A- benzylidene

A benzylidene acetal is a commonly used protective group for 1,2- and 1,3-diols. In the case of a 1,2,3-triol the 1,3-acetal is the preferred product. It has the advantage that it can be removed under neutral conditions by hydrogenolysis or by acid hydrolysis. Benzyl groups and isolated olefins have been hydrogenated in the presence of 1,3-benzylidene acetals. Benzylidene acetals of 1,2-diols are more susceptible to hydrogenolysis than are those of 1,3-diols. In fact, the former can be removed in the presence of the latter. A polymer-bound benzylidene acetal has also been prepared." ... 

Dihydro- -strychnine, C21H24O3N2, m.p. 240-3° (vac.), [a]D38-7/d (CHCI3), forms a methyl ether, m.p. 209° (vac.) and a benzylidene derivative, m.p. 209-215° (Leuehs and Rack, 1940). Unlike -strychnine, the dihydro-derivative can be converted, either by boiling with acetic anhydride or by condensation with malonie acid, into the corresponding 9-acetie acid, in this ease dihydrostrychnine-9-acetie acid, C23H26O4N2, m.p. 300-3° (vac. dec.), 43-0° (H2O) (Leuehs et al., 1942). 

This structure rationalizes (a) the formation of mono- and, under more vigorous conditions, tetra-acetyl derivatives, (b) the methyla-tion to a dimethyl derivative still containing two active hydrogens, (c) the pyrolysis back to monomeric indole, (d) the formation of a benzylidene derivative containing the Ph CH=N— Ar ehromophore, (e) the failure to form a simple nitroso derivative, (f) the Zn/AcOH reduction of the dimethyl trimer to base C18H20N2, shown to be identical with the dihydro derivative of (26). 

The synthesis of the right-wing sector, compound 4, commences with the prochiral diol 26 (see Scheme 4). The latter substance is known and can be conveniently prepared in two steps from diethyl malonate via C-allylation, followed by reduction of the two ethoxy-carbonyl functions. Exposure of 26 to benzaldehyde and a catalytic amount of camphorsulfonic acid (CSA) under dehydrating conditions accomplishes the simultaneous protection of both hydroxyl groups in the form of a benzylidene acetal (see intermediate 32, Scheme 4). Interestingly, when benzylidene acetal 32 is treated with lithium aluminum hydride and aluminum trichloride (1 4) in ether at 25 °C, a Lewis acid induced reduction takes place to give... 

The method described above may be used for the preparation of a wide variety of butenolides substituted in the arylidene ring with either electron-withdrawing or electron-releasing substituents. y-Lactones such as a-benzylidene-7-phenyl-A 1 -bu-tenolide are isoelectronic with azlactones, but have received much less attention. Like the azlactone ring, the butenolide ring may be opened readily by water, alcohols, or amines to form keto acids, keto esters, or keto amides.7 a,-Benzylidene-7-phenyl-A3,1 -butenolide is smoothly isomerized by aluminum chloride to 4-phenyl-2-naphthoic acid in 65-75% yield via intramolecular alkylation. 

ESTER, 43, 100 BenzOpyrazole, 43, 69 3-Benzoylpropionic acid, condensation with benzaldehyde to give a-benzylidene-y-phenyl-A t-bu-tenolide, 43, 3... 

Die Elektrolyse von 6-Brom(Jod)-l-phenyl-hexin-(l) liefert u.a. Benzyliden-cydopro-pan (max. 24% d.Th.)5. 

Morpholino-2-quinoxalinecarbohydrazide (119) gave A( -benzylidene-3-mor-pholino-2-quinoxalinecarbohydrazide (120) (PhCHO, PhH, reflux, H2O removal, 15 h 92% analogs likewise). ... 

A -Benzylidene-3-morpholino-2-quinoxalinecarbohydrazide (132) gave 3-mor-pholino-Al-(4-oxo-2-phenylthiadiazolidin-3-yl)-2-qumoxalinecarboxamide (133) (HSCH2CO2H, PbH, reflux, H2O removal, 15 h 69% analogs similarly)... 

These sunscreen ingredients include octyl-dimethyl-PABA (UVB), 2-ethylhexyl-p-meth-oxycinnamate (UVB),octocrylene (UVA/UVB), octyl salicylate (UVB), benzophenones (UVB/ UVA), and methyl anthranilate (UVA). Avoben-zone or Parsol 1789 and mexoryl, a benzylidene camphor, block UVA. Mexoryl is the most efficient of the UVA organic sunscreens [10]. Many sunscreen formulations combine ingredients to maximize photoprotection. 

The disaccharide derivatives 196 and 197 of N-tosyl-L-serine, of interest for the study of D-galactose-binding lectins, were prepared by Kaifu and Osawa148 from 194 and 195, respectively, by protection of 0-4 and -6 with a benzylidene group, condensation of the acetal with tetra-O-acetyl-a-D-galactopyranosyl bromide (110) under Koenigs-Knorr conditions, and deprotection. 

Benzophenone, conversion to ethyl /S-hydroxy-0,0-diphenylpro-pionate, 44, 57 Benzophenone oxime, 44, 52 Benzopyrazole, 42, 69 3-Benzoylpropionic add, condensation with benzaldehyde to give a-benzylidene-y-phenyl-A y -bu-tenolide, 43, 3 N-Benzylacetamide, 42,18 n-Benzyiacrylamide, 42,16 Benzyl alcohol, reaction with acrylonitrile, 42,16... 

Several reactions of imines of synthetic utility are reported. Nitric oxide reacts with A-benzylidene-4-methoxyaniline (18) in ether to give 4-methoxybenzenediazonium nitrate (19) and benzaldehyde. Two mechanisms are proposed, both involving nitrosodiazene (20), and the preferred route is suggested to involve direct electrophilic reaction of NO to the imine double bond, favoured by the polarity of the latter. 

L-Iditol (sorbi6rite), the last of the four naturally occurring hexitols, occurs in service berries along with sorbitol. After removing sorbitol from the juice by fermentation to L-sorbose with the sorbose bacterium, Acetobacter xylinum, the n-iditol is crystallized as a benzylidene derivative. It has been prepared by the action of sodium amalgam on... 

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