Models for asymmetric [2+2] cycloadditions

Abstract

Supplementary Material Available: Observed and calculated structure factor amplitudes, atomic coordinates (Table I), and anisotropic temperature factors (Table II) (19 pages). Ordering information is given on any current masthead page.

Esterase-mediated synthesis of optically active GABA analogues containing a stereogenic all-carbon quaternary carbon atom

“…Finally, a bicyclic derivative, namely (1S,5S,6R)-(À)-(6-(aminomethyl)bicyclo[3.2.0]heptane-6-acetic acid, [17][18][19] is a therapeutic agent used against a variety of neurodegenerative and neuropathological disorders. Its synthesis is based on commercially available (1R,5S)-(+)-cis-bicyclo[3.2.0]hept-2-en-6-one.…”

“…Its synthesis is based on commercially available (1R,5S)-(+)-cis-bicyclo[3.2.0]hept-2-en-6-one. [19][20][21] In the frame of our research, involving the use of hydrolytic enzymes in the synthesis of chiral compounds of biological and pharmaceutical interest, and in particular of c-aminobutyric acid analogues, we developed a short and inexpensive route to a series of acyclic and cyclic b,b-disubstituted-c-aminobutyric acids using commercial esterases in the enantiodifferentiating step. This work is of interest not only for the biological potential relevance of these compounds but also for the synthetic problem associated with the obtainment of chiral compounds with a quaternary asymmetric carbon atom.…”

Cyclobutane and Cyclobutene Synthesis: Catalytic Enantioselective [2+2] Cycloadditions

“…Despite all of these efforts,t here are many useful [2+ +2] cycloadditions which do not have an enantioselective variant;f or example, several of the known transition metal catalyzed processes, [53] as well as the venerable ketene-alkene [2+ +2] cycloaddition. [54,55] In addition, the utility of these methods has only rarely been demonstrated in the synthesis of complex molecules. [22,30] Continued efforts in these areas will undoubtedly lead to fundamentally new methods and an increase in the scope and practicality of existing strategies.…”

Revisiting Keteniminium Salts: More than the Nitrogen Analogs of Ketenes

“…Noteworthy are the facts that (1) keteniminiums are more electrophilic and more reactive; [4,7,[12][13][14][15][16] (2) keteniminiums do not dimerize or polymerize (in contrast to some ketene derivatives) and can be stored in solution; [4,17] and (3) they offer an easy access to homochiral cyclobutanones as chiral substituents can be readily introduced on the nitrogen atom. [4,[13][14][15]18] In addition, the amide route to keteniminium ions (vide supra) employs inexpensive, stable, and readily available starting materials. [4,16,17] Keteniminium/olefin [2+2] cycloadditions are usually highly regioselective.…”

“…[18,29] This moiety, by its truly ancillary character, belongs to a rare class of "traceless" chiral auxiliaries. [18,29] This moiety, by its truly ancillary character, belongs to a rare class of "traceless" chiral auxiliaries.…”