作者:Stefan E. Boiadjiev、David A. Lightner
DOI:10.1016/s0957-4166(02)00481-0
日期:2002.8
As observed by NMR, iodopyrroles 1a and 1b (ethyl and methyl 3,5-dimethyl-4-[(1'-iodo-2',2'-dimethyl)propyl]pyrrole-2-carboxylate) and a variety of related derivatives with iodine replaced by methoxy 2, thiomethyl 3, acetic acid esters 4, propionic acid ester 5 or malonic esters 6 exhibit restricted rotation about the C(4)-C(1') bond due to the bulky tert-butyl group and an ortho effect from the sterically crowded 3,5-dimethylpyrrole. Most of the compounds, which are members of the rare class of atropisomers due to restricted rotation about an sp(3)-sp(2) C-C bond, undergo diastereomeric enrichment by preparative TLC and crystallization. From dynamic NMR studies of the enriched diastercomers one can determine kinetic and thermodynamic parameters associated with the atropisomerism, e.g., DeltaG(double dagger) similar to24 kcal/mol for 1 and 5 (313 K), similar to22 kcal/mol for 3 (273 K), and similar to25 kcal/mol for 6 (313 K) in C2D2Cl4 solvent. (C) 2002 Elsevier Science Ltd. All rights reserved.