5-Diazomethyl-4-methoxycarb9nyltriazoles are capable of undergoing ring-degenerate rearrangements (19 + 0) when a strong electron-withdrawing substituent (e.g. pnitrophenyl or o.p-d%nitrophenyl) is located at the N-l position. Whereas the unrearranged diaeomethyltrlazole 198 decomposes thermally in benzene to give the cycloheptatriene 2&, the rearranged diaso conpound 20b yields the norcaradiene 22b. Several methods are described for prepar= the aldehydes 1 which arethe precursors of the diaeomethyltrfaroles.
Molecular rearrangements of five-membered heterocycles which furnish the same ring system, are denoted as ring-degenerate rearrangements. 1 A typical example is the interconversion of l-aryl-5-amino-1,2,3-triazoles (I, R5 = NH21 and 5-anilino-1,2,3triazoles (z), known as the Dinuoth rearrangement. 1 This reaction involves the exchange of an endocyclic with an adjacent exocyclic nitrogen atom via a diazoimine (2) as intermediate (Scheme I). Ring-degenerate rearrangements of triazoles may also occur with the participation of two side-chain atoms if the RI-substituent is an imine function. Thus, Becher et al. 2 reported the thermal isomerization of 4-iminomethylene-5-hydroxy-1,2,3-triaxoles (1, R4 = CH=NR, R5 = OH) into triazole-4-carboxamides (4). We now describe a third case of ring-degenerate rearrangement of triazoles where three side-chain atoms are incorporated into the newly formed triazole. As shown in Scheme I, this is possible by introducing a diazomethyl function at the S-position (1+2 +s,. --Smith et a1.3 have already investigated the chemistry of 5-diaxomethyl-1,4-diphenyltriazole 2 but did not observe any rearrangement. Indeed, in benzene at 50ยฐ, the diazo function decomposes, and the resulting carbene adds to the solvent.with formation of the cycloheptatriene 1. Thus, decomposition of the diazo function occurs more rapidly than ring-opening of the triazole.
In order to stabilize the diazo substituent and to facilitate triazole cleavage, we have placed an ester function at the 4-position of A. Also, the R1-substituent was varied from phenyl to nitro-substituted phenyls. These groups are known to promote the Dimroth rearrangement of 5-aminotriaxoles 4 and were expected to have a similar effect on our compounds.
RESULTS AND DISCUSSION
Since the 5-formyltriazoles 11 are the key intermediates in the synthesis of the diazo compounds 19, several approaches have been devised to prepare them. For instance, the 1,3-dipolar cycloaddition of methyl 4-hydroxy-2-butynoate (8)' with