Kinetic Enzymatic Resolution of Cyclopropane Derivatives

Abstract

The kinetic enzymatic resolution of cyclopropane acetates was systematically investigated utilizing 16 different hydrolases. Best results were obtained with hydrolyses in the presence of Candida antarctica B lipase.

Cycloadditions of Alkenylboronic Derivatives

“…Again, research in this field was pioneered by Pietruszka and coworkers; they studied cyclopropanation of chiral 1,3-dioxolane-derived alkenyl boronates 35-38 (Table 2). 38,40 A general trend which follows from Table 1 is that cyclopropanation with diazomethane-palladium(II) acetate (Method A) typically gave the target products 39 and 40 in higher yields (88-95%) as compared to the Simmons-Smith reaction (Method B) (58-72%). Nevertheless, the diastereoselectivity was auxiliary-controlled (and hence modest for non-chiral auxiliaries) for the Method A, and side-chain-controlled for the Method B. Matched/mismatched stereochemical…”

Synthesis of “Garner” Aldehyde‐Derived Cyclopropylboronic Esters

“…While the isolation of the diol 5/ent-5-derived olefins 12 and 13 (69Ϫ80%) was unproblematic, the purification of ester 14 proved troublesome: chromatographic separation from side products was possible, but slow decomposition of 14 decreased the yield (63%). The transesterification with benzpinacol was a slow process, [61] presumably due to the fact that the two hydroxy groups should preferentially exist in an antiperiplanar conformation and that the rotation around the central CϪC bond is hindered. Product isolation was unproblematic, but the alkenylboronic ester 15 was obtained only in 24% yield.…”

“…Furthermore, it was a challenge to perform further transformations to produce either synthetically useful, orthogonally protected enantiomerically pure amino alcohols or amino acids. Preliminary results in this area have been published; [61] we now wish to report our investigations in full. Figure …”

Kinetic Enzymatic Resolution of Cyclopropane Derivatives

“…As a matter of fact, a first example ± prior to our own investigation [41] ± has been the bicyclo[4.1.0]heptanyl acetate (15), [40] giving modest selectivity in a transesterification reaction with npropanol in the presence of a Rhizomucor miehei lipase (RML). A more recent, impressive example was disclosed by Westermann and Krebs who synthesized enantiomerically pure cyclopropyl hemiacetals: [42] by changing the enzyme from Candida antarctica B lipase (CAL-B) to a Pseudomonas cepacia lipase (PCL; the bacterial species has been renamed to Burkholderia cepacia, however, for convenience we continue to use the traditional name), the stereochemical course of the resolution could be reversed.…”

“…Preliminary results in the area have been published; [41] we now wish to report our investigations in full.…”