Synthesis of Heterocyclic Ligands by Diheterocyclization at the Rhenium(I) Allenylidene [(triphos)(CO)₂Re{CCCPh₂}](OSO₂CF₃). 1. Reactivity with Dipolar N<i>,</i>N-Heterocycles

Abstract

1,2,3-Diheterocyclizations at the allenylidene ligand in the complex [(triphos)(CO)2Re{CCCPh2}]OTf (1; triphos = MeC(CH2PPh2)3, OTf = OSO2CF3) readily occur upon reacting 1 with N,N-heterocycles such as 1H-benzotriazole, 2-aminopyridine, and 2-aminothiazole. The reaction of 1 with 1H-benzotriazole leads to (4). Deprotonation of 4 with sodium methoxide in tetrahydrofuran at room temperature yields the alkynyl derivative (5) via ring opening of the triazaindenyl moiety in 4. Reaction of 1 with 2-aminopyridine or 2-aminothiazole in CH2Cl2 leads to the heterobicyclic compounds (6) and (8), respectively. Both complexes undergo regioselective deprotonation at the N−H heterocycle group by treatment with sodium methoxide in THF, giving the neutral species (7) and (9), respectively. The X-ray structures of the new organorhenium species 4 and 7−9 have been determined, which have confirmed that the addition of the NH bond of the N,N-heterocycle occurs always across the Cβ−Cγ double bond of the allenylidene chain.