Titanium trichloride nitro compounds

Titanous chloride (titanium trichloride) is applied in aqueous solutions, sometimes in the presence of solvents increasing the miscibility of organic compounds with the aqueous phase [199, 200]. Its applications are reduction of nitro compounds [201] and cleavage of nitrogen-nitrogen bonds [202] but it is also an excellent reagent for deoxygenation of sulfoxides [203] and amine oxides [199] (Procedure 38, p. 214). 

Although primary and secondary nitro compounds may be converted, respectively, to aldehydes and ketones by consecutive treatment with alkalis and sulfuric acid (Nef s reaction) the same products can be obtained by reduction with titanium trichloride (yields 45-90%) [565] or chromous chloride (yields 32-77%) [190]. The reaction seems to proceed through a nitroso rather than an aci-nitro intermediate [565] (Scheme 54, route b). 

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). 

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