Probing the Structural and Electronic Effects on the Origin of ?-Facial Stereoselectivity in 1-Methylphosphole 1-Oxide Cycloadditions and Cyclodimerization.

ABSTRACT: We have examined the ?-facial stereoselectivity in the Diels-Alder reactions of phosphole oxides computationally. The experimentally observed syn-cycloadditions have been rationalized with the Cieplak model and distortion-interaction model. The natural bond orbital analysis suggests that the hyperconjugative interactions are energetically preferred between the antiperiplanar methyl group present in the -P=O unit and the developing incipient (-C-C-) bond in syn-adducts in accordance with the Cieplak model. The distortion-interaction analysis carried out for syn and anti transition states of Diels-Alder reactions of 1-substituted phosphole 1-oxide with different dienophiles reveals that the syn selectivity is favored by distortions and interaction energies compared with the anti selectivity. The formation of a syn adduct is also stabilized by the ?_CC-?*_PO orbital interaction, and the repulsive n-? interaction destabilizes the anti adduct that leads to the 7.0 kcal/mol thermodynamic preference for the former adduct. Furthermore, the distortion-interaction model rationalizes the formation of stereospecific products in these Diels-Alder reactions, which however is not explicable with the much-debated Cieplak model.

SUBMITTER: Bhai S 

PROVIDER: S-EPMC6645475 | biostudies-literature | 2018 Sep

REPOSITORIES: biostudies-literature