Organic syntheses via transition metal complexes. 75. Phosphinonaphthalenes and phosphinoindenes by cyclization of alkynyl carbene complexes (M = Cr, W)

Article abstract of DOI:10.1021/om00001a035

1-Amino-2-ethoxy-4-phosphinonaphthalenes 6a,b (>90% yields) are obtained from (phenylalkynyl)carbene complexes (CO)₅M=C(OEt)-C≡C-Ph (M = Cr, W) 1 by a novel two-step carbene/alkyne benzannulation. The first step involves the formation of (E)-(2-phenyl-2-phosphinoethenyl)carbene complexes (CO)₅M=C(OEt)-CH=C(Ph)-PR₂ (E)-3a-c by 3-addition of secondary phosphines HPR₂ (R = t-Bu, c-C₆H₁₁) 2a,b to 1. A subsequent addition of isocyanides R¹NC (R = t-Bu, c-C₆H₁₁) 4a,b to (E)-3a-c yields ketene imine complexes (CO)₅M[R¹N=C=C(OEt)-CH=C(Ph)-PR₂] A by the insertion of 4 into the M=C bond of 3. (Metal-free) ketene imines are generated from A by ligand displacement with 4 and cyclize spontaneously to 6. Thermolysis of (E)-3a-c affords (CO)₅M phosphinoindene complexes 9 and 10. Reaction of 9 or 10 with pyridine yields phosphinoindenes 12 and pyridine complexes (CO)₅M(C₅H₅N) 11. 10a, C₂₄H₂₉CrO₆P, was characterized by X-ray diffraction. It crystallizes in space group P1 No. 2 with cell parameters a = 9.412(1) ?, b = 11.455(2) ?, c = 11.962(2) ?, = 89.10(1)°, β = 79.09(1)°, γ = 88.60(1)°, Z = 2, R₁ = 0.063, and wR² = 0.117.