Vergleich 1- und 2-substituierter 5-(Diazomethyl)tetrazole

Buchner Reaction/Azirine Modification Approach Toward Cycloheptatriene Containing Nitrogen Heterocyclic Scaffolds

The reaction conditions for the Buchner reaction of 2-(diazoacetyl)-2H-azirines with benzene leading to 2-(cyclohepta-2,4,6-trien-1-yl)-2H-azirines have been found. The azirine fragment of these compounds was subsequently used to prepare 5-(cyclohepta-2,4,6-trien-1-yl)isoxazoles and α-(cyclohepta-2,4,6-triene-1-ylcarbonyl)-1H-pyrroles. NMR and DFT calculations showed that the cycloheptatriene-norcaradiene valence isomerization in the corresponding moieties of synthesized azirines, isoxazoles, and pyrroles is very fast at room temperature. Cycloheptatriene valence isomer predominates in azirines and pyrroles, while 5-(cycloheptatrienyl)isoxazoles exist in a pure cycloheptatriene form at 25 °C in chloroform solution. In accordance with the X-ray analysis, two of the synthesized pyrroles crystallized as norcaradiene isomers from a solution of equilibrium mixture of valence isomers. Reductive isoxazole ring opening using the Mo(CO)₆/H₂O reductive system afforded (Z)-3-amino-3-aryl-1-(cyclohepta-2,4,6-trien-1-yl)prop-2-en-1-ones, which are pure cycloheptatriene isomers. α-(Cycloheptatrieneylcarbonyl)-1H-pyrroles were transformed into the α-(benzylcarbonyl)-1H-pyrroles under cooperative TFA/Rh₂(TFA)₄ catalysis.

The Zwitterionic Structure of the Parent Amidinium Tetrazolide and a Rare Tetrazole Ring-Opening Reaction

A crystallization method for 5-amidinium tetrazolide (1) was developed. Crystals of the pure zwitterion 1 enabled the unambiguous assignment of the structure as an inner-salt rather than the amidine tetrazole postulated previously. The solid-state structure of 1 consists of two sets of hydrogen bonds that form a tightly networked two-dimensional sheet. The reaction of amidinium tetrazolide 1 with SOCl2 in the presence of 2.0 equiv. of Et3N produces 3-amino-4-azido-1,2,5-thiadiazole (2) as the sole product. The required tetrazole ring-opening reactivity suggests that the tetrazole moiety may function as a masked geminal azido-nitrene. The thionyl chloride reaction with the amidinium zwitterion 1 occurs not exclusively at the amidine, but rather in the Bay-region of 1, which comprises both the amidinium group and tetrazolide ring. Thiadiazole 2 has a planar structure with a 2D network of hydrogen bonds between the amino group and nitrogen atoms and an S⋯N interaction between the azido group and sulfur.