Hetero Diels–Alder Reactions of Masked Dienes Containing Heavy Group 15 Elements

Treatment of N , C , N ‐chelated organopnictogen(I) compounds ArE ( 1 – 3 ) (Ar=2,6‐(RN=CH) 2 C 6 H 3 , E/R=As/Dmp ( 1 ), Sb/ t Bu ( 2 ), and Bi/ t Bu ( 3 ), where Dmp=2,6‐Me 2 C 6 H 3 ) with various electron‐deficient alkynes RC≡CR′ (R/R′=CO 2 Me (DMAD), R/R′=H/CO 2 Me, or R/R′=NC 5 F 4 ) 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(CO 2 Me) 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.