Stereoselectivity in the methylenecyclopropane rearrangement and molecular distortions in methylenecyclopropane-2-carboxamide

Synthesis of Methylene- and Alkylidenecyclopropane Derivatives

“…217,218,399c,400 Recently, the X-ray crystallographic structure determination of methylenecyclopropane-2-carboxamide has shown that the molecule in its ground state exhibits significant distortion from an idealized geometry in a manner consonant with the stereochemical preferences observed in the MCP rearrangements. 409 Consistent with the above interpretation is the greatly reduced barrier to isomerization in the presence of radical-stabilizing substituents such as halogens 18a,35a,41,44b,47,49,58,59,206,208,233,410,411 or aryl groups, 51,68,74b,75 as already pointed out. This makes the rearrangement synthetically useful for the obtainment of the thermodynamically more stable ACP derivatives.…”

Cumulated Trienephosphine Oxides. Bimolecular Trapping of an Alkylidenecyclopropylidene

“…The changes in molecular geometry, and hence bond energies, must exert a strong influence on the chemical behavior of the 1-alkylidene-2-bromo-2-lithiocyclopropanes or alkylidenecyclopropylidenes. In those reactions in which ring opening takes place, it is the C(1)−C(2) bond that should be broken preferentially and not the C(1)−C(3) bond 4 2 Optimized Energies and Bond Lengths and Angles a of Carbenoids 24a, 24b, and 11α Calculated Using the ab Initio Mp2/Sto-3G b and Comparison of Geometrical Data with 22 and 23 c 24a 24b 11α 22 d 23 e 24a 24b 11α 22 23 energy (au) −2704.1079 −2782.25538 −3686.4349angles LUMO (eV) 2.798 2.888 2.774C(1)−C(2)−C(3) 58.8 59.0 59.2 58.1 57.7 HOMO (eV) −6.695 −6.511 −5.612C(2)−C(1)−C(3) 58.558.258.358.8 net chargesC(1)−C(3)−C(2)62.762.862.563.563.6 C(1)−0.1570.0020.004Li−C(2)−C(1)149.8149.8150.0 C(2)−0.039−0.048−0.050Li−C(2)−C(3)150.7150.1149.6 C(3)−0.022−0.029−0.042α175.3174.0173.8 C(4)−0.139−0.143−0.151Br−C(2)−C(1)113.0115.8115.9 Br−0.009−0.005−0.007Br−C(2)−C(3)112.5113.7113.8 Li0.0950.0800.086β116.4118.8118.9 P0.883…”

Structure of methylenecyclopropane-2-carboxamide by time-of-flight neutron diffraction

“…The initial coordinates for the non-hydrogen atoms were those from the X-ray structure (Van Derveer, Baldwin & Parker, 1987). Hydrogen atoms were located in a difference Fourier map using phases calculated from the non-hydrogen atomic coordinates.…”

“…The atomic positional and equivalent isotropic thermal parameters are given in Table 1 interactions. Cooling from room temperature (Van Derveer, Baldwin & Parker, 1987) to 20 K produces a 7.3% reduction of the unit-cell volume due to contraction of a, b and c by 3.2, 2.8 and 1.1%, respectively. The atom-labeling scheme is shown in Fig.…”

“…3. Based on preliminary analyses, it was previously reported (Van Derveer, Baldwin & Parker, 1987) that the H(4)--C(4)--H(5) plane is also slightly twisted about the C(1)--C(4) vector such that one of the diastereotopic faces of the C(4) methylene group appears to be oriented more favorably for bonding to C(2). The results of the current analysis are that the H (4) …”