Alkyne-Co(2)(CO)(6) Complexes in the Synthesis of Fused Tricyclic beta-Lactam and Azetidine Systems(,)(1)

Gold-Catalyzed Nucleophilic Ring-Opening Reaction of 2-Alkynylazetidines with Alcohols

The reaction of 2-alkynylazetidines and alcohols with a gold catalyst is described. A variety of substituted δ-amino-α,β-unsaturated ketones were synthesized via gold-promoted nucleophilic attack of alcohols followed by ring-opening of azetidine ring.

β-Lactam and penicillin substituted mesoionic metal carbene complexes

1,2,3-Triazolylidene MIC M-complexes (M = Au, Pd, Pt) having 2-azetidinones and penicillin G substituents at the triazole ring were prepared by CuAAC on 2-azetidinones having a terminal alkyne tethered at N1, followed by alkylation of the 1,2,3-triazole ring and transmetallation [Au(I), Pd(II) and Pt(II)]. The Au-MIC complexes efficiently catalyze the regioselective cycloisomerization of enynes, while the Pt-MIC complexes were efficient catalysts in hydrosilylation reactions.

Bio-Organometallic Derivatives of Antibacterial Drugs

Overuse and misuse of antibacterial drugs has resulted in bacteria resistance and in an increase in mortality rates due to bacterial infections. Therefore, there is an imperative necessity of new antibacterial drugs. Bio-organometallic derivatives of antibacterial agents offer an opportunity to discover new active antibacterial drugs. These compounds are well-characterized products and, in several examples, their antibacterial activities have been studied. Both inhibition of the antibacterial activity and strong increase in the antibiotic activity of the parent drug have been found. The synthesis of the main classes of bio-organometallic derivatives of these drugs, as well as examples of the use of structure-activity relation (SAR) studies to increase the activity and to understand the mode of action of bio-organometallic antimicrobial peptides (BOAMPs) and platensimicyn bio-organometallic mimics is presented in this article.

Dicobalt hexacarbonyl complexes of alkynyl imines in a sequential Staudinger/Pauson-Khand process. A route to new fused tricyclic beta-lactams

Dicobalt hexacarbonyl complexes of alkynyl imines were allowed to react with ketenes via Staudinger reaction. Sequential [2 + 2] cycloaddition/Pauson-Khand reaction led to structurally new fused-tricyclic beta-lactams and fused-azabicyclic cyclopentenones. Chemoselectivity, scope, and limitation of the process were investigated.

Diastereoselective [2+2]-Cycloaddition Reactions of Unsymmetrical Cyclic Ketenes with Imines: Synthesis of Modified Prolines and Theoretical Study of the Reaction Mechanism

The synthesis of enantiomerically pure modified proline derivatives was achieved by using spiro beta-lactams as starting material that were prepared in turn by the [2+2]-cycloaddition of unsymmetrical cyclic ketenes with optically active imines. A theoretical study of the [2+2]-cycloaddition reaction, using density-functional methods, gave insights on the origin of the observed stereoselectivity of the Staudinger reaction. The spiro beta-lactams were transformed in the N-Boc derivatives and subjected to nucleophilic ring opening, affording the corresponding enantiomerically pure modified proline derivatives, isolated as orthogonally protected compounds.

Coupling reactions of alpha-(N-carbamoyl)alkylcuprates with enol triflates derived from cyclic beta-keto esters: A facile approach to gamma-carbamoyl-alpha,beta-enoates

alpha-(N-Carbamoylalkyl)cuprates couple with enol triflates derived from carbocyclic and heterocyclic (i.e., piperidinones) beta-keto esters. Product yields are higher with the alkyl(cyano)cuprates [i.e., RCu(CN)Li, 56-93%] than with the dialkylcuprate reagents (i.e., R(2)CuLi.LiCN). An enol nonaflate works as well as the corresponding enol triflate. A facile synthetic route to gamma-amino alpha,beta-enoates not readily prepared from gamma-keto-alpha,beta-enoates is thus established. The gamma-amino-alpha,beta-enoates, available via N-Boc deprotection, can be cyclized to annulated pyrrolin-2-ones.

Catalytic diastereoselective Pauson-Khand reaction: an efficient route to enantiopure cyclopenta[c]proline derivatives

Cyclopenta[c]proline derivatives were synthesized in a stereocontrolled manner and in good yields via catalytic Pauson-Khand reactions. The starting materials, optically pure enyne amino acid derivatives, can be easily prepared by an alkenylboronic acid-mediated Mannich-type reaction. [reaction: see text]

Additions of allenyl/propargyl organometallic reagents to 4-oxoazetidine-2-carbaldehydes: novel palladium-catalyzed domino reactions in allenynes

Metal-mediated carbonyl allenylation and propargylation of 4-oxoazetidine-2-carbaldehydes were investigated in aqueous environment. Different propargyl bromide and metal promoters showed varied regio- and stereoselectivities on product formation. In addition, an unprecedented one-pot stereoselective synthesis of beta-chlorinated allylic alcohols, which can also be considered as functionalized allylsilanes, has been developed, which involves tin(IV) chloride-mediated reaction of propargyltrimethylsilane and 4-oxoazetidine-2-carbaldehydes. Some of the resulting coupling products were submitted to transition metal catalyzed reactions, such as the allenic Pauson-Khand and palladium-catalyzed reactions, leading to novel fused or bridged tricyclic beta-lactams. Remarkably, a novel domino process, namely the allene cyclization/intramolecular Heck reaction was found. A likely mechanism for the cascade reaction should involve an intramolecular cyclization on a (pi-allyl)palladium complex and a Heck-type reaction.

A beta-lactam-based stereoselective access to beta,gamma-dihydroxy alpha-amino acid-derived peptides with either alpha,beta-like or unlike configurations

A concise access to alpha,beta-dihydroxy alpha-amino acid-derived N-carboxy anhydrides (NCAs) with either like or unlike relative configuration is described. The key steps of the synthetic route are the preparation of the nonracemic 4-alkenyl beta-lactams, through either Horner-type olefination of a common 4-formyl beta-lactam or the Corey-Winter alkene synthesis applied to 4-dihydroxyalkyl beta-lactams, followed by the Sharpless AD reaction, and a subsequent ring expansion of the corresponding 4-substituted 3-hydroxy beta-lactams promoted by TEMPO. The opening of thus-prepared NCAs upon treatment with different O- and N-nucleophiles, including alpha-amino esters which lead to peptides, has also been studied under various reaction conditions.

Endo-selective intramolecular Pauson-Khand reactions of gamma-oxygenated-alpha,beta-unsaturated phenylsulfones

A wide variety of 1,6-enynes and 1,7-enynes incorporating gamma-oxygenated-alpha,beta-unsaturated phenylsulfone moieties have readily been prepared by piperidine-promoted condensation of the corresponding alkynyl aldehyde with phenylsulfonyl-(p-tolylsulfinyl)methane and further protection of the hydroxyl group. Despite the enduring claim concerning the unsuitability of electronically deficient olefins in Pauson-Khand reactions, we report that these 1-sulfonylated enynes are excellent substrates in intramolecular Pauson-Khand reactions under both thermal and amine N-oxide-promoted conditions. Moreover, in contrast with the usual exo-selective Pauson-Khand cyclization of allylic substituted enynes, the reactions of these 1-sulfonylated-3-oxygenated enynes occur with a moderate or high endo selectivity. The evaluation of the chemical and stereochemical scope of the process in comparison with the Pauson-Khand cyclization of non-sulfonylated enynes, its application to the stereoselective preparation of optically pure C6-substituted bicyclo[3.3.0]oct-1-en-3-ones, and the interpretation of the stereochemical outcome are also discussed.

Diastereoselective formation of 5-vinylcyclopentenes from 1, 6-enynes: cobalt-mediated C-H allylic activation and formal 5-endo-Dig cyclization

A novel intramolecular cyclization reaction mediated by dicobalt octacarbonyl (Co(2)(CO)(8)) is reported. Thermolysis in an argon atmosphere transforms the cobalt complex of 1-trimethylsilyl-6-hepten-1-ynes into 1-trimethylsilyl-5-vinylcyclopentenes in good yield and in a highly diastereoselective manner. This formal 5-endo-dig cyclization is proposed to proceed via an allylic C-H oxidative addition.

Stereoselective Synthesis of Fused Bicyclic beta-Lactams through Radical Cyclization of Enyne-2-azetidinones(1)

A convenient, stereoselective entry to racemic and enantiomerically pure fused bicyclic beta-lactams has been developed that involves the radical-mediated cycloisomerization of easily available monocyclic enyne-beta-lactams as the key synthetic step. These compounds are obtained provided that an activated double bond is present as a radical acceptor. In the absence of this condition, new forms of reactivity were observed, including C3-C4 bond cleavage of the beta-lactam ring to yield tetrahydropyridine derivatives and 1,5-radical translocation to yield new bicyclic derivatives. Some simple transformations were tested on representative examples of the different types of bicyclic systems prepared to demonstrate their potential as intermediates in the preparation of other differently functionalized systems.