Stereoselective Henry Reactions and Applications to Organic Synthesis

3 STEREOSELECTIVE HENRY REACTIONS AND APPLICATIONS TO ORGANIC SYNTHESIS 

In general, the Henry reaction proceeds in a non-selective way to give a mixture of anti (erythro) and syn (threo) isomers. Ab initio calculations on the Henry reaction suggest that free nitronate anions (not influenced by cations) react with aldehydes via transition states in which the nitro and carbonyl dipoles are antiperiplanar to each other. This kind of reaction yields anti-nitro alcohols. The Henry reaction between lithium nitronates and aldehydes is predicted to occur via cyclic transition states yielding syn-nitro alcohols as major products (Eq. 3.64).108 

Tetrahydropyranyl (THP)-protected nitroethanol can be doubly deprotonated to lithium a-lithionitronate, which is stable to react with various electrophiles. Higher P-nitro alcohols, 

Nitro compound Aldehyde Condition Product synlanti 

CH3CH2N02 CgHnCHO 1) 2 n-BuLi in THF-HMPA 2) AcOH, -100 °C (Method A) OH Y C5Hh no2 81/19 

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