Structure and Photochemistry of a Saccharyl Thiotetrazole

The molecular structure
and photochemistry of 5-thiosaccharyl-1-methyltetrazole
(TSMT) were studied by means of matrix-isolation FTIR spectroscopy,
X-ray crystallography, and theoretical calculations. The calculations
predicted two conformers of TSMT that differ in energy by more than
15 kJ mol–1. The infrared spectrum of TSMT isolated
in solid argon was fully assigned on the basis of the spectrum calculated
(O3LYP/6-311++G­(3df,3pd)) for the most stable conformer. In the crystal,
TSMT molecules were found to assume the same conformation as for the
isolated molecule, with each molecule forming four hydrogen bonds
with three neighboring molecules, leading to a network of TSMT oligomers.
Upon UV (λ = 265 nm) irradiation of the matrix-isolated TSMT,
two photodegradation pathways were observed, both arising from cleavage
of the tetrazolyl ring. Pathway a involves cleavage
of the N1–N2 and N3–N4 bonds with extrusion of N2, leading to photostable
diazirine and thiocarbodiimide derivatives. The photostability of
the photoproduced diazirine under the conditions used precluded its
rearrangement to the nitrile imine, as reported for 5-phenyltetrazole
by Bégué et al. (J. Am. Chem. Soc. 2012, 134, 5339). Pathway b involves
cleavage of the C5–N1 and N4–N3 bonds, leading to a thiocyanate and methyl
azide, the latter undergoing subsequent fragmentation to give CNH.