Formation of a-benzylidene derivative

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 structure of colorless deoxyvomicine (CCXLII) follows from (a) ozonolysis, which gives acetaldehyde in high yield (b) the easy formation of a benzylidene derivative, in accord with a CH2 group at C-ll (197) and (c) the UV-spectrum, which is similar to that of vomicine, showing that there is no double bond in conjugation with the Na lactam system (201, 202). 

Reaction of 4-benzylidene-l-phenylpyrrolidine-2,3,5-trione 56 with thiourea 28 occurs with hydrolysis of the amino group and leads to the formation ofl,4-dihydropyrrolo[3,4-J][l,3]thiazine-2,5,7-trione 57 [65] (Scheme 3.17). There is just one reference to the formation of a dihydrothiazine derivative 59 in the reaction of thiourea with an unsaturated ketone 58 under basic catalysis [68] (Scheme 3.18). 

Studies in the field of tetracyclic and pentacycMc triterpenes [gsa] show that the dissociation constants for C 3)-cyanohydrins vary with structural changes even in rings C and D. A comparison with kinetic data for formation of 2-benzylidene derivatives of the same ketones cf. p. 178) indicates that the effect is largely one of conformational transmission. 

Scheme 7 shows formation of a new fused ring described by Mohan and Kataria <1998IJB819>. These authors reported that treatment of the benzylidene compound 19 with hydrazine hydrate in acetic acid in the presence of sodium acetate gave the tricyclic fused pyrazoline derivative 20 in acceptable yield (61%). The two hydrogen atoms at the site of the ring closure were found to be as. 

Treatment of the tungsten complex [W(=C=C=CPh2)(CO)5[ with benzylidene-isopropylimine gives rise to the formation of the azetidinylidene derivative 41 through a formal [2 + 2] cycloaddition between the Co =Cp moiety and the iminic... 

Efforts to cause the carbon nucleophile available at C-2 (carbohydrate numbering) of the osulose derivative 66 to displace the methoxy group with allylic rearrangement and with consequent formation of a tricyclic product by use of Pd(0) catalysts [34] were unsuccessful, but the intended reaction proceeds "smoothly when tin(IV) chloride is used together with acetic anhydride in dichloromethane. Clearly, the Lewis acid activates the allylic ether group, and the C-2 nucleophile effects its displacement. Concurrently, acetolysis of the benzylidene ring occurs and the product isolated is the cu-decalin analogue 67 [33],... 

Benzylidene acetals can be oxidatively cleaved by jV-bromosuccinimide (NBS) to give 6-bromo-4-benzoyl-hexopyranosides (see Chapter 3). This reaction has also been performed on 1,2-0-benzylidene derivatives and it appears that the cleavage reactions result in the formation of a derivative that has an axial benzoyl ester.33... 

The formation of a cyclohexyloxyl radical via 6-exo-trig manner is promoted by the rigid bicyclic structure derived from the sugar benzylidene group (eq. 3.57a). Moreover, eq. 3.57b indicates that radical ring closure to a formyl group is preferable to that onto an olefinic group. 

The high stereoselectivity observed in this cyclization reaction was attributed to the location of the carbonyl moiety in a rigid cyclic ring framework, allowing H-abstraction from the same face of the initially formed five-membered ring. The same group has further utilized the constraint imparted by the benzylidene acetal moiety on the excited state photoreactivity of the carbonyl moiety of the D-xylose derivative 52. Thus, 8-H-abstraction results in the formation of a diastereomeric mixture of cyclized product 53, which is further transformed into D-glucopyranose 54 and D-idopyranose 55 derivatives, as shown in Scheme 8.16 [17]. 

Hydroxylation of the acetamido derivative 96 proceeded67 with the formation of a complex mixture, from which methyl 4-acetamido-6,8-0-benzylidene-4-deoxy-D-tZireo-L-goZacto-octonate (137) was... 

Enyne derived from ditosyl o-phenylenediamine 257 formed in the presence of benzylidene ruthenium carbene complex a nine-membered ring 258 in 5% yield (Equation 30) <20000L543, 2001S654>. Dimerization was a major by-process (22% yield) along with formation of a small amount of 259 (5% yield), which was explained by /3-hydride elimination from the intermediary ruthenacyclobutane. 

Reactions of Enols and Enolate Anions.—Several methods are described for transposition of an oxo-function to the adjacent site. They involve formation of a suitable a-substituted derivative (hydroxymethylene ° or benzylidene ) and subsequent steps which transform the substituent into an isolated oxo-group. Condensations leading to both the 2-hydroxymethylene- and the 2-arylidene-3-oxo-steroids are described for 3-ketones of the 5jS-series, and also of the 5j8,9j5,10a-( retro ) series.Condensations of aromatic aldehydes at C-2 in the 5 -series are unusually slow enolisation towards C-4 is preferred, but steric compression between C-4 and C-6 in 5/3-compounds severely hinders the condensation reaction at C-4, allowing reaction at C-2 via the 2-enol. Reduction of a 21-hydroxymethylene-pregnan-20-one (337) with sodium borohydride afforded the homopregnanediol (338), although reduction of enolised P-dicarbonyl compounds frequently proceeds via elimination to give enones, and thence allylic alcohols. 

The reaction of the benzylidene derivative of 5-methyl-6-thioxo-5,6,ll,12-tetrahydrodibenzo[fe,/]azocin-12-one (63) with hydroxylamine has been found to initiate a novel rearrangement to yield the hydroximinoisothiochromene (64), while the mechanism shown in Scheme 24 has been invoked " to explain the formation of 2,3,4,4a-tetrahydropyrrolo[2,l-fc]quinazolin-9(l//)-one-l-carboxylic acids from the treatment of 1,10,11,11 a-tetrahydropyrrolo [2,1 -c] [ 1,4]benzodiazepin-5,11 -diones (65) with concentrated hydrochloric acid. De Lucca has discovered that hexahydro-... 

Hydrazinoquinoxalines are readily converted into hydrazones on treatment with aldehydes or ketones. Attempted formation of the ben-zylidene derivative 4 gives the benzoyl compound 3, presumably as a result of the ready aerial oxidation of the benzylidene derivative." ... 

Oxidation of benzylidene acetals. Deslongchamps has extended his studies on ozonization of acetals to benzylidene acetals. Ozonization of the benzyhdene derivatives (1) of 9/3,lOa-decalin-20,3 -diol in acetic anhydride containing sodium acetate results in formation of a single product (2) with an axial benzoate group and an equatorial acetate group. This is the same isomer that is obtained from the hemiortho ester (3) thus (3) or an equivalent substance is a probable intermediate in the ozonolysis of (1). 

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