Sulfinyl oxiranes

Sulfinyl oxiranes 2 can be desulfurized with butyllithium at very low temperature to give oxiranes with retention of configuration as a result of a ligand exchange at sulfur (see also Table 6). However, with a benzylic substituent R1, an excess of butyllithium may at higher temperatures induce an elimination to an allylic alcohol. 

Oxidation of cyclic phosphonoformaldehyde dithioacetal, using the Modena protocol, yields the trans disulfoxide 121 in excellent enantiomeric excess. Then 121, via HWE olefination and oxidation of the double bond has been used for the diastereoselective preparation of spirocyclic his-sulfinyl oxiranes (new versatile intermediates in asymmetric synthesis) [79] (Scheme 37). 

Pradilla et al. have shown that simple p-tolyl vinyl sulfoxides undergo nucleophilic epoxidation with metal alkyl peroxides to give enantiopure sulfinyl oxiranes.138 This process takes place with fair to excellent diastereoselectivities. The same group recently reported the epoxidation of diastereomeric hydroxy vinyl sulfoxides, bearing an additional stereocenter adjacent to the reactive carbon-carbon double bond. Hydroxy vinyl sulfoxides 256 and 258 underwent epoxidation with lithium ferf-butyl peroxide with high anti selectivity. However, when potassium ferf-butyl peroxide was used, only hydroxy vinyl sulfoxide 256 showed anti... 

Vinyl sulfoxides have been converted to sulfinyl oxiranes <1996JOC3586>. Protected hydroxyl substituents can have an effect on the diastereoselectivity <2002JOC8166, 2003JOC4797, 2006JOC1569> (Equation 76). 

It has been reported that the treatment of 25 with sodium t-butyl-hydroperoxide furnished the sulfonyl oxirane 26 as minor product (27%) along with bis-epoxides 27a,b as a 44 55 mixture of diastereoisomers (52%) and 27c as a single isomer (21%). The formation of 27a-c has been rationalized in terms of a Payne rearrangement of the sulfinyl oxiranes 25a anti) and 25b syn) to afford the a,P-unsaturated epoxy ketones 25c and 25d. These epoxy ketones undergo second nucleophilic epoxidation to furnish 27a-c. In this process, 25a experiences a fast Payne rearrangement, whilst 25b would require rotation around Cp-Cyfor a suitable orientation and hence slows down the rearrangement. 

Reaction of A-sulfinyl derivative 162 with oxiranes in the presence of a catalyst such as Et4NBr and LiCl or LiBr gave the cyclocondensation products - 1,2,3-oxathiazolidines 163 (Equation 47) <1996JFC49>. 

Enantiopure sulfinyl and sulfonyl oxiranes are versatile synthetic intermediates. Mori and colleagues reported that oxiranyllithium compounds, generated from... 

When chloromethyl p-tolyl sulfoxide (102 R = p-tolyl) is treated with carbonyl compounds (103) and potassium r-butoxide in r-butyl alcohol ether, (p-tolylsulfinyl)oxiranes (104) are directly formed. Chlo-romethyl methyl sulfoxide (102 R = Me) exhibits the same behavior (Scheme 29). These reactions proceed with high stereoselection at the position a to the sulfinyl group. The stereochemical course proposed for the attack of the carbanion of an a-halo sulfoxide on a carbonyl compound is shown in Figure 4. 3... 

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