Precise control of the formation of a covalent and an ionic bond in carbocation-carbanion combination reactions
摘要:
The electronic effect on the selectivity of covalent or ionic bond formation was examined for the reaction of Kuhn's anion 1- (C67H39-; tris(7H-dibenzo[c,g]fluorenylidenemethyl)methide ion) and 1-aryl-2,3-dicyclopropylcyclopropenylium ions. The carbocation stability was progressively changed by varying the substituent on the phenyl ring, while the steric effect was kept essentially unchanged. The cations having the p-chlorophenyl (2a+), phenyl (2b+), m-methylphenyl (2c+), or m,m'-dimethylphenyl (2d+) group gave a covalent product, whereas a carbocation-carbanion salt was obtained from the cations having the p-methylphenyl (2e+) or p-methoxyphenyl (2f+) group. The reduction potentials E(red) of the cations, as determined by cyclic voltammetry, showed that the formation of the covalent or ionic product is switched by a small difference in stability (less-than-or-equal-to 0.4 kcal/mol) between 2d+ and 2e+. In chloroform, the salts 1-2e+ and 1-2f+ were transformed into covalent forms 1-2e and 1-2f, which can exist only in solution. When 1-(2a-d) and 1-2e,f+ were dissolved in DMSO, equilibrium between a covalent compound and ions was established. A plot of the free energy of heterolysis DELTAG(het)-degrees for 1-(2a-f) against the E(red) of the corresponding cations 2a-f+ showed that DELTAG(het)-degrees decreases as the cation is more stabilized. The heterolysis in DMSO was shown to be enhanced by ca. 13 kcal/mol both by the steric congestion in the covalent molecules and the stabilization of the cyclopropenylium ions by solvation.
Disclosed herein are modulators of TRPV3 of formula (II):
wherein G
1
, X
1
, X
2
, X
3
, X
4
, X
5
, G
2
, R
a
, R
b
, and u are as defined in the specification. Compositions comprising such compounds and methods for treating conditions and disorders using such compounds and compositions are also presented.
A catalytic asymmetric intramolecular homologation of simple ketones with α‐diazoesters was firstly accomplished with a chiral N,N′‐dioxide–Sc(OTf)3 complex. This method provides an efficient access to chiral cyclic α‐aryl/alkyl β‐ketoesters containing an all‐carbon quaternary stereocenter. Under mild conditions, a variety of aryl‐ and alkyl‐substituted ketone groups reacted with α‐diazoester groups
Disclosed herein are modulators of TRPV3 of formula (II):
wherein G1, X1, X2, X3, X4, X5, G2, Ra, Rb, and u are as defined in the specification. Compositions comprising such compounds and methods for treating conditions and disorders using such compounds and compositions are also presented.
Chlorohydrins and oxaheterocycles are synthetically valuable building blocks for diverse natural products and therapeutic substances. A highly efficient Ir/f-phamidol-catalyzed asymmetric hydrogenation of ω-chloroketones was successfully developed, and various chlorohydrins and oxaheterocycles were obtained divergently with excellent yields and enantioselectivities (up to >99% yield and >99% ee). Synthetic