Photochemistry of 1-allyl-4-aryltetrazolones in solution; structural effects on photoproduct selectivity

Abstract

The photochemistry of tetrazolones derived from the carbocyclic allylic alcohols cyclohex-2-enol and 3-methylcyclohex-2-enol and from the natural terpene alcohol nerol was investigated in solution with the aim of assessing the effect of solvent and of structural constraints imposed by bulky allylic moieties on photoproduct selectivity and stability. Photolysis of tetrazolones derived from nerol and cyclohex-2-enol afforded the corresponding pyrimidinones as major products through a pathway that appears to be similar to that proposed for other 1-allyl-4-phenyl-1,4-dihydro-5H-tetrazol-5-ones derived from acyclic and unhindered allylic alcohols previously investigated but photolysis of the tetrazolone derived from the bulkier 3-methylcyclohex-2-enol 4c leads to formation of a benzimidazolone, indicating that, in this case, cyclization of the biradical formed upon extrusion of N 2 involves the phenyl substituent and not the allylic moiety. Theoretical calculations (DFT(B3LYP)/3-21G*) were conducted to support the interpretation of the experimental results and mechanistic proposals. Laser flash photolysis experiments were conducted with the aim of clarifying the nature of the intermediate involved in the primary photocleavage process.

Substituent Effects on EI-MS Fragmentation Patterns of 5-Allyloxy-1-aryl-tetrazoles and 4-Allyl-1-aryl-tetrazole-5-ones; Correlation with UV-Induced Fragmentation Channels

“…All of the compounds investigated in this work were synthesized in our laboratory following the approach depicted in Scheme 1, developed previously [31,32,43,44]. All the compounds studied were characterised and described elsewhere [30,[43][44][45]. The mass spectra of the studied tetrazoles were obtained on a VG 7070E mass spectrometer by electron ionization (EI) at 70 eV and are presented as supplementary material.…”

“…The results gathered from mass spectra analysis provide accurate identification of the species formed upon labile bond cleavage of the studied tetrazoles when ionised through electronic impact, as well as the assessment of divergent cleavage patterns in the function of the diversified nature of the substituents. Furthermore, the results gathered using the EI-MS technique are compared with those obtained from UV-induced photolysis of monomeric tetrazoles isolated in cryogenic matrices of noble gases [ 12 , 30 ] to further assess the degree of comparability between the fragmentation patterns obtained using the two forms of excitation, as this analysis can provide a useful complementary technique in reactivity studies of this class of molecules and possibly others.…”

Genesis of rare molecules using light-induced reactions of matrix-isolated tetrazoles

“…The relevance of allyltetrazole derivatives in organic synthesis attaches ever increasing interest to their study. Particularly, the title compound of this subsection is an important precursor of other biologically active heterocycles, through photolysis [60,61], and may be obtained from the corresponding 5-allyloxytetrazoles in quantitative yields through a thermally induced Claisen-type isomerization [62][63][64][65][66]. Furthermore, allyltetrazolones are important structural units of biologically active systems, acting as key intermediates in the biosynthesis of several important biomolecules [67][68][69].…”

Photochemistry of 1-Phenyl-4-Allyl-Tetrazol-5-One: A Theoretical Study Contribution towards Mechanism Elucidation

“…In chemical synthesis, they are widely used in the preparation of heterocyclic compounds with nitrogen atoms. Synthetic routes are described for various classes of compounds [12], using tetrazoles or derivatives, such as 9H-pyrimido(4,5-b)indoles [13], diaziridinones [14], iminoaziridines [15], carbodiimides [16], oxazines [17], benzimidazolones [16], and pyrimidinones [18][19][20].…”

“…The matrix isolation approach limits the study to confined processes, eliminating alternative reaction pathways that could arise through molecular diffusion (except for small species produced), or that depend on conformational rearrangements [18,22,23,26]. Solution photoreactions have more associated variables, since it is known that the solvent and other reaction conditions have a direct influence on the yield and selectivity of the photodegradation of tetrazolic compounds [12].…”