1,3-Dithiane reaction with chlorine

An abnormal (tele) substitution of chlorine in both 2,3- and 2,6-dichloropyrazines 91, 92 occurred on reaction with dithiane anion, while morpholine gave the normal //wo-substitution <06TL31>. Another paper described the highly selective ipso monosubstitution of the 2,3-dichloro compound by enolates in toluene <06T9919>. 

Danishefsky s total synthesis of 317 and its chlorine free precursor monocillin I 316 features an RCM reaction with a substrate 310 that in addition to a dithiane protective group contains a vinyl epoxide and a diene moiety at... 

Chlorinated ketals 221 were lithiated using a catalytic amount (8%) of naphthalene in THE at —78°C to generate the corresponding masked lithium 5-enolates 222, which upon treatment with different electrophiles in THE at temperatures ranging between —78 and 20 °C, and final hydrolysis with water, afforded protected functionalized ketals 223 (Scheme 76). The application of this methodology to the chlorinated dithiane 224, under the same reaction conditions, gave the intermediate 225 and finally products 226 (Scheme 76) -... 

Reaction of 2-substituted-1,3-dithianes with sulfuryl chloride in strictly anhydrous conditions gives 1,3-dithienium hydrogen dichlorides, which are extremely hygroscopic and hydrolysable <83CB1739>. Chlorination of 1,3-dithianes at the C-2 position occurs with common sources of electrophilic chlorine such as sulfuryl chloride or NCS, presumably through initial chlorination at sulfur and Pummerer-type rearrangement (Scheme 25a) <94JOCl672>. 

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