REACTION OF AMINOCARBENE COMPLEXES OF CHROMIUM WITH ALKYNES .3. NEW INSIGHTS INTO THE MECHANISM OF FORMATION AND REARRANGEMENT OF NITROGEN YLIDES

The dissymmetrically N-substituted aminocarbene complexes (CO)(5)Cr=C(R(1))N(R(2))(R(3)) 7 (R(1) = H, R(2) = CH3, R(3) = Ph), 11 (R(1) = R(2) = CH3, R(3) = Ph), 17 (R(1) = Ph, R(2) = CH3, R(3) = cyclopropyl), 22 (R(1) = R(2) = CH3, R(3) = sec-butyl), and 24 (R(1) = Ph, R(2) = CH3, R(3) = sec-butyl) have been reacted with diphenylacetylene. Whereas complex 7 only led to the aminofuran complex 8, which could be converted to the air-stable aminofuran 9, complex 11 gave, besides the aminofuran complex 12, the pyrrolinone 13 and the imine 15 as a result of respectively the insertion of the alkyne and CO, followed by the migration of the phenyl group from nitrogen to the gamma-carbon, and the sole insertion of the alkyne followed by the migration of the phenyl group from nitrogen to the gamma-carbon. However, 17 gave an intermediate (arene)tricarbonylchromium nitrogen ylide complex (CO)(3)Cr(C29H23NO) (18). Upon heating of the sample in benzene, the cyclopropyl group, cis with respect to Cr(CO)(3) in 18, migrates from nitrogen to the gamma-carbon atom, to give a pyrrolinone Cr(CO)(3) complex 19 in which the cyclopropylgroup is trans to Cr(CO)(3). 9, 13, 15, 18, and 19 were fully characterized by X-ray diffraction studies. Crystal data for 9: C23H19ON, triclinic, space group P ($) over bar 1, a = 8.861-(1) Angstrom, b = 19.814(2) Angstrom, c = 10.817(1) Angstrom, alpha = 102.08(1)degrees, beta = 94.67(1)degrees, gamma = 105.93(1)degrees, V = 875(5) Angstrom(3), d(calc) = 1.24 g cm(-3), Z = 2. Data for 13: C24H21ON, orthorhombic, space group. P2(1)2(1)2(1), a = 9.957(6) Angstrom, b = 9.767(4) Angstrom, c = 19.244(19) Angstrom, V = 1871(2) Angstrom(3), d(calc) = 1.20 g cm(-3), Z = 4. Data for 15: C23H21N, monoclinic, space group P2(1)/c, a = 9.290(2) Angstrom, b = 22.324(3) Angstrom, c = 9.630(1) Angstrom, beta = 116.14(1)degrees, V = 1793(13) Angstrom(3), d(calc) = 1.15 g cm(-3), Z = 4. Data for 18: C29H23O4NCr, orthorhombic, space group P2(1)n, a = 12.763(11) Angstrom, b = 13.854(14> Angstrom, c = 13.577(26) Angstrom, V = 2.401(6) Angstrom(3), d(calc) = 1.39 g cm(-3), Z = 4. Data for 19: C29H23O4NCr, monoclinic, space group P2(1)/alpha, a = 4.044(5) Angstrom, b = 9.664(2) Angstrom, c = 18.035(3) Angstrom, beta = 97.93(2)degrees, V = 2424(7) Angstrom(3) d(calc) = 1.37 g cm(-3), Z = 4. A rearrangement without CO insertion could also be observed starting from complex 23a which gave 25. Finally, 24a,b led, besides to the benzannulation products 28 and 29, to the pyrrolinones 27a,b resulting from the migration of the sec-butyl group; in the case of the optically active 24b, no racemization of the migrating group is observed. The mechanisms ofthese transformations will be discussed.