Consecutive cyclization of allylaminoalkene by intramolecular aminolithiation-carbolithiation

Synthetic and Computational Study of Tin-Free Reductive Tandem Cyclizations of Neutral Aminyl Radicals

5- exo, 5- exo Cyclizations of conformationally unbiased propargylic aminyl radicals proceed with excellent yield, chemoselectivity, and diastereoselectivity under tin-free reductive cyclization conditions, regardless of the electronic environments and intermediate radical stabilization resulting from various olefin substituents. These conditions avoid the need for slow addition of initiator and reductant. By contrast, analogous 6- exo, 5- exo cyclizations require substituents capable of intermediate radical stabilization to avoid premature reduction products. These experimental results are corroborated by computations that further establish the reactivity of these aminyl radicals upon exposure to tin-free cyclization conditions.

Rare-earth metal diisopropylamide-catalyzed intramolecular hydroamination

Well-defined rare-earth metal diisopropylamide complexes provide an exemplary case study to investigate the effect of donor solvent, alkali metal, chloro co-ligands, and in situ catalyst formation.

Base-catalyzed intramolecular hydroamination of cyclohexa-2,5-dienes: insights into the mechanism through DFT calculations and application to the total synthesis of epi-elwesine

The base-catalyzed intramolecular hydroamination of 1-ethylaminocyclohexa-2,5-dienes is described. The transformation proceeds through isomerization of the cyclohexa-1,4-dienyl fragment into the corresponding conjugated 1,3-diene prior to the hydroamination step. Attaching a chiral glycinol ether auxiliary on the amino group allows the protonation to occur with complete diastereocontrol. The resulting lithium amide then adds onto the 1,3-dienyl moiety, affording the desired fused pyrrolidine ring along with the corresponding lithium allylic anion. Protonation of the latter then proceeds with high regiocontrol to favor the resulting allylic amines. In contrast, when the reaction was performed on primary amines, fused pyrrolidines bearing a homoallylic amino group were obtained. The stereochemical course of the process and determination of the reaction pathways were established based on calculations performed at the DFT level. Finally, application of the methodology to the enantioselective synthesis of (+)-epi-elwesine, a crinane alkaloid, is described.

Thieno[2,3-d]pyrimidinedione derivatives as antibacterial agents

Several thieno[2,3-d]pyrimidinediones have been synthesized and examined for antibacterial activity against a range of gram-positive and gram-negative pathogens. Two compounds displayed potent activity (2-16 mg/L) against multi-drug resistant gram-positive organisms, including methicillin resistant, vancomycin-intermediate, vancomycin-resistant Staphylococcus aureus (MRSA, VISA, VRSA) and vancomycin-resistant enterococci (VRE). Only one of these agents possessed moderate activity (16-32 mg/L) against gram-negative strains. An examination of the cytotoxicity of these agents revealed that they displayed low toxicity (40-50 mg/L) against mammalian cells and very low hemolytic activity (2-7%). Taken together, these studies suggest that thieno[2,3-d]pyrimidinediones are interesting scaffolds for the development of novel gram-positive antibacterial agents.

Aminolithiation of carbon-carbon double bonds as a powerful tool in organic synthesis

A conjugate amination of α,β-unsaturated carbonyl compounds with lithium amides has become a powerful method of N-C bond-forming reactions. Chiral ligand-controlled asymmetric version of the conjugate amination of enoates was developed for practical bench chemistry, giving the enantioenriched amination product with over 99 % ee. In situ diastereoselective alkylation of resulting lithium enolates allowed us to form vicinal N-C and C-C bonds in a one-pot operation. This protocol enabled us to realize a short-step asymmetric synthesis of otamixaban key intermediate. Treatment of product 3-benzylamino- and 3-allylaminoesters with tert-butyllithium gave five- or seven-membered lactams through [1,2]- or [2,3]-rearrangement of intermediate β-lactams. Isolated C-C double bonds were also found to accept intramolecular aminolithiation affording the corresponding hydroamination products. Chiral lithiophilic ligand-catalyzed reaction gave enantioenriched hydroamination products with high ee. Stereoselective intramolecular aminolithiation of allylaminoalkenes was coupled with subsequent carbolithiation to give doubly cyclized product amines.