Nitroethane, conjugate addition with

Compounds with acidic a-hydrogen were considered as potential nucleophilic donors for the extended 1,6-conjugate system of puupehenone. Nitromethane and nitroethane were reacted with stoichiometric amounts of magnesium methoxide and generated nucleophiles were added to a benzene solution of puupehenone (63). The addition products were then acetylated and purified to give compounds (78) and (79). 

The use of aldehyde enolates for conjugate additions is precluded by competing polymerization and al-dolization processes however, introduction of the OfeCHO moiety is accomplished with aldehyde enolate equivalents. For example, dianions of nitroethanes, e.g. 3-phenylnitroethane (165) or methyl 3-nitropropionate (166), add exclusively in the 1,4-mode to ot,3- nones.,36a-b Similarly, the dianion of 4-nitro-1-butene (167) adds in a 1,4-mode exclusively unlike typical dienolates (Section 1.2.2.2.2) which react at the ot-position, this dianion is formally equivalent to the crotonaldehyde >-enolate (Scheme 64).l36c... 

A highly enantioselective conjugate addition of nitromethane and nitroethane to acyclic enones has been recently achieved using chiral cyclohexanediamine-derived primary amine thiourea 48 (Scheme 2.57) [168], With respect to the electrophile, the reaction shows a broad substrate scope and not only 1-aryl- but also 1-alkyl enones afford the corresponding chiral y-nitroketones with good yields and excellent enantioselectivities (92-99% ee). 

A dihydroquinidine-derived chiral thiourea (DHQD-30), which demonstrated significantly better stereocontrol than other cinchona alkaloids, was utilized in the aza-Henry reaction with nitroalkanes and aldimines by Schaus and coworkers (Scheme 13.8) [26]. The utility of the nitroethane pronucleophile conveniently offers a tertiary stereogenic center in the P-nitroamine product 32. The methodology is also conveniently applicable to novel a,P-unsaturated aliphatic imines 29, which are difficult substrates in asymmetric conjugate addition reactions. Similar reaction conditions can be appHed towards to the use of dimethyl malonates as pronucleophiles that generate adducts in high enantioselectivity, which then convert smoothly into P-amino esters under the Nef conditions. 

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