Bimal K. Banik

Stereocontrol of β-lactam formation using microwave irradiation

Abstract Formation of β-lactams by the reaction of an acid chloride, a Schiff base and a tertiary amine seems to involve multiple pathways some of which are very fast at higher temperatures. When β-lactam formation is conducted in open vessels in unmodified domestic microwave ovens, high level irradiation leads to preferential formation of trans β-lactams in several cases when the Schiff base is derived from an aryl aldehyde rather than glyceraldehyde acetonide.

Microwave-Induced Organic Reaction Enhancement (More) Chemistry: Techniques for Rapid, Safe and Inexpensive Synthesis

Synthetic organic reactions have been conducted under microwave irradiation in open vessels in unaltered domestic microwave ovens. Reaction times vary from a few seconds for sub-milligram reactions to about 15 minutes for reactions carried out on a scale of hundreds of grams. Promising results have been obtained for several condensations, as well as the Bischler-Napieralski reaction, the Wolff-Kishner reduction, free radical dehalogenation reactions, and other standard synthetic operations. Rapid catalytic transfer hydrogenation using ammonium formate as the source of hydrogen has been conducted at about 100-130 °C under microwave irradiation.Meaningful, safe and inexpensive synthetic experiments for undergraduate and pre-college students have been developed and tested. The MORE chemistry techniques make it possible to use simple apparatus and very short reaction times.Commercial microwave ovens are now essential equipment in our research and teaching laboratories [1-3]. These ovens are relatively inexpensive, easy to move from one laboratory and set up in another, and safe to operate. Glass, plastics, and ceramics are essentially transparent to microwaves whereas many organic compounds are dipolar in nature and absorb microwave energy readily. We have found that untraditional experimental arrangements are possible for conducting a wide variety of organic reactions in open vessels inside domestic microwave ovens. Depending on the quantity of reactants, most reactions (on a scale of milligrams to several grams) can be completed in minutes instead of hours. One important element of our “Microwave-induced Organic Reaction Enhancement” (MORE) chemistry is the proper choice of a microwave energy transfer agent as the reaction medium.

Polyhydroxy Amino Acid Derivatives via β-Lactams Using Enantiospecific Approaches and Microwave Techniques

Abstract Enantiospecific synthesis has been developed for α-hydroxy β-lactams of predictable absolute configuration starting with readily available carbohydrates. Stereospecific approaches and microwave assisted chemical reactions have been utilized for the preparation of these 3-hydroxy-2-azetidinones and their conversion to natural or non-natural enantiomeric forms of intermediates for gentosamine, 6-epi-lincosamine, γ-hydroxythreonine, and polyoxamic acid.

Microwave-induced organic reaction enhancement chemistry.4 convenient synthesis of enantiopure α-hydroxy-β-lactams1

Abstract A convenient and rapid synthesis of enantiopure α-hydroxy-β-lactams using microwave-induced organic reaction enhancement chemistry has been developed. Reactions in domestic microwave ovens, which are very convenient and economical for small scale work in research or teaching laboratories, can also be conducted on a preparative scale of 100–500g in simple beakers or flasks.

Vinyl-β-lactams as Efficient Synthons. Eco-friendly Approaches via Microwave Assisted Reactions

Abstract Vinyl-β-lactams are efficient synthons for a variety of compounds of biomedical interest—such as isocephalosporins, carbapenem and thienamycin intermediates, and pyrrolidine alkaloids. Convenient methods are described for obtaining both enantiomers of some of these synthons. Microwave-induced Organic Reaction Enhancement (MORE) chemistry techniques allow highly accelerated synthesis of variously substituted vinyl-β-lactams using limited amounts of solvents and with efficient stereocontrol—thus achieving high ‘atom economy’. The effect (if any) of microwaves on bond angles and bond lengths and the geometry of transition states are not well understood yet. Nonetheless, reactions under microwave irradiation in open systems are rapid, safe, and cost-effective for synthetic approaches that are much more friendly to the environment than conventional processes.

Enantiopure α-hydroxy-β-lactams via stereoselective glycosylation

Abstract Stereospecific glycosylation via the Ferrier rearrangement catalyzed by iodine has been used to obtain both enantiomers of a trans 4-aryl-3-hydroxy-2-azetidinone. Unexpectedly, a rhamnal derivative had to be employed for this reaction since a glucal derivative failed to work. This synthesis complements our previously described preparation of the corresponding cis isomers by the same methodology. Thus, convenient access has become available to all four homochiral stereoisomers of α-hydroxy-β-lactams some of which are synthons for Taxol ® and analogs.

Fused tricyclic β-lactams via intramolecular aryl radical cyclization1#

Abstract Easy access to fused tricyclic β-lactams starting with o-bromobenzaldehyde and allyl amine has been devised using intramolecular aryl radical cyclization under the influence of tributyltin hydride. The major product resulted from exo cyclization leading to the formation of a 6-membered ring and thus a tricyclic β-lactam. In some cases, a minor product was a 7-membered ring-containing tricyclic β-lactam formed by endo cyclization.