Duraiswamy A. Jeyaraj

The directional changes in torsion angles alone after complexation of the carbonyl oxygen with a prototypical cation such as H+ predict the facial selectivity of substituted cyclohexanones. An ab initio investigation

Abstract H + was taken as a prototypical cation for complexation with the carbonyl oxygen of 3-oxa-, 3,5-dioxa-, and 3-thiacyclohexanones. The geometries of the complexes were fully optimized using ab initio MO calculations with 6-31G basis set. The complexation desymmetrizes the molecular geometry further to an extent that the torsion angle changes on the axial face can be rationally used for the prediction of the facial selectivity in reactions with nucleophiles. The torsion angle changes are sensitive to the nature, position, and orientation of the substitutents. Based on the theory of stereoelectronic control and corroborated by ab initio MO calculations, a simple approach to the prediction of facial control in reactions of selected substituted cyclohexanones with nucleophiles is described. Some evidence is also presented against the known transition state models.

The Cation Complexation Model Predicts the Experimental π-Facial Selectivity of 2-ax- and 2-eq-Substituted Cyclohexanones. A Detailed Ab Initio MO Investigation

Abstract The geometrical changes on complexation of the carbonyl oxygen with prototypical cations such as H + and Li + are in tune with the polarity features of the C–X bonds in 2-ax-X-cyclohexanones (X=Cl, F, SR, OR; R=H, Me); the stereoelectronic effects apply. While the 2-ax-Cl- and 2-ax-SR-cyclohexanones are predicted to favor axial attacks, the 2-ax-OR- and 2-ax-F-cyclohexanones must capture a nucleophile predominantly from the eq-direction. The eq-selectivity of 2-ax-OR-cyclohexanone is in contradiction with the torsional model of Anh and Felkin. The Houk model will also fail due to the eminent steric interactions arising from the 2-ax-OMe function in the eq-TS. Neither the Anh–Felkin model nor the Cieplak model could be applied to 2-eq-MeO-cyclohexanone. The complexation model, however, predicts eq-selectivity in full agreement with experimental results. Second order perturbation theory analysis of the Fock matrix in NBO basis indicates that the role of the antiperiplanar effects is not as significant as perceived earlier by Cieplak and by Anh and Felkin.

Diastereofacial selectivities of substituted 5-aza-and 5-bora-2-adamantanones. Application of the complexation model and its ab initio MO investigation

N-Substituted 5-aza-2-adamantanones and 5-bora-2-adamantanone have been studied by ab initio MO methods at Becke3LYP level for their diastereofacial selectivities in reactions with nucleophiles by applying the complexation model. The facial predictions are fully consistent with the experiments. This is to be emphasized that in a given substrate there may be centres other than the carbonyl oxygen that may compete for the cation and, thus, contribute to the overall diastereodetermination. Other models such as the Cieplak model. Anh-Felkin model, and Houk model may or may not apply.

3-Halocyclohexanones. Torsion angle changes after cation-carbonyl complexation dictate the facial selectivity in reactions with nucleophiles: An ab initio investigation

Abstract The geometrical changes that take place after complexation of the carbonyl oxygen of 3-halocyclohexanones with prototypical cations such as H + and Li + were calculated using ab initio MO methods at 6-31G level. The torsion angle changes interpret rationally the experimentally known axial preference of the 3-eq-derivatives and the axial preference (predicted from transition state calculations) of the 3-ax-species. Stereoelectronic effects in 3-ax-halocyclohexanones and 1,3-dipolar interactions in 3-eq-halocyclohexanones after complexation of the carbonyl oxygen with cations such as H + and Li + account for the experimentally observed and the predicted diastereoselectivities, respectively, of these molecules. The complexation induces pyramidalization of the carbonyl carbon and controls the p orbial to adopt an energetically favorable orientation (ax or eq) for capture by a nucleophile.

2-(7-Ethylidene-6-methyl-1-oxa-4-thiaspiro-[4.5]dec-7-yl)ethanol

The crystal of the title compound, C13H22O2S, has two independent molecules in the asymmetric unit. The molecular dimensions are normal. Molecules are linked into chains along the b direction by O—H⋯O hydrogen-bonds, with O⋯O 2.655 (5) and 2.693 (5) A.

Oxa-thia-spiro-decene Derivatives

The crystal structures of (5R)-(10-methyl-1-oxa-4-thiaspiro[4.5]dec-9-en-9-yl)phenyl(S)-methanol, C 16 H 20 O 2 S, (1), and 1(S)-[(5R)-10-methyl-1-oxa-4-thiaspiro[4.5]dec-9-en-9-yl)ethyl 4-methoxybenzoate, C 19 H 24 O 4 S, (2), are composed of independent molecules separated by normal van der Waals distances. The molecular dimensions in both structures are normal. The hydroxyl and heterocyclic ring O atoms exhibit a short intermolecular hydrogen bond of the order of 2.814 (4) A in (1) forming a chain of molecules along the c axis.