TiCl4-Lewis Acid Mediated Catalyzed System

4 TiCl4-Lewis Acid Mediated Catalyzed System 

The use of Lewis acids in MBH reactions at lower temperature in the presence of an additive furnishes either halo aldol or halo methyl enone as the major product while, at room temperature, the formation of the usual MBH adduct has also been reported. However, recently, Iwamura et al have reported the formation of a hemiacetal through aqueous workup during a boron tribromide promoted MBH reaction of p-nitrobenzaldehyde with cyclohexenone. In an earlier observation, Li et al. reported the formation of an unidentified side product (10%) in the TiC -mediated MBH reaction of p-nitrobenzaldehyde with a,p-cycloalkenone. 

R = Ph, naphth-1-yl, 2-N02Ph, 4-N02Ph, 4-CF3Ph, 4-OMePh, 2-nitrocinnamyl, nonyl r2 = Me, Et 

R = Ph, 4-N02Ph, 4-CiPh, 2-MePh 4-BrPh, 4-FPh, 2-naphthyi, PhCH2 r2 = Et 

R = Ph, 4-BrPh, 4-CIPh, 4-FPh, 4-N02Ph t-Bu, Pent, nonyl, EtOCO, naphth-1-yl, PhCH2, frans2-nitrocinnamyl, 4-Cp3Ph r2 = Me, c-Hex, i-Pr, Ph, 4-MePh 

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