2-phenyl-4-substituted derivatives, ring

Unlike other diene photopericyclic reactions, cyclohexadiene ring opening proceeds with reasonable efficiency in phenyl-substituted derivatives, although the quantum yields are generally significantly lower than those of non-arylated systems. Two examples of the conversion of 93 to 94 are shown in equation 36178,179... 

The reaction is highly regioselective for substituted cyclic ortho esters, with ring opening mainly at the primary carbon center. However, reversed reactivity is observed for the phenyl-substituted derivative. Corresponding 1,4- and 1,5-diol derivatives are obtained in reaction of six- and seven-membered cyclic ortho esters. 

Numerous papers have been published describing the photochemical production of enones from carbonyl compounds and alkynes. The first detection of an oxetene intermediate involved low-temperature (-78 C) photolysis of 2-butyne and benzaldehyde to form the photoproduct (61), which was observed by NMR. The oxetene undergoes further photoreaction with benzaldehyde to form the novel fused oxetane (62). Recently, Friedrich has reported Either studies on the reactivity of oxetenes and developed alternative syntheses of the parent compound and 3-phenyloxete (64). The parent oxetene is found to have a thermal half-life of t proximately 8 h in solution at room temperature. The phenyl-substituted derivative (64) underwent slow ring-opening under acidic conditions to form 2-phenylprq)enal and air oxidation to yield a formate derivative, probably via a radical process. 

In contrast, cyclobutadiene dianion 38, a. Huckel aromatic compound, was shown calculationally by Schleyer to be — due to coulombic repulsion — far less stable than Y-delocalized spezies with more favorable n charge distributions. This was confirmed by Boche and Thiel Although JS itself could not be prepared until now, phenyl substituted derivatives show no special charge delocalization within the cyclobutadiene ring. 

Many 1-phenylflavazoles derived from sugars have been characterized by chromatographic Rf values " and by x-ray diffraction patterns. " Most syntheses of pyrazolo[3,4-b]quinoxalines involve polyhydroxy-alkylquinoxalines as intermediates and, by reaction with phenylhydrazine, result in the formation of 1-phenyl substituted derivatives of the ring system. Thus the o-arabotetrahydroxybutyl compound 6, obtained from reaction of o-glucose with o-phenylenediamine, reacts with three moles... 

The salts of derivatives possessing phenyl substitutents on the selenazole ring are easily hydrolyzed in aqueous solution. 

There are very few homolytic reactions on triazolopyridines. A suggestion that the ring opening reactions of compound 1 involved free radical intermediates is not substantiated (98T9785). The involvement of radical intermediates in additions to ylides is discussed in Section IV.I. The reaction of radicals with compound 5 and its 1-substituted derivatives gives 4-substituted compounds such as 234 (96ZOK1085). A more detailed study of the reaction of the 1-methyl and 1-phenyl derivatives with r-butanol and ammonium persulfate produced 4-methyl substitution with a silver nitrate catalyst, and the side chain alcohol 235 without the catalyst (96ZOK1412). 

The thermal cyclization of m-phenylenediamine derivatives (799) by heating in diphenyl ether afforded angular l,7-phenanthroline-3,9-dicarboxylate (800), if a substituent was not present at position 2 of the phenyl ring of 799 (R = H), but the linear pyrido[3,2-g]quinolinecarbox-ylate (801, R = Me, R1 = R2 = H) was prepared from the 2-methyl-substituted derivative (799, R = Me, R1 = R2 = H) (72GEP2220294). 

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