A Brave New World: The Heteroatom Chemistry of 1,3,2,4‐Benzodithiadiazines and Related Compounds

Abstract

This review highlights the most important advances in the heteroatom chemistry of 1,3,2,4-benzodithiadiazines (π-excessive and formally antiaromatic heterocycles), covering methods for synthesis, nontrivial features of the molecular and π-electronic structure, spectral properties, and reactivity, in particular the transformations into persistent π-radicals.

Interaction of 1,3,2,4‐Benzodithiadiazines with Aromatic Phosphines and Phosphites

“…Reactions required higher temperatures but even at 20°C P(OPh) 3 interacted with both hydrocarbon 1b and fluorocarbon 1c derivatives very slowly to give after several days complex reaction mixtures in which only XP(OPh) 3 (X = S, O, in proportion 1:1 and 1:2.3, respectively) were identified by 13 С and 31 Р NMR and GC‐MS techniques (Scheme ). In the case of X = S, initial compounds 1 were obviously the source of sulfur (desulfurization of sulfur–nitrogen rings, cages, and chains by PR 3 compounds is well known [c]), whereas with X = O a source of oxygen is not entirely clear. The experiments were performed under argon, but their duration was 12–15 days; and atmospheric oxygen might enter the reaction systems to oxidize P(OPh) 3 into OP(OPh) 3 .…”

“…1,3,2,4‐Benzodithiadiazines ( 1 , Chart ) represent a relatively rare class of compounds possessing formal features of antiaromaticity in combination with moderate thermal stability. Their heteroatom reactivity is of obvious fundamental interest . Particularly, it was found that 1,3,2,4‐benzodithiadiazine and its derivatives, including low‐ and high‐fluorinated ones (as well as 1‐Se congener of trifluoro derivative) react with PPh 3 (Ph = C 6 H 5 ) to give chiral 1,2,3‐benzodithiazol‐2‐yl iminophosphoranes ( 2 , Chart ) inaccessible by other approaches including classical Kirsanov and Staudinger reactions .…”

“…The exact mechanism of this seemingly soft‐El–soft‐Nu orbitally controlled reaction is unclear. Formally, 1,3,2,4‐benzodithiadiazines act in this reaction as they are isomeric singlet nitrenes (observed in a cryogenic matrix as a product of their photochemical rearrangement ), which iminate oxidatively the P atom of the phosphine. In the crystalline state, compounds 2 reveal interesting structural feature as one of Ph groups and the hetero ring are always face‐to‐face oriented (π‐stacked) with interplanar separation being shortened as compared with the sum of corresponding van der Waals radii .…”

Redox properties and radical anions of fluorinated 2,1,3‐benzothia(selena)diazoles and related compounds

“…The DFT approach at the (U)B3LYP/6‐31+G(d)39, 40 level of theory was used for the calculations since it performs well for molecular structures and properties of main‐group compounds including electron affinities and hyperfine coupling constants 20, 41, 42. Previously, the (U)B3LYP method was successfully employed to reproduce the properties of a series of both closed‐ and open‐shell chalcogen–nitrogen cycles and cages including RAs 25–31, 43–50. Quantum chemical calculations on RAs and their neutral precursors were carried out with full geometry optimization using the GAMESS51 and GAUSSIAN‐0352 programs.…”

Synthesis and Applications of 5‐Membered Chalcogen‐Nitrogen π‐Heterocycles with Three Heteroatoms

“…It was first observed with thermolysis of 1,3,2,4‐benzodithiadiazines (Scheme ) within the study of the reactivity of those 12π‐electron, i. e . formally antiaromatic, heterocycles . Then it was found that synthetically it is much more convenient to generate the radicals by reduction of 1,2,3‐dithiazoliums under conditions favorable for the radicals self‐condensation .…”