Organic syntheses via transition metal complexes .86. Regioselective [C-3+C-2] cyclopentadiene annulation to enamines with alkynylcarbene complexes of chromium and tungsten as novel C-3 building blocks

Alkynylcarbene complexes (CO)(5)M=C(OEt)C=CPh (10) (M = Cr, W) react with tertiary 1-aminocycloalkenes CH=C(NR(2))CH2 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))CH2 (H) are formed as II 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.