both cases may be explained by the lack of facial selectivity resulting from the free rotation around the C-N bond of the N,S-ketene acetals. This critical issue has been solved either by constructing a rigid bicyclic framework or by using C2-symmetric amines as chiral inductors. The former strategy, developed by Meyers et al. [45], involved bicycUc thiolactams, which were transformed into N,S-ketene acetals by deprotonation with LDA, followed by S-allylation with various allyl halides (Scheme 9.27). 

A route to allyl vinyl thioethers with defined E- or Z-geometry at the vinyl double bond has been reported (Scheme 46) the key step is reaction of a vinyl alanate (89) or (90), produced stereoseleCtively, with an allyl thiosulphonate and proceeds with retention of geometry at the alane carbon. The products are potential substrates for thio-Claisen rearrangements. 

Apart from the Cope and Claisen-Cope rearrangements, a number of named reactions are to be found within the category of [3,3] shifts t reactions (6.106)-(6.111) are examples of some of these processes. The thio-Claisen rearrangement the sulphur analogue of reactions (6.106) and (6.107) is also well known. The all carbon atom counterpart of the Claisen rearrangement ((6.106) 0=CH2) was not discovered until it was realized that the final aro-matization step required the presence of a strong base to promote the necessary tautomeric change. In reactions (6.1 07)-(6.111) the influence of steric factors on the stereoselectivity of the reactions is apparent. In reaction (6.109),... 

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