Prefece IX 1 Microwave Synthesis -An Introduction 1 References 5 2 Microwave Theory 11 2.1 Microwave Radiation 11 2.2 Microwave Dielectric Heating 12 2.3 Dielectric Properties 25 2.4 Microwave versus Conventional Thermal Heating 19 2.5 Microwave Effects 20 2.5.1 Temperature Monitoring in Microwave Chemistry 22 2.5.2 Thermal Effects (Kinetics) 28 2.5.3 Specific Microwave Effects 31 2.5.4 Non-Thermal (Athermal) Microwave EfFects 37 References 42 3 Equipment Review 45

Chiral nonracemic acetylenic acids of general structure 11, prepared using the Schreiber modification of the Nicholas reaction, have been converted to β-amino acid derivatives of type 12 by a two-step sequence involving Curtius rearrangement followed by oxidative cleavage of the acetylenic bond. Amino acid derivatives 12 are excellent precursors for β-lactams of the carbapenem class, including the important antibiotics thienamycin (1) and PS-5 (4).

Three-membered heterocyclic rings offer an uncommon combination of reactivity, synthetic flexibility, and atom economy. This mini review surveys a selection of the most recent advances amongst epoxides and aziridines. Emphasis is given to novel synthetic methods and new insights into existing methodologies for the selective construction and controlled reaction of the title compounds reported in the past year's literature. While not the exclusive focus of this minireview, well-represented themes in the literature include asymmetric techniques and environmentally compatible reagents.

2,3-Bis(phenylsulfonyl)-l,3-butadiene undergoes conjugate addition in the presence of carbanions giving rise to a variety of unsaturated sulfones. Reaction with lithium enolates proceeds via an allylic anionic intermediate which undergoes a subsequent elimination of phenylsulfinate anion to produce an allene. Generation of enolates from silyl enol ethers results in conjugate addition to the diene without subsequent elimination. Substituted cyclopentenyl sulfones are available via a [4 + 1] annulation reaction of the diene with various distabilized carbanions. The reaction involves a tandem addition-proton exchange-addition sequence. In the special case of 2,4-pentanedione, pyrans are formed, the isomeric identity of which depends upon the reaction conditions. 2-Alkylated 1,3dicarbonyl compounds react with the activated diene to produce substituted allenes in high yield. Phenylsulfonyl alkenyl substituted allenes were conveniently prepared by a similar protocol and were found to serve as substrates for intramolecular [2+2] cycloaddition chemistry.

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Various phenylsulfonyl allene derivatives were prepared with double bonds tethered either to the alpha-position or the gamma-position of the allene. These substrates underwent a highly regio- and stereospecific thermal [2 + 2]-cycloaddition across the nonactivated cumulene double bond, forming distal cycloadducts (i.e., 57) in the case of alpha-tethered allenes and proximal adducts (i.e., 25) in the case of gamma-tethered allenes. The mechanistic rationale for the observed stereospecificity involves initial diradical formation, followed by a rapid ring closure to the more stable cis-fused ring system. The tether may be equipped with heteroatoms, allowing for the formation of fused heterocycles (e.g., 61), and the cycloaddition can be facilitated by the introduction of sterically bulky groups and/or by conformational rigidity to the tether. Other modes of cyclization were observed in the presence of sodium benzenesulfinate or Lewis acids, in which cases polar mechanisms prevail. The chemoselectivity is reversed for [4 + 2]-cycloadditions, which prefer instead to engage the vinyl sulfone moiety, independent of whether the tether is attached to the alpha- or gamma-position of the allene.

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