No abstract

5-Diazomethyl-l,4-diphenyl-l,2,3-triazole (I) reacts with monosubstituted benzenes at 40-50°to give 72-90% yields of mixtures of 7-(l,4-diphenyltriazol-5-yl)tropilidenes in which the predominant isomer has the substituent in the 3 position (CH3 or F) or the 2 position (CH3O). The relative reactivities of monosubstituted benzenes toward the carbene from I were determined by competition experiments; they could be correlated by a Hammett equation in ap with = -1.0, corresponding to an electrophilic species with a selectivity more closely resembling that of carboethoxynitrene than carboethoxycarbene. 5-(a-Diazobenzyl)-l,4-diphenyltriazole thermolyzed more slowly than the diazomethyl analog, but still showed first-order kinetics with a rate constant independent of solvent in the absence of a proton source. It did not form addition or insertion products, but gave a mixture consisting principally of the symmetrical tetrasubstituted ethylene, the corresponding ethane, and 5benzoyl-1,4-diphenyltriazole. These products, the result of dimerization, abstraction of hydrogen, and reaction with O2, imply the intermediacy of a carbene in the triplet state.

An improved synthesis of 5-(diazomethyl)-1,4-diphenyl-1,2,3-triazole (1) has been developed. It fragments to a carbene at 40-50 °C and reacts with o-, m-, or p-xylene or indan at 40-50 °C to give high yields of cycloheptatriene products, presumably through an initial norcaradiene adduct. In each case only one major isomer was obtained, indicating that steric interactions are a more important influence on the site selectivity of carbene attack than is the electronic directing influence of the alkyl groups. Low-temperature nuclear magnetic resonance spectroscopy found no evidence of dynamic equilibrium between the cycloheptatriene and detectable amounts of the norcaradiene isomers down to -100 °C. With mesitylene, 1 reacted to give an 80% yield of 1,3,5-trimethyl-7-(1,4-diphenyl-1,2,3-triazol-5-yl)norcaradiene ( 8), the 13C NMR spectrum of which indicates a dynamic equilibrium with the cycloheptatriene valence tautomer 9. The initial adducts, isolable in their pure state, rearranged on mild heating to isomeric cydoheptatrienes having a structure conjugated with the diphenyltriazolyl substituent.The kinetics were first-order with Et = 26.9 or 27.9 and 24.8 kcal/mol for the p-and m-xylene and mesitylene adducts, respectively. The kinetic parameters and the NMR spectra of the initial adducts and their rearranged isomers are interpretable in terms of the large steric interactions between the diphenyltriazolyl group and the substituents on the cycloheptatriene ring and interference with rotation of the diphenyltriazolyl group but not with conformational inversion. In the rearrangement of 8/9 derived from 2,4,6-trideuteriomesitylene, there was no kinetic isotope effect.The most general entrance into the norcaradiene-cycloheptatriene system (commonly called tropilidene) is by addition of carbenes to benzene and its derivatives. Although addition of carbenes to aromatic rings was first reported by Büchner and Curtius in 18852 and its synthetic

Melting points were taken on a Thomas-Hoover apparatus and are uncorrected. Infrared spectra were recorded with a Perkin-Elmer 2376 spectrophotometer; NMR spectra were obtained with a Varian A-60D or a T60 spectrometer using Me& as an internal standard (6 0); mass spectra were obtained with a Hltachi RMV-7 spectrometer. Gas chromatography was done with either an F & M Biomedical Gas Chromatograph Model 400 or Model 402; elemental analyses were performed T h e synthesis of a tetracyclic analogue (2) of t h e heteroyohimbine alkaloid ajmalicine (1) is described. T h e synthesis makes use of a novel alternative t o t h e K o r t e reaction for the preparation of t h e dihydropyran ester portion (1 1) of the molecule.

Als Voruntersuchungen für eine Synthese von Ajmalicin (I) wird die Herstellung der ähnlichen Verbindung (II) , ausgehend von (III),beschrieben.