Carbon-carbon bond forming reactions mediated by silicon Lewis acids.

Versatile roles of Lewis acids in the reactions of allylic tin compounds

A concise approach to the tetrahydroxanthone natural products employing vinylogous addition of siloxyfurans to benzopyryliums and a late-stage Dieckmann cyclization has been developed. With this methodology, chiral, racemic forms of the natural products blennolides B and blennolide C have been synthesized in a maximum of four steps from a 5-hydroxychromone substrate. The regio- and diastereoselectivity of the vinylogous additions was probed using computational studies, which suggested the involvement of Diels-Alder-like transition states.

Vinylogous addition of siloxyfurans to benzopyryliums: a concise approach to the tetrahydroxanthone natural products.

Synthesis and structure–activity relationships of 2-vinylchroman-4-ones as potent antibiotic agents

A Versatile and Efficient Synthesis of Annulated Cyclopentanes by Stereoselective [3 + 2] Cycloaddition of Allylsilanes and Cycloalkenyl Methyl Ketones

The mechanism we propose for the cyclopentane annulation is the following one. The allylic reagent (5D) attacks the siloxypyrylium salts (2a,b) at the C2 position, giving the intermediate carbocation (B) which is stabilized by the trimethylsilyl and the methyl group. Attack by the emerging enolate at C 3 , forms the five-membered ring compound (8a,b). Generally, electrophiles attack allylic silanes anti to the silyl group. Since there is undoubtedly interaction with the silicon in the transition state, the stereochemistry of the bridged intermediate (B) should be trans geometry due to stereoelectronic effect and allylic 1,3-strain. In the reaction of 2a, the favored pathway is cyclization. However, competition between cyclization and desilylation was observed in 2b due to steric hindrance between the two methyl groups at the step of cyclization

Tandem reactions in 4-siloxy-1-benzopyrylium salts : introduction of substituents and cyclohexene and cyclopentane annulation in chromones

Diels-Alder reactions of 2-[(trialkylsilyl)oxy]pyrylium cations of 2H-pyran-2-one and 2H-1-benzopyran-2-one derivatives

The reactions of allylstannanes with 4-siloxy-1-benzopyrylium salts gave the corresponding allylated derivatives more smoothly than allylsilanes. Similar reactions with 3-trimethylsilyl-1-butene afforded unexpected five-membered ring adducts in 87% and 37% yields, respectively.

Y.-G. Lee

Papers

Tandem reactions in 4-siloxy-1-benzopyrylium salts : introduction of substituents and cyclohexene and cyclopentane annulation in chromones

Diels-Alder reactions of 2-[(trialkylsilyl)oxy]pyrylium cations of 2H-pyran-2-one and 2H-1-benzopyran-2-one derivatives

Reactions of 4-siloxy-1-benzopyrylium salts with allylsilane and allylstannane reagents.

Reactions of 4-Siloxy-1-benzopyrylium Salts with Allylsilane and Allylstannane Reagents.

Diels-Alder Reactions of 2-((Trialkylsilyl)oxy)pyrylium Cations of 2H- Pyran-2-one and 2H-1-Benzopyran-2-one Derivatives.