Synthesis of quinolines via copper-catalyzed domino reactions of enaminones.

Quinoline derivatives were obtained from enaminones and 2-bromo- or 2-iodobenzaldehydes via copper-catalyzed domino reactions consisting of the aldol reaction, C(aryl)-N bond formation and elimination. The electronic effect of aldehydes played a major role in the reaction outcome. Two simple protocols are disclosed to achieve various quinolines from both cyclic and acyclic enaminones in good yields.

Syntheses of quinazolinones from 2-iodobenzamides and enaminones via copper-catalyzed domino reactions.

N-Substituted 2-iodobenzamides and enaminones undergo cascade transformations to achieve quinazolinones via a copper-catalyzed Ullmann-type coupling, a Michael addition and a retro-Mannich reaction. A unique stereochemical feature of this domino process was that Z-enaminones reacted without external ligands, whereas E-enaminones required the assistance of ligands.

Chiral N-Heterocyclic Carbene Catalyzed Annulations of Enals and Ynals with Stable Enols: A Highly Enantioselective Coates-Claisen Rearrangement.

A combination of a chiral N-heterocyclic carbene catalyst and α,β-unsaturated aldehyde leads to a catalytically generated α,β-unsaturated acyl azolium, which participates in a highly enantioselective annulation to give dihydropyranone products. This full account of our investigations into the scope and mechanism of this reaction reveals the critical role of both the type and substitution pattern of the chiral triazolium precatalyst in inducing and controlling the stereochemistry. In an effort to explain why stable enols such as naphthol, kojic acid, and dicarbonyl are uniquely efficient, we have postulated that this annulation occurs via a Coates-Claisen rearrangement that invokes the formation of a hemiacetal prior to a sigmatropic rearrangement.

Chiral N-heterocyclic carbene-catalyzed generation of ester enolate equivalents from {alpha},{beta}-unsaturated aldehydes for enantioselective Diels-Alder reactions.

The catalytic generation of chiral ester enolate equivalents from α,β-unsaturated aldehydes with chiral N-hetereocyclic carbene catalysts makes possible highly enantioselective hetero-Diels-Alder reactions. The reactions proceed under simple, mild conditions with both aliphatic and aromatic substituted enals as substrates. Previous attempts to employ these starting materials as enolate precursors gave structurally different products via catalytically generated homoenolate equivalents.

An enantioselective Claisen rearrangement catalyzed by N-heterocyclic carbenes.

In the presence of a chiral azolium salt (10 mol %), enols and ynals undergo a highly enantioselective annulation reaction to form enantiomerically enriched dihydropyranones via an N-heterocyclic carbene catalyzed variant of the Claisen rearrangement. Unlike other azolium-catalyzed reactions, this process requires no added base to generate the putative NHC-catalyst, and our investigations demonstrate that the counterion of the azolium salt plays a key role in the formation of the catalytically active species. Detailed kinetic studies eliminate a potential 1,4-addition as the mechanistic pathway; the observed rate law and activation parameters are consistent with a Claisen rearrangement as the rate-limiting step.

Stereodivergency of triazolium and imidazolium-derived NHCs for catalytic, enantioselective cyclopentane synthesis.

Chiral triazolium- and imidazolium-derived N-heterocyclic carbene catalysts promote the direct annulation of alpha,beta-unsaturated aldehydes and achiral alpha-hydroxy enones to afford cyclopentane-fused lactones with high enantioselectivity. Remarkably, otherwise structurally identical imidazolium and triazolium precatalysts afford different major products. These studies provide both an efficient entry to valuable chiral structures and a dramatic demonstration of stereodivergency of chiral imidazolium versus triazolium-derived N-heterocyclic carbene catalysts.

Synthesis of an N-mesityl substituted chiral imidazolium salt for NHC-catalyzed reactions.

A new synthetic approach to chiral imidazolium salts makes possible the first synthesis of an N-mesityl substituted, aminoindanol-derived N-heterocyclic carbene precursor, 1.ClO4. The successful synthesis allows the first direct comparison of otherwise identical imidazolium and triazolium precursors across a number of NHC-catalyzed processes.

A new pyrone derivative from the endophytic fungus Penicillium paxilli PSU-A71.

One new pyrone derivative, named penicillone (1), together with paxilline, pyrenocines A (2) and B (3) were isolated from the endophytic fungus Penicillium paxilli PSU-A71. The structures were elucidated by spectroscopic methods. Pyrenocine B (3) mildly inhibited the growth of Microsporum gypseum SH-MU-4 with a MIC value of 32 microg/ml.

Synthesis of oligosubstituted bullvalones: shapeshifting molecules under basic conditions.

Oligosubstituted bullvalones were synthesized in eight steps from 2,6-cycloheptadienone via a unique Lewis acid catalyzed intramolecular cyclopropanation of a stabilized sulfur ylide, leading directly to the tetracyclic cage structure. Upon exposure to base, the substituted bullvalones tautomerized to a hydroxybullvalene, which underwent dynamic interconversion into numerous, structurally distinct bullvalones. This system represents a "self-contained" dynamic combinatorial library in which the dynamic nature can be modulated by external reagents.