Treatment of N,C,N-chelated organopnictogen(I) compounds ArE (1–3) (Ar=2,6-(RN=CH)2C6H3, E/R=As/Dmp (1), Sb/tBu (2), and Bi/tBu (3), where Dmp=2,6-Me2C6H3) with various electron-deficient alkynes RC≡CR′ (R/R′=CO2Me (DMAD), R/R′=H/CO2Me, or R/R′=NC5F4) affords different types of heterocyclic compounds. In these reactions, 1–3 act as hidden dienes and participate in hetero-Diels–Alder (DA) reactions, a feature that has been only rarely reported for heavier pnictogen compounds. In this way, reactions of 1 furnished the set of 1-arsanaphthalenes 4–6. The most likely mechanism involves two steps, that is, an arsa-DA reaction giving a 1-arsa-1,4-dihydro-iminonaphthalene, followed by CH→NH proton migration. In contrast, this reaction sequence terminates at the first step in the case of the antimony analogue 2, thus giving the 1-stiba-1,4-dihydro-iminonaphthalenes 7 and 8. Reactions of the bismuth congener 3 gave one of two products depending on the alkyne used. Reaction of 3 with DMAD gave 1-bisma-1,4-dihydro-iminonaphthalene 9, whilst its reaction with two equivalents of HC≡C(CO2Me) gave bismacyclohexadiene (10). All compounds have been characterized by NMR, IR, and Raman spectroscopies and X-ray diffraction analysis. The experimental data were complemented by a computational study, including a description of the reaction profiles of the hetero-DA reactions and an assessment of the aromaticities of the heterocyclic naphthalene derivatives.
Bibliographical noteFunding Information:
The authors (L.D.) thank the Czech Science Foundation (no. 18-10222S). J.T. would like to acknowledge the financial support of the Research Foundation Flanders (FWO; Project No. 12Y7718N) and the computational resources and services provided by the Shared ICT Services Centre funded by the Vrije Universiteit Brussel, the Flemish Supercomputer Centre (VSC), and the FWO. The authors would also like to thank Tatiana Woller for her generous help with the ESI-3D program.
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