Allylic thiocarbamates rearrangement

While the cyclohexenyl and cycloheptenyl derivatives roc-14aa-14ag and rac-14ba were stable at room temperature, the cyclopentenyl O-allylic thiocarbamates already suffered a partial rearrangement at ambient temperatures [19, 20] while the acyclic O-allylic thiocarbamates showed an intermediate thermal stability. 

Table 2.1.4.12 Pd(0)/BPA-catalyzed rearrangement of racemic acyclic O-allylic thiocarbamates.

The sense and degree of asymmetric induction of the Pd(0)-catalyzed rearrangement of the cyclic and acyclic O-allylic thiocarbamates in the presence of BPA are the same as, or similar to, those in the Pd-catalyzed substitutions of the corresponding cyclic and acyclic racemic allylic carbonates and acetates with sulfinates and thiols. It is therefore proposed that Pd(0)/BPA reacts with the racemic O-allylic thiocarbamate with formation of a jt-allyl-Pd(II) complex, which contains as counter ion the corresponding thiocarbamate ion (Scheme 2.1.4.19) [23, 24]. Substitution of the jt-allyl-Pd(II) complex by the thiocarbamate ion gives the S-allylic thiocarbamate and the Pd catalyst. 

Similar transformations can be achieved from y-methylthioallyl thiocarbamates or from allyl thio-carbamates (Scheme 32, entries c and d). Both reaction sequences take advantage of the easy sigma-tropic rearrangement of allyl thiocarbamates. Furthermore, -methoxyallyl thiocarbamates have played the role of an acetone enolate (Scheme 32, entry a). - ... 

Gais and Bdhme reported that Pd(0)-catalyzed enantioselective 0,5-rearrangement of the racemic O-allylic thiocarbamate 614 using Pd(0) and Trost L-1 as a chiral ligand provided the 5-allylic thiocarbamate 615 in 92% yield with 91 %... 

The palladium(0)-catalysed rearrangement of 0-allylic thiocarbamates in the presence of a chiral bisphosphane has been shown to proceed quantitatively to yield 5 -allylic thiocarbamates in high yield, while it has been reported that treatment of allylic alcohols with thiophosgene and pyridine gave thiolo chloroformates (104) directly, presumably via a rapid [3,3]-sigmatropic rearrangement of initially formed thiono chloroformates (103). 

Allylic thiocarbamates (145) are available from ketones by sequential condensation with vinyl-lithium species and dimethylthiocarbamoyl chloride followed by a [3,3] sigmatropic rearrangement. It has now been shown that these can be used as precursors to a,jS-unsaturated esters by bis-sulphenylation and mercury(ii)-promoted hydrolysis (Scheme 39). Only the B-isomers are produced when the final product (146) is unsubstituted i.e. = H) or carries an a-methyl... 

The Pd-catalyzed allylic alkylation of sulfinate ions, thiols, and thiocarboxylate ions with racemic cyclic and acyclic allylic esters in the presence of bisphosphane BPA generally provides for an efficient asymmetric synthesis of allylic sulfones, sulfides, and thioesters. The Pd-catalyzed rearrangements of allylic sulfinates and allylic O-thiocarbamates, both of which proceed very efficiently in the presence of BPA, are attractive alternative ways to the asymmetric synthesis of allylic sulfones and allyUc thioesters also starting from the corresponding racemic alcohols. 

Palladium(ll) catalysis is also effective for the rearrangement of alkyl allyl A-aryldithiocar-bimidates to alkyl Ar-allyl A-aryldithiocarbamates65 (see Table 5, entry 5) or 0-alkyl S-allyl iminothiocarbonatcs to 0-alkyl /V-allylthiocarbamates5,64. Only poor diastereoselectivity (3-5% de) was obtained in the palladium(II)-eatalyzed rearrangement of S-allyl-0-[(—)-menthyl]-iminothiocarbonate64 to the thiocarbamate (see Table 5. entry 1). 

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