The oxidation of organic molecules represents a fundamentally important chemical process. Particularly important is allylic oxidation, whereby a single methylene unit is converted directly into a carbonyl group. In this communication, we report that dirhodium(II) caprolactamate [Rh2(cap)4] in combination with tert-butyl hydroperoxide (terminal oxidant) effectively catalyzes the allylic oxidation of a variety of olefins and enones. The reaction is completely selective, tolerant of air/moisture, and can be performed with as little as 0.1 mol % catalyst in minutes. A mechanistic proposal involving redox chain catalysis has been put forth, as well as evidence for the intermediacy of a higher valent dirhodium tert-butyl peroxy complex.

The development of a versatile method for the preparation of 5 to 8-membered hydroxy lactams, involving the iodine(III)-mediated oxamidation of unsaturated O-alkyl hydroxamates is described. This transformation, which is believed to proceed through the intermediacy of singlet nitrenium and bicyclic N-acyl-N-alkoxyaziridinium ions, is in most of the 22 cases examined, both stereospecific and/or highly regioselective.The reaction of singlet nitrenium ions1 with alkenes has long been known to proceed in stereospecific fashion to generate aziridinium ions.2 However, in comparison to the reaction of carbenes, their isoelectronic congeners, this process has until recently, received scant attention,3 -5 despite the growing importance of both aziridines and aziridinium ions in organic synthesis.6 While this reflects the harsh conditions traditionally required for formation of these reactive electrophiles, the iodine(III)-mediated oxidation of O-alkyl hydroxamates 1 offers convenient access to O-stabilized nitrenium ions (7 in Scheme 1). 1b Having successfully employed the cyclization of these species with arenes as a route to azaspiranes, 7 we became intrigued by the possibility that intramolecular addition of nitrenium ions generated from unsaturated hydroxamates 1 would not only yield bicyclic N-acyl-N-alkoxyaziridinium ions 4, but through concerted ring opening of these products, offer a means to accomplish cyclofunctionalization. Herein, we report the successful development of this reaction as a highly versatile method for the preparation of 5 to 8-membered hydroxy lactams 3. 8,9 Our preliminary studies focused on substrate 1a which, upon treatment with phenyliodine(III) bis(trifluoroacetate) (PIFA) in CH 2 Cl 2 , smoothly underwent cyclization to form anti-addition product 2a in high yield (eq 1). In light of the lability of this ester, a methanol-ammonia quench was employed to remove the trifluoroacetate group and provided α-hydroxyalkyl lactam 3a as a single diastereomer in excellent yield. Importantly, we have found that addition of trifluoroacetic acid to the oxamidation reaction significantly accelerates this process and, in most cases, improves its efficiency (Table 1). That acid catalysis plays a significant role in the formation of 2a is also apparent from the inhibitory effect of acid scavengers and the failure of both PhI(OAc) 2 and Pb(OAc)4 to mediate cyclofunctionalization.10 , 11wardropd@uic.edu. Supporting Information Available: Characterization, procedures and stereochemical assignments. This material is free of charge via the Internet at http://pubs.acs.org. Employing these optimal conditions, a range of unsaturated hydroxamates was screened. As is apparent from Table 1, this reaction is characterized by broad substrate scope and, in most cases, is both stereospecific and highly regioselective. In the case of 1,2-disubstituted alkenes, concerted ion pair collapse of bicyclic aziridinium ions 4c-e occurs solely at the less encumbered α position to yield α-hydroxyalkyl lactams, while bicyclo[2...

[reaction: see text] A mild, efficient, and selective aziridination of olefins catalyzed by dirhodium(II) caprolactamate [Rh(2)(cap)(4).2CH(3)CN] is described. Use of p-toluenesulfonamide (TsNH(2)), N-bromosuccinimide (NBS), and potassium carbonate readily affords aziridines in isolated yields of up to 95% under extremely mild conditions with as little as 0.01 mol % Rh(2)(cap)(4). Aziridine formation occurs through Rh(2)(5+)-catalyzed aminobromination and subsequent base-induced ring closure. An X-ray crystal structure of a Rh(2)(5+) halide complex, formed from the reaction between Rh(2)(cap)(4) and N-chlorosuccinimide, has been obtained.

A new course for undergraduate biochemistry laboratory has been developed in the Department of Chemistry at the University of Illinois at Chicago. The course is innovative pedagogically by giving students a set of relevant skills for biochemical research and then allowing them to apply those skills in designing and performing the procedures for a research-like project. The course content focuses on the pharmacologically important enzyme ␤-lactamase, which is involved in the hydrolysis of antibiotics such as penicillins and cephalosporins. Specifically, each student designs and performs site-directed mutagenesis of the enzyme ␤-lactamase and analyzes the effect of mutation on the catalytic function of the enzyme by an enzyme assay. This unique and valuable research experience greatly enhances their understanding of scientific reasoning and the research process. Evaluation of the progress also indicates successful linkage of skill-building and student-directed activities even for students with no prior experience.

The [2 þ 2]-cycloaddition reaction between ethyl glyoxylate and trimethylsilylketene is reported. Enantiomeric excesses up to 83% have been achieved with the use of only 1.0 mol % of a previously unreported chiral imidazolidinone-ligated dirhodium(II) carboxamidate catalyst. An extensive survey of chiral catalysts has shown that enantiocontrol for cycloaddition increases as the steric bulk of the ligand is increased. However, enantioselectivity is increased to 99% ee by the addition of 10 mol % of quinine as a co-catalyst with a chiral dirhodium(II) azetidinone-ligated catalyst, and there is a significant decrease in reaction time.