Solvent effects conjugate additions

The effect of the solvent on the product distribution is observed in the conjugate addition of amines to 1-bromo-l-(phenylsulfonyl)alkenes (54) (equation 54)46. When the reaction is conducted in benzene at room temperature for 4 days, the adduct 55 is formed in good yield. On the other hand, the reaction in DMSO at 80-90 °C for 2.5 h affords 2-(phenylsulfonyl)aziridines (56) and no adduct (55) is isolated. 

In choosing a solvent, consideration must be given not only to its possible effects upon the absorbing system. Quite generally, polar solvents tend to obliterate spectral fine structure arising from vibrational effects. In addition, the positions of absorption maxima are influenced by nature of the solvent. n Tt and transitions show electronic spectra with conjugated ti electrons in the UV region at about 300-350 nm (B band) and in the visible portion at 500-600 nm. 

Conjugate addition of nitroalkanes to enones.5 This addition can be effected with basic alumina in the absence of a solvent at 25° in 50-88% yield. 

The effect of a remote substituent on the facial selectivities in a nucleophilic conjugate addition has been investigated for the reaction of EtSH with a series of dibenzobicyclo[2.2.2]octatrienes (84). Syn-addition proved to be favoured for nitro substituent and polar solvents increased the selectivity (Table 5).19... 

Unsaturated-d-lactones.1 This reagent undergoes conjugate addition to alkyl vinyl ketones in the presence of catalysts such as diisopropylamine, DBU, and various phosphines, particularly tri-n-butylphosphine. DMSO is the best solvent DMF and C H, CN are only slightly less effective. The products are precursors to a,/ -unsaturated-Mactones. 

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