Organic Syntheses via Transition Metal Complexes. 86. Regioselective [C3 + C2] Cyclopentadiene Annulation to Enamines with Alkynylcarbene Complexes of Chromium and Tungsten as Novel C3 Building Blocks

Alkynylcarbene complexes (CO) 5 M C(OEt)C⋮CPh ( 10 ) (M = Cr, W) react with tertiary 1-aminocycloalkenes CH C(NR 2 )CH 2 17 − 23 (cyclopentenes, -hexenes, and -heptenes, dihydronaphthalenes and -phenanthrenes; NR 2 = NMe 2, pyrrolidino, and morpholino) to afford cyclopentadiene annulation products 24 − 30 in an overall [3 + 2] cycloaddition process. The reaction is highly regioselective and proceeds under very mild conditions in 60−99% yields. 1-Metalla-1,3,6-heptatrienes (CO) 5 M C(OEt)CH C(Ph)−CHC(NR 2 ) CH ( G) and 1-metalla-1,3,5-hexatrienes (CO) 5 M C(OEt)CH C(Ph)−C C(NR 2 )CH 2 ( H) are formed as key intermediates. Compounds H cyclize to give cyclopentadiene complexes as precursors to the cyclopentadienes 24 − 30 . Hydrolysis of 1-metalla-1,3,6-heptatrienes G leads to the production of pyran-2-ylidene complexes, e.g., 32a, b .