Dithiane alcohols rearrangement

The resin-supported carbodiimide 2 (R = Cy), related to the popular solution phase reagent dicyclohexylcarbodiimide (DCC), has been the most successfully employed polymeric carbodiimide of this series, especially in the presence of additives to accelerate the coupling reaction and avoid the acylisourea-unreactive acylurea rearrangement [2]. This carbodiimide has been used for esterification reactions, as exemplified in the reaction of dithiane-containing alcohol 3 with Fmoc-protected valine in the presence of a catalytic amount of N,N-dimethylami-nopyridine (DMAP) to give ester 4 [10] (Scheme 7.1). This polymer-supported reagent 2 (R = Cy) has also been used without any additive in the amidation reaction of 3,4-diaminocyclopentanol scaffolds with 2-(methylsulfanyl)acehc acid [11]. 

The liquid-phase oxidation of 1,3-dithian, and oxidation of alcoholic functional groups in the presence of the 1,3-dithian moiety by the Pfitzner-Moffatt reagent, has been studied. Both cis- and 1,3-dithian 1-A -arylimides (167) were prepared and they rearranged with high stereospecificity. 1,3-Dithian 1-imide 1,3,3-trioxide (168) has been obtained, in excellent yield, by the cleavage of the corresponding A-tosyl compound with Na and... 

Sn2 VersusSN2 Reactionof2-TMS-l,3-Dithiane With Vinyl Epoxides. In 2002 Smith et al. demonstrated that 2-lithio-2-TMS-1,3-dithiane reacts with vinyl epoxides in an Sn2 fashion exclusively, while other, larger silyl dithianes afford mixtures of Sn2 and Sn2 products. Particularly useful, the large 2-lithio-2-triisopropyl-1,3-dithiane provides solely the Sn2 product. Furthermore, it was found that trans epoxides furnish syn products and cis epoxides produced anti products, albeit in modest yields (eq 28). However, under the reaction conditions (THF, HMPA) the TMS group underwent a 1,4-Brook rearrangement to afford a 1 1 mixture of the anticipated homoaUyhc alcohol and the rearranged silyl ether. 

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