3- sulfinyl-1-alkene 2-alken

In contrast to a, -ethylenic ketones or even a, -ethylenic sulfones, a, ) -ethylenic sulfoxides generally are not sufficiently electrophilic to undergo successful nucleophilic j8-addition . a-Carbonyl-a, j8-ethylenic sulfoxides, however, are potent, doubly activated alkenes which undergo rapid and complete -addition of various types of nucleophiles even at — 78 °C. A brief account summarizing this area is available . The stereochemical outcome of such asymmetric conjugate additions to enantiomerically pure 2-sulfmyl 2-cycloalkenones and 2-sulfinyl-2-alkenolides has been rationalized in terms of a metal-chelated intermediate in which a metal ion locks the -carbonyl sulfoxide into a rigid conformation (36 cf. 33). In this fixed conformation, one diastereoface of the cyclic n... 

The same methodology was successfnUy applied for the preparation of alkynes 152 and alkenes 153 from a-sulfinyl ketones 150 and S-mesyloxy snlfoxides 151, respectively (equation 52). 

Sulfoxides and sulfones can be prepared on cross-linked polystyrene by oxidation of thioethers. The most commonly used reagent for this purpose is MCPBA in DCM [8,12,32,57,80-82] or dioxane [50,83] (Table 8.6), but other oxidants such as H2O2 in acetic acid [34], oxone (Entry 7, Table 8.6), or oxaziridines [84] have also been used. PEG-bound thioethers have been converted into sulfones by oxidation with MCPBA in DCM [52,54] or with Os04/NMO [85], The oxidation of thioethers to sulfoxides requires careful control of the reaction conditions to prevent the formation of sulfones. Sulfones have also been prepared by S-alkylation of polystyrene-bound sulfi-nates (Entries 8 and 9, Table 8.6), by a-alkylation of sulfones (BuLi, THF, alkyl halide [86]), and by addition of sulfinyl radicals to resin-bound alkenes or alkynes (Entry 11, Table 8.6). 

TL 27 5509 (1986) (3-sulfinyl-2-aUcenoate ester) 28 107 (1987) (3-sulfinyl-2-alkenoate ester) 30 3853 (2-suiiinyI-2-a]ken-l-oiie)l 4003 (sulfinyl quinone), 4227 (fumaric diamide), 6973 (2-alkoxycarbonyl-2-alkene-4-lactam), 6977 (2-alkoxycarbonyl-2-alkene-4-lactam) (1989) 32 947 (sulfinyl maleate), 2005 (2-acyl-2-alkenoate ester), 7751 (4-aIkoxy-3-sulfonyl-2-alken-4-olide) (1991)... 

JOC 56 1983 (1991) (sulfinyl maleimide) 574664 (2-cyano-2-alkenoate ester), 6870 (sulfinyl quinone) (1992) 59 1499 (sulfinyl maleate), 2211 (l-nitro-2-suIfinyl-l-alkene), 7774 (2-cyano-2-alkenoate ester) (1994) 60 4962 (1995) (1,1-disuMmyl-l-aIkene)... 

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