Wenzeng Duan

Enantioselective β-Boration of Acyclic Enones by a [2.2]Paracyclophane-Based N-Heterocyclic Carbene Copper(I) Catalyst

A new planar and centrally chiral bicyclic 1,2,4-triazolium salt has been synthesized from [2.2]paracyclophane and phenylglycinol. The N-heterocyclic carbene (NHC) copper(I) complex generated in situ by the reaction of the triazolium salt and Cu(2)O was an efficient catalyst for the asymmetric β-boration of acyclic enones, producing β-boryl ketones in high yields and enantioselectivities.

Asymmetric β-Boration of α,β-Unsaturated N-Acyloxazolidinones by [2.2]Paracyclophane-Based Bifunctional Catalyst

An efficient copper-catalyzed asymmetric conjugate boration has been achieved by exploiting a new planar and central chiral bicyclic triazolium ligand. This protocol was highly efficient and gave a variety of chiral secondary alkylboronates in 97-99% ee. A preliminary mechanistic study supports the bifunctional nature of the catalyst.

Design and Synthesis of Planar Chiral Heterocyclic Carbene Precursors Derived from [2.2]Paracyclophane

A unique family of planar chiral symmetrical N-heterocyclic carbene precursors with restricted flexibility derived from [2.2]paracyclopane were obtained by a new synthetic route. The resolution of 4-amino-13-bromo[2.2]paracyclophane was achieved with relatively high efficiency. Starting from (4 S p,13 R p)-4-amino-13-bromo[2.2]paracyclophane, the planar chiral pseudogem-disubstituted [2.2]paracyclophanyl dihydroimidazoliums were prepared in a four-step sequence with good yields. The resulting dihydroimidazolium salts were fully characterized with a series of methods including single-crystal X-ray diffraction technique.

SYNTHESIS OF PLANAR CHIRAL (2.2)PARACYCLOPHANYL IMIDAZO(1,5-a) PYRIDINIUM SALTS FOR THE RHODIUM- CATALYZED ASYMMETRIC ARYLATION

Abstract Several novel flexibility-restricted imidazo[1,5-a]pyridinium triflates (abbreviated as imidazolium salts) were synthesized from (4S p,13R p)-(−)-4-amino-13-bromo[2.2]paracyclophane and pyridylaldehyde. These imidazolium salts can be used as nitrogen-containing heterocyclic carbene precursors in asymmetric catalysis and here they are applied in the Rh-catalyzed asymmetric 1,2-addition of arylboronic acids to aldehydes. After optimizing the catalytic situations and testing a series of substrates, moderate enantioselectivity and good yield were obtained. GRAPHICAL ABSTRACT

Synthesis of Cyclophanes with Planar and Helical Chirality

Novel helical macrocyclic imines derived from planar chiral [2.2]paracyclophane were synthesized. The chiroptical properties of the enantiopure compounds were investigated and their absolute configurations were assigned.

Planar chirality change in dediazoniation reactions of paracyclophanes and mechanistic implication.

Dediazoniation reactions of (S(p))-4-bromo-13-[2.2]paracyclophanyldiazonium fluoborate 2a through a heterolytic cleavage process gave products with partial racemization. In contrast, dediazoniation reactions of (S(p))-2a undergoing a nonheterolytic cleavage process afforded products with retention of configuration. A key intermediate, the bromonium cation B, caused the racemization. The unexpected racemization allowed the mechanisms of the dediazoniation reaction to be probed.

5-Benzoyl-13-bromo-4-hy­droxy[2.2]paracyclo­phane

The title compound, C23H19BrO2, was synthesized from 13-bromo-4-hydroxy[2.2]paracyclophane and benzoyl chloride. The hydroxy and carbonyl groups are involved in intramolecular O—H⋯O hydrogen bonding. The crystal packing exhibits weak C—H⋯O interactions, which link the molecules into sheets parallel to the bc plane.

12,12′-[2,2′-Oxybis(ethane-2,1-di­yl)bis­(­oxy)]bis­[(R p)-4-bromo­[2.2]paracyclo­phane]

The title compound, C36H36Br2O3, was synthesized from (R p)-4-bromo-12-hydroxy[2.2]paracyclophane and oxydiethane-2,1-diyl bis(4-methylbenzenesulfonate). The crystal packing exhibits a short O⋯Br interaction [Br⋯O = 3.185 (3) Å] and a weak intermolecular C—H⋯O contact.

2-Methyl­benzimidazolium nitrate

In the title compound, C8H9N2 +·NO3 −, intermolecular N—H⋯O hydrogen bonds join the molecules into a chain extending along the b axis.

1,5-Bis[(E)-cyclo-pentyl-idene]thio-carbono-hydrazide.

In the title molecule, C11H18N4S, an intramolecular N—H⋯N hydrogen bond [N⋯N = 2.558 (3)Å] is observed. The two cyclopentyl rings are disordered between two conformations in 1:1 and 2:1 ratios. In the crystal structure, weak intermolecular N—H⋯S hydrogen bonds [N⋯S = 3.547 (3) Å] link pairs of molecules into centrosymmetric dimers.