2-Nitrobenzylidene derivatives, photochemical

Tanasescu and his co-workers88-70 have shown that o-nitrobenzylidene acetals, in chloroform or benzene solution, undergo photochemical transformations when exposed to sunlight. It appears that, under these conditions, an o-nitrobenzylidene derivative (III) may be converted into an isomeric o-nitrosobenzoy lester (IV). Thus, Tanasescu and Macov-ski86 showed that a di-(o-nitrobenzylidene)-dibenzoyl-dulcitol, later shown to be 1,3 4,6-di-(o-nitrobenzylidene)-2,5-dibenzoyl-dulcitol,48 could... 

Scheme II.—Utilization of a 2-Nitrobenzylidene Protecting Group in the Synthesis of Methyl 6-Deoxy-2,3-di-0-/3-D-galactopyranosyl-a-L-galactopyranoside. /3-o-GaIacto-pyranosyl (R ) Substituents Were Introduced by Koenigs-Knorr Syntheses, and the Photochemical Cleavage, at 350 nm, of the 2-Nitrobenzylidene Groups Proceeded Regiospecifi-cally. Yielding, Following Oxidation, a 95% Yield of the 3-Hydroxy-4-(2-nitrobenzoate) Derivative.

Three monoacetals, o-,70 wi-97 and p-nitrobenzylidene-dulcitol,97 have been described, the first being formulated, without proof, as the 3,4-derivative. The only triacetal of dulcitol of which we are aware is a tri-(o-nitrobenzylidene)-dulcitol prepared from the aldehyde and the hexitol using as the condensing agent phosphorus pentoxide,70 instead of 75% sulfuric acid which gives the diacetal already mentioned.48 6 Photochemical transformations of o-nitrobenzylidene acetals are discussed on page 148. 

Collins et al. have reported details of their interesting work on the photochemical rearrangement of 2-nitrobenzylidene acetals. Derivatives of methyl 4,6-0-(2-nitrobenzylidene)glycopyranosides rearranged upon u.v.-irradiation in methanol to give the corresponding 4- and 6-(2-nitrosobenzoates), which were converted into the 4- and 6-(2-nitrobenzoates) on oxidation with trifluoroperacetic acid. 2 Thus, methyl 2,3-di-0-acetyl-4,6-0-(2-nitrobenzylidene)-a- and -jS-D-... 

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