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The barrier to rotation around the N-alkenyl bond of 38 N-alkenyl-N-alkylacetamide derivatives was measured (ΔG⧧ rotation varied between 20 kcal mol–1) were studied to determine the regiochemistry of cyclization. Those with high barriers (>27 kcal mol–1) did not lead to cyclization, but those with lower values produced highly functionalized γ-lactams via a 5-endo-trig radical–polar crossover process that was terminated by reduction, an unusual cyclopropanation sequence, or trapping with H2O, depending upon the reaction conditions. Because elevated temperatures were necessary for cyclization, this precluded study of the asymmetric transfer in the reaction of individual atropisomers. However, enantiomerically enriched atropsiomeric enamides should be regarded as potential asymmetric building blocks for reactions that can be accomplished at room temperature.\ud \ud

Thirty-four @2-R1C2R2)Co2(C0)6 complexes (14 new) were prepared and characterized by their IR v(C0) and lH- and 13C-NMR spectra. The 13C-NMR chemical shifts of the coordinated sp carbon atoms were correlated with those of the corresponding free acetylenes. This indicated that the interaction between the R1 and R2 groups and the c2co2(co)6 moiety is very sensitive not only to the donor/acceptor character of R1 and R2 but also to the orbital symmetry of the atoms attached directly to the C(sp) atoms. The changes of the W3C) values of the C(sp) atoms upon coordination were also analyzed in these terms. It is concluded that although the dinuclear p2-coordination of the acetylene results in a high degree of excitation the stability of the c2co2(co)6 moiety diminished the reactivity of the organic ligand. Differences in the reactivity of the @2-R1C2R2)Co2(CO)6 complexes in carbonylation are also discussed. The crystal and molecular structure of (PhC2SiPhs)Coz(CO)a was determined by single crystal X-ray diffraction. This compound crystallizes in the orthorhombic Pbca space group with a = 28.790(2) A, b = 11.577(1) A, c = 17.833(2) A, 2 = 8. The structure was determined with R = 0.039, R, = 0.036.