1,1’-Vinyl sulfone, nitroalkene addition

Nitroalkenes, vinyl sulfones and vinylphosphonium salts have been shown as good Michael acceptors for 2-lithio-l,3-dithiane derivatives. Nitroalkene sugar derivative 246 has been used as electrophile for the synthesis of branched-chain cyclitols397 - 399. Seebach and Langer studied the addition to simple nitroalkenes using the chiral solvent (,S ,.S )-DDB (247) with some degree of diastereoselectivity400,401. 

Cinchona alkaloids and their derivatives have been reported to catalyse the Michael addition of (V-heterocycles, such as benztriazole, to nitroalkenes in moderate to high enantioselectivities (<94% ee) 15 The thiourea derivative (149) catalysed Michael addition of thioacetic acid to a range of frafts-/f-nitrostyrenes to afford RCH(SAc)- CH2NO2 (<70% ee) 16 The thiourea derivative (149) and its congeners have been identified as efficient organocatalysts for the Michael addition of a-substituted cyano-acetates RCH(CN)C02Et to vinyl sulfones CH2=C(R)S02Ph (72-96% ee) 17 ... 

Acceptor-substituted alkenes that are employed as substrates in Michael additions include a./l-unsaturated ketones (for example, see Figure 10.59), a,/3-unsaturated esters (Figure 10.60), and a,/3-unsaturatcd nitriles (Figure 10.61). The corresponding reaction products are bifunctional compounds with C=0 and/or C=N bonds in positions 1 and 5. Analogous reaction conditions allow Michael additions to vinyl sulfones or nitroalkenes. These reactions lead to sulfones and nitro compounds that carry a C=0 and/or a O N bond at the C4 carbon. 

The cerium(III)-mediated conjugate addition of a difluoromethylphosphonate carbanion to a wide range of aliphatic nitroalkenes,acyclic and cyclic vinyl sulfones,5 and vinyl sulfoxides has been reported recently (Scheme 3.85). 

Two examples of unsupported proline-based catalysts are compounds 88 and 89 (Figure 24.30). Dipeptide 88 was used in water in the presence of NaOH in the addition of ketones to nitroalkenes. The presence of sodium hydroxide additive was crucial for the success of the reaction [109]. Catalyst 89 was designed on the structurally rigid hexahydropyrrolo[2,3]indole skeleton and efficiently catalyzed the enantioselective addition of aldehydes to nitroalkenes both in methanol and water [110]. The same catalyst was also used in the addition of aldehydes to vinyl sulfone followed by reduction with sodium borohydride. In this case water was a better reaction medium than methanol [111]. 

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