Dithiane ring opening

Two enones of general formula 702 were introduced into reaction with NCN binucleophiles, namely, 768 [453] and 769 [475] (Scheme 152). In case of 768, one of the ethoxy groups can be retained in the final strucmre. Reactions with 769 were accompanied with the dithiane ring opening to give thiols 771. 

Pyridyl-l,3-dithianes (50) result from the reaction of picolyl lithium reagents with 1,2-dithiolanes in the presence of HMPT. An initial ring opening is followed by reaction at the carbanion site with a second mole of dithiolane <96PS(112)101>. 

The stability of substituted 1,2-dithianes toward ring-opening polymerization was tested by heating the disulfides with a catalytic amount of sodium methanethiolate <1989T91> none of the 1,2-dithianes were stable with respect to polymerization under these conditions. The thermal polymerization of 1,2-dithiane was also studied in detail <2005POJ512, 2004MM3143>. 

With Dithiane. Dithiane is one of the most popular functionalized carbanion used for the ring opening of epoxides. This reaction has been studied by different groups [31,56], The anion of bis(phenylthio)methane has been successfully used for the opening of epoxides derived from furanose [56]. This method is an excellent way to prepare formyl derivatives that are suitable for chain extension by olefination. Alternatively formyl derivatives can be reduced to hydroxymethyl derivatives. A recent application of epoxide 33... 

Rhodium-catalysed decomposition of methyl diazoacetate (1.2 equiv.) in the presence of 1,3-dithiolane yields mainly dithiane (31) as a mixture of diastereoisomers.34 Ring-expanded product (32) and ring-opened products (33) arising from a second condensation of the carbene are also isolated, albeit in low yield. Similar reactivity is observed with 1,3-oxathiolane. 

Dithianes are ring opened by organolithium reagents and subsequent reaction with electrophiles provides unsymmetrically substituted dithia compounds (95JCS(P1)2381). 

The ability of sulfur to stabilize an adjacent anion will be discussed in Chapter 46, and it means that sulfur heterocycles are much easier to deprotonate than THF. The most important of these contains two sulfur atoms dithiane. Deprotonation of dithiane occurs in between the two heteroatoms, and you can see some chemistry that arises from this on p. 1234. For tire moment, we will just show you series of reactions that illustrate nicely both dithiane chemistry and the ring opening of oxygen heterocycles in the presence of BF3, This substituted derivative of dithiane is deprotonated by BuLi in the same way to give a nucleophilic organolithium that will... 

The ring opening of enantiopure IV-tosyl aziridines 215 with 2-substituted 2-lithio-l,3-dithianes takes place at the less substituted carbon atom in good yields (59-92%)321. The corresponding adducts gave /9-tosylamino carbonyl compounds after reaction with methyl iodide under acetone reflux. 

Nucleophilic attack by azide anion on bicyclic sulfonium salt 278 kinetically favors ring opening to give a nine-membered a-azidosulfide 280, while 2-(3 -azidopropyl)-l,3-dithiane 279 is the thermodynamic product (Equation 38) <2003TL2841>. 

The anion 117 prepared by deprotonation of the carbene complex [Cr(CO)s C(OEt)CH2CHS(CH2)3S ] (116) also rearranges spontaneously by carbonyl insertion to give a neutral six-membered chelate (118) after alkylation. The analogous tungsten carbene complex affords stereoselec-tively a vinylcarbene complex (119) by opening of the 1,3-dithiane ring (705). Reaction of 118 with methyl hydrazine produces mainly an NMe- or... 

In the laboratory of D.R. Williams, a carbanion methodology for the alkylations and acylations of substituted oxazoles was investigated. The study showed that the monoalkylation of the dianion generated from 2-(5-oxazolyl)-1,3-dithiane exclusively led to the substitution of the carbon adjacent to sulfur. However, acylation reactions of the dianion afforded 4,5-disubstituted oxazoles. These new products presumably arose from carbonyinitrile ylide intermediates, which were generated by the selective C-acylation of a ring-opened dianion tautomer. This is the first example of a base-induced, low-temperature Cornforth rearrangement. 

Epoxide28 2 6.278.300 gnj oxirane288 ring opening by 2-lithio-1,3-dithianes requires the use of low temperatures (-20 to 0 C), since these organometallics are not sufficiently stable in THF at higher temperatures. Under these conditions the reaction is often slow (1 or 2 h) and requires in some cases 1 or even 2 days to go to completion (Scheme 58, entry b Scheme 62 Scheme 66 Scheme 67).2 .296.29 ... 

Finally, although 2-lithio-l,3-dithianes do not usually react with tetrahydrofurans, an intramolecular ring opening of such heterocycles has been once reported and has been applied to the synthesis of a di-thiane derived from a functionalized cyclohexanone (Scheme 67). 7,29S... 

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