2-Ethoxycarbonyl-l 3-dithiane

Ethoxycarbonyl-l,3-dithiane (183), easily accessible from ethyl glyoxylate diethyl acetal, can be lithiated-alkylated to afford, after deprotection, a-ketoesters as exemplifies the product 184 (Scheme 53)237. This methodology has been used in the preparation of 3-deoxy-D-manno-2-octulosonic acid (KDO) derivatives238 and of the ABC ring system of manzamine A239. 

Derivatives of unsaturated sugars have been used as starting materials for the synthesis of a number of branched-chain sugars. Pyranosidic enones, for example, were shown to undergo 1,4-additions with lithium dimethyl cuprate, vinyl magnesium bromide, and 2-lithio-2-ethoxycarbonyl-l,3-dithiane, with the carbanion adding trans to the glycosidic substituent (Scheme 66). 4,6-Di-O-... 

Several compounds have been prepared by nucleophilic substitution of chlorine in 2-chloro-l,3-dithian with Grignard reagent (RMgBr), malonic esters, and phenols.A mechanism for the de-ethoxycarbonylation of the 2-(l,3-dithianyl)malonates by sodium chloride or sodium ethoxide has been studied. 2-Chlorotetrahydrofuran reacts with nucleophiles such as 2-lithio-2-phenyl-l,3-dithian (326) by three simultaneous mechanisms i.e. substitution, proton abstraction, and electron transfer) to give the products (327)—(330) (Scheme 12)/° When a dithian (331 R = H or COiMe) was treated with a sulphonyl chloride in pyridine, ring-expansion to the 5//-l,4-dithiepin (332) occurred instead of the expected formation of a sulphonate. ... 

The intermediate a-heteosubstituted carbon radicals genraated by reaction of (TMS)3Si" radical with 1,3-dithiane, or A/-(ethoxycarbonyl)-l,3-thiazolidine derivatives, can participate in consecutive intramolecular C—C bond formation reactions in the presence of proximate 1,2-disubstituted double bonds (equation 51). In the presence of terminal double bonds or in an attenpted intermolecular addition of the intermediate... 

Dithian 2-(l-Ethoxycarbonyl-2-oxo-propyl)- E14a/3, 466 [2-(2-Oxo— 1-COOR —propyli-den)—1,3-dithian + Mg R-SOjH]... 

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