Alkynes as Synthetic Equivalents to Stabilized Wittig Reagents: Intra- and Intermolecular Carbonyl Olefinations Catalyzed by Ag(I), BF3, and HBF4
摘要:
The first use of cationic silver (AgSbF4) as a catalyst for intra- and intermolecular alkyne-carbonyl coupling to form conjugated enones is described, and a comparison to corresponding Bronsted acid (HBF4) and Lewis acid (BF3) catalyst systems is made. Notably, intermolecular coupling proceeds stereoselectively to afford the corresponding trisubstituted enones as single geometrical isomers. This transformation represents a completely atom economical alternative to the use of stabilized Wittig reagents in carbonyl olefination and may be viewed as a formal alkyne-carbonyl metathesis.
Additive and Medium Effects on Lewis Acid-Promoted Cationic .pi.-Cyclizations of Alkenyl- and Alkynylcyclopentane-1,3-diones
摘要:
The effects of nucleophilic additives, Lewis and Bronsted acids, and solvents on BF3.Et(2)O-promoted cationic pi-cyclizations of alkynyl- and alkenylcyclopentane-1,3-diones are reported. The rates and selectivities of alkynyl dione cyclizations were significantly effected by the addition of external nucleophiles or water, and the regioselectivity of cyclization was effected by the choice of reaction solvent. Cyclizations of alkenyl diones, which fail under standard non-nucleophilic conditions, were found to be successful in the presence of added nucleophiles or with Lewis acids other than BF3.Et(2)O. The usefulness of these cationic pi-cyclizations for producing bicyclic ring systems of various functionality was also explored.
Additive and Medium Effects on Lewis Acid-Promoted Cationic .pi.-Cyclizations of Alkenyl- and Alkynylcyclopentane-1,3-diones
作者:Aaron Balog、Steven V. Geib、Dennis P. Curran
DOI:10.1021/jo00107a012
日期:1995.1
The effects of nucleophilic additives, Lewis and Bronsted acids, and solvents on BF3.Et(2)O-promoted cationic pi-cyclizations of alkynyl- and alkenylcyclopentane-1,3-diones are reported. The rates and selectivities of alkynyl dione cyclizations were significantly effected by the addition of external nucleophiles or water, and the regioselectivity of cyclization was effected by the choice of reaction solvent. Cyclizations of alkenyl diones, which fail under standard non-nucleophilic conditions, were found to be successful in the presence of added nucleophiles or with Lewis acids other than BF3.Et(2)O. The usefulness of these cationic pi-cyclizations for producing bicyclic ring systems of various functionality was also explored.
Alkynes as Synthetic Equivalents to Stabilized Wittig Reagents: Intra- and Intermolecular Carbonyl Olefinations Catalyzed by Ag(I), BF<sub>3</sub>, and HBF<sub>4</sub>
作者:Jong Uk Rhee、Michael J. Krische
DOI:10.1021/ol050838x
日期:2005.6.1
The first use of cationic silver (AgSbF4) as a catalyst for intra- and intermolecular alkyne-carbonyl coupling to form conjugated enones is described, and a comparison to corresponding Bronsted acid (HBF4) and Lewis acid (BF3) catalyst systems is made. Notably, intermolecular coupling proceeds stereoselectively to afford the corresponding trisubstituted enones as single geometrical isomers. This transformation represents a completely atom economical alternative to the use of stabilized Wittig reagents in carbonyl olefination and may be viewed as a formal alkyne-carbonyl metathesis.