Asymmetric Halocyclization of 2-Anilidostyrenes Using N-Haloamides Enabled by Chiral Anion Phase-Transfer Catalysis
Penglei Zhang1, Xue Du1, Guogang Tu1
1School of Pharmacy, Nanchang University, Nanchang 330006, China.
Abstract:
Asymmetric halogenation for efficient construction of various 4H-3,1-benzoxazine derivatives with excellent functional group tolerance using readily available N-haloamides as the halogen source and ammonium phosphate salt catalyst under mild reaction conditions has been developed. The ammonium salt catalyst loading could be reduced to 1 mol % and recycled 4 times without deterioration in reactivity and stereoselectivity. Importantly, this process features a column-purification-free operation, leading to the green and atom-economical preparation of chiral benzoxazines in good to excellent yields and high enantioselectivities.
Related Concept Videos
Halogenation of Alkenes
Consider the bromination of cyclopentene. Molecular bromine is polarized in the proximity of the π electrons of cyclopentene. An electrophilic bromine atom adds across the double bond, forming a cyclic bromonium ion intermediate.
Reduction of Alkenes: Asymmetric Catalytic Hydrogenation
The metal catalyst used can be either heterogeneous or homogeneous. When hydrogenation of an alkene generates a chiral center, a pair of enantiomeric products is expected to form. However, an enantiomeric excess of one of the products can be facilitated using an enantioselective reaction or an...
Acid Halides to Amides: Aminolysis
In the first step of the aminolysis mechanism, the amine attacks the carbonyl carbon of the acyl chloride to form a tetrahedral intermediate. In the second step, the carbonyl group is re-formed with the elimination of a chloride...
Preparation of Acid Anhydrides
The carboxylate ion acts as a nucleophile that attacks the carbonyl carbon of the acid chloride to form a tetrahedral intermediate. Subsequently, the re-formation of the carbonyl group with the loss of the chloride ion as a leaving group leads to the formation of an acid...
Acid-Catalyzed α-Halogenation of Aldehydes and Ketones
In the first step of the mechanism, the acid protonates the carbonyl oxygen resulting in a resonance-stabilized cation, which subsequently loses an α-hydrogen to form an enol tautomer. The C=C bond in an enol is highly nucleophilic because of the electron-donating nature of the –OH group. Consequently, the double bond attacks an electrophilic...
Reactions of α-Halocarbonyl Compounds: Nucleophilic Substitution


![Solid-phase Synthesis of [4.4] Spirocyclic Oximes](/_next/image?url=https%3A%2F%2Fcloudfront.jove.com%2FCDNSource%2Fteasers%2F58508.jpg&w=3840&q=50)