Tandem ireland-claisen rearrangement ring-closing alkene metathesis in the construction of bicyclic beta-lactam carboxylic esters

Synthesis of Tricyclic β-Lactams via Palladium Acetate-Induced Heck Reaction

Synthesis of tricyclic β-lactams via palladium acetate mediated cyclization of the unsaturated bromo β-lactam was accomplished in good yield.

Recent developments in the synthesis of condensed β-lactams

β-Lactams are important heterocycles with diverse pharmacological profiles and have emerged as useful organic synthons.

Synthesis studies on the lomaiviticin A aglycone core: development of a divergent, two-directional strategy

The enantiomer of the bicyclic lomaiviticin aglycone A core was prepared via a two-directional, divergent approach featuring (1) a double Ireland Claisen rearrangement to establish key core bonds with correct relative stereochemistry and (2) a double olefin metathesis reaction to deliver both cyclohexene rings of the target.

A synergistic approach to polycyclics via a strategic utilization of Claisen rearrangement and olefin metathesis

Olefin metathesis promoted by a well-defined metal carbene complex has evolved into an efficient method for the construction of a broad range of carbocyclic and heterocyclic rings of varying size. The synthetic potential of the olefin metathesis has been further increased by combining various other C-C bond forming processes either in tandem or in sequence. Herein, application of Claisen rearrangement and olefin metathesis to prepare various intricate and/or biologically important targets has been described.

Ring-Rearrangement Metathesis

Ring-rearrangement metathesis (RRM) refers to the combination of several metathesis transformations into a domino process, in which an endocyclic double bond of a cycloolefin reacts with an exocyclic alkene. RRM has proven to be a powerful method for the rapid construction of complex structures. The extension of the basic ring-opening-ring-closing metathesis process by further metathesis steps as well as an examination of the driving forces, limits, scope, recent advantages, and future perspectives of these domino sequences is presented with various examples, thus reflecting the high efficiency and utility of RRM in organic synthesis.

Synthesis of Diverse Macrocyclic Peptidomimetics Utilizing Ring-Closing Metathesis and Solid-Phase Synthesis

The synthesis of a range of highly functionalized peptidomimetic macrocycles has been accomplished using ring-closing metathesis and enyne tandem cross-metathesis-ring-closing metathesis reactions. This approach gives access to rigidified macrocycles modeled on the structures of cyclic peptides and designed to be biologically stable. The potential for peripheral functionalization of these templates has been demonstrated using Diels-Alder reactions, palladium(0) coupling reactions, and amide formation both in the solution phase and using polymer-supported syntheses.

Asymmetric synthesis of unusual fused tricyclic beta-lactam structures via aza-cycloadditions/ring closing metathesis

Conveniently substituted bis-beta-lactams, pyrrolidinyl-beta-lactams, and piperidinyl-beta-lactams undergo ring-closing methatesis using Grubbs' carbene, Cl(2)(Cy(3)P)(2)Ru=CHPh, to give medium-sized rings fused to bis-2-azetidinone, pyrrolidinyl-2-azetidinone, or piperidinyl-2-azetidinone systems. The diolefinic cyclization precursors can be obtained from optically pure 4-oxoazetidine-2-carbaldehydes bearing an extra alkene tether at position 1 or 3 of the beta-lactam ring via [2 + 2] cycloaddition of imino 2-azetidinones, N-metalated azometine ylide [3 + 2] cycloaddition, and subsequent N-acylation of the pyrrolidinyl nitrogen atom, or through aza-Diels-Alder cycloaddition of 2-azetidinone-tethered imines. Under standard reaction conditions, the combination of cycloaddition reactions of 2-azetidinone-tethered imines with ring-closing methatesis offers an asymmetric entry to a variety of unusual fused tricyclic 2-azetidinones bearing two bridgehead nitrogen atoms.

Easy access to N,N-bis(but-3-enyl)-, N-allyl-N-(but-3-enyl)-, and N-(but-3-ynyl)-N-(but-3-enyl)-amines

N,N-Bis(but-3-enyl)amines 5a-i were prepared in overall 74% yield from 1-(triphenylphosphoroylideneaminoalkyl)benzotriazole using an aza-Wittig reaction with aldehydes followed by a double Grignard reaction with allylmagnesium bromide. Use of vinyl or 1-propynylmagnesium bromide and allylmagnesium bromide in a sequential fashion also formed the expected doubly unsaturated amines 9a,b and 12, respectively.

Remarkable synthesis of 2-(Z)-6-(E)-4H-[1,4]-thiazepin-5-ones by zwitteronic rhodium-catalyzed chemo- and regioselective cyclohyrocarbonylative ring expansion of acetylenic thiazoles

Cyclohydrocarbonylative ring expansion of acetylenic thiazoles in the presence of CO, H(2), and catalytic quantities of the zwitterionic rhodium complex (eta(6)-C(6)H(5)BPh(3))(-)Rh(+)(1,5-COD) and triphenyl phosphite affords thiazepinones in 61 to 90% yields. This novel transformation of a 5- to a 7-membered heterocycle is readily applied to acetylenic thiazoles containing hydro, alkyl, alkyl halide, vinyl, and benzo substitutents in positions 4 and 5 of the thiazole ring in addition to alkyl-, ether-, ester-, vinyl-, and aryl-substituted alkynes at position 2.