Titanium trichloride carbonyl compounds

After investigating the reaction in order to control its stereochemistry, they succeeded in improving this approach considerably, as shown below. Introduction of a nitro group into the known styrene 302 by reaction with silver nitrite in the presence of iodine, gave the nitrostyrene 303 in 72% yield. Heating of 303 at 120°C gave the cis-fused adduct 304 stereoselecti-vely in 97% yield. Treatment of the nitro compound 304 thus obtained with titanium trichloride furnished the sensitive ketone 305. Concomitant reduction of the carbonyl and urethane groups of the crude product with LAH afforded ( )-chelidonine in 54% yield from 304 (146) (Scheme 111). 

Generation of Phosphorus Ylides and Phosphonate Anions. NaHMDS isthemostutiUzedbaseforthedeprotonation of a variety of phosphonium salts to generate the corresponding ylides, which then undergo Wittig reaction with a carbonyl compound. More recently, it was shown that such a base is compatible with a variety of other systems. For instance, it was shown that allenes and dienes could be prepared, respectively, from aromatic and alicyclic aldehydes when reacted with (Me2N)3P=CH2 in the presence of 4 equiv of NaHMDS and titanium trichloride iso-propoxide (eqs 30 and 31). ... 

A titanium(Il) species formed from titanium trichloride and lithium aluminum hydride is a useful reagent for the reductive coupling of carbonyl compounds to olefins (McMurry, 1974 McMurry and Fleming, 1974). Both aliphatic and aromatic ketones can be converted to tetrasubstituted olefins in excellent yields. Reductive dimerization of retinal (CCLXXFV) affords j6-carotene (CCLXXV) in 85% yield. The course of the reaction can be accounted for by assuming pinacol formation followed by loss of titanium dioxide. 

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