title: A Nonempirical Approach for Direct Determination of the Absolute Configuration of 1,2-Diols and Amino Alcohols Using Mg(II)bisporphyrin.
abstract: We report here a simple, facile, and direct nonempirical protocol for determining the absolute stereochemistry of a variety of chiral 1,2-diols and amino alcohols at room temperature with no chemical derivatization using Mg(II)bisporphyrin as a host. Addition of excess substrates resulted in the formation of a 1:2 host-guest complex in which two substrates bind in an unusual endo-endo fashion because of interligand H-bonding within the bisporphyrin cavity leading to the formation of a unidirectional screw in the bisporphyrin moiety that allowed us an accurate absolute stereochemical determination of the chiral substrate via exciton-coupled circular dichroism (ECCD). The sign of the CD couplet has also been found to be inverted when the stereogenic center is moved by one C atom simply from the bound to an unbound functionality and thus able to discriminate between them successfully. Strong complexation of the alcoholic oxygen with Mg(II)bisporphyrin rigidifies the host-guest complex, which eventually enhances its ability to stereochemically differentiate the asymmetric center. The ECCD sign of a large number of substrates has followed consistent and predictable trends; thus, the system is widely applicable. Moreover, computational calculations clearly support the experimental observations along with the absolute stereochemistry of the chiral substrate.
authors.affiliation: Department of Chemistry, Indian Institute of Technology Kanpur , Kanpur 208016, India.
authors.forename: Sk Asif
authors.initials: SA
authors.lastname: Ikbal
authors.affiliation: Department of Chemistry, Indian Institute of Technology Kanpur , Kanpur 208016, India.
authors.forename: Avinash
authors.initials: A
authors.lastname: Dhamija
authors.affiliation: Department of Chemistry, Indian Institute of Technology Kanpur , Kanpur 208016, India.
authors.forename: Sanfaori
authors.initials: S
authors.lastname: Brahma
authors.affiliation: Department of Chemistry, Indian Institute of Technology Kanpur , Kanpur 208016, India.
authors.forename: Sankar Prasad
authors.initials: SP
authors.lastname: Rath