2001, in press

Practical synthesis and cytotoxic evaluation of the pyrazino[1,2-b]-isoquinoline ring system

A multicomponent three-step synthesis of pyrazino[1-2b]isoquinolines is described. A preliminary cytotoxic screening against cancer cell lines was performed.

A concise, convergent total synthesis of monocerin

A concise and convergent eight-step synthesis of the antifungal metabolite monocerin 1 is reported. The key step involves an allylsilane metathesis/aldehyde condensation sequence to establish the core 2,3,5-trisubstituted tetrahydrofuran. End-game approaches based around intramolecular Heck chemistry revealed an interesting example of formal 6-endo cyclisation, the origin of which was probed using model substrates. The synthesis was ultimately completed by a strategy involving stepwise oxidative cleavage of the C3-ethenyl substituent.

Palladium-Catalyzed Addition of Nitrogen Pronucleophiles to Alkylidenecyclopropanes

The inter- and intramolecular additions of cyclic amides (nitrogen pronucleophiles) to methylenecyclopropanes proceeded smoothly in the presence of catalytic amounts of Pd(PPh(3))(4), affording the corresponding hydroamination products in good to high yields with high regioselectivities. The ring opening of methylenecyclopropanes occurred at the distal position of the cyclopropane ring.

Palladium-Catalyzed Tandem Cyclization/Suzuki Coupling of 1,6-Enynes: Reaction Scope and Mechanism

A palldium(0)-catalyzed tandem cyclization/Suzuki coupling reaction of various 1,6-enyne substrates was developed. This Pd-catalyzed enyne cyclization reaction represents a new process for the synthesis of stereodefined alpha-arylmethylene-gamma-butyrolactones, lactams, multifunctional tetrahydrofurans, pyrrolidines, and cyclopentanes. The mechanism of the reaction was studied by the employment of different enyne isomers and boronic acids; a pi-allyl palladium intermediate was suggested to explain the formation of the cyclic products. The stereochemistry of this reaction can be well explained by a chairlike transition state.

Amines made easily: a highly selective hydroaminomethylation of olefins

A highly chemo- and regioselective hydroaminomethylation of simple as well as functionalized alpha-olefins using a cationic rhodium precatalyst together with Xantphos as ligand is reported. Studies of the influence of ligands and reaction conditions led to an unprecedented selective hydroaminomethylation procedure. The novel procedure constitutes an economically attractive and environmentally favorable synthesis of secondary and tertiary aliphatic amines.

Palladium-catalyzed asymmetric arylation, vinylation, and allenylation of tert-cyclobutanols via enantioselective C-C bond cleavage

A novel enantioselective C-C bond cleavage has been achieved using palladium catalysts and chiral N,P-bidentate ligands in the asymmetric arylation, vinylation, and allenylation of tert-cyclobutanols. In these reactions, the enantioselective beta-carbon elimination of Pd(II) alcoholate formed in situ is the key step. Treatment of tert-cyclobutanols with arylating reagents in toluene in the presence of Pd(OAc)(2), a chiral ferrocene-containing N,P-bidentate ligand, and Cs(2)CO(3) affords optically active gamma-arylated ketones in excellent yields with high enantioselectivity (up to 95% ee). When vinylating reagents are used in place of arylating ones, the asymmetric vinylation also proceeds to afford optically active gamma-vinylated ketones in high yields with good to high enantioselectivity. When propargylic acetates are used, which are known to generate (sigma-allenyl)palladium complexes with Pd(0) species, asymmetric allenylation occurs to afford optically active gamma-allenylated ketones in moderate to good yields with moderate to high enantioselectivity.