Novel method for incorporating the CHF(2) group into organic molecules using BrF(3)

2-Alkyl-1,3-dithiane derivatives, easily made from alkyl bromides and the parent 1,3-dithiane, were reacted with BrF(3) to form the corresponding 1,1-difluoromethyl alkanes (RCHF(2)) in 60-75% yield. The reaction proceeds well with primary alkyl halides. The limiting step for secondary alkyl halides is the relatively low yield of the dithiane preparation. The two sulfur atoms of the dithiane are essential for the reaction.     

Hydroxide ion initiated reactions under phase transfer catalysis conditions—IV : Effect of catalyst structure

The nature of the quat-anion interactions in a PTC/OH^? system was probed by examining the reactivity and selectivity of a CA/O-ambident anion towards an alkylating agent in the presence of various quats. It is suggested that the accessibility of the positive N center of the qual for association with the anion is the major factor in determining the behavior of PTC/OH^? reactions proceeding through the Makosza mechanism.     

The mechanism of aluminum-catalyzed Meerwein-Schmidt-Ponndorf-Verley reduction of carbonyls to alcohols

The mechanistic details of the Meerwein-Schmidt-Ponndorf-Verley (MSPV) reduction of ketones to the corresponding alcohols were investigated both experimentally and computationally. Density functional theory (DFT) was used to assess the energetics of several proposed pathways (direct hydrogen transfer, hydridic, and radical). Our results demonstrate that a direct hydrogen transfer mechanism involving a concerted six-membered ring transition state is the most favorable pathway for all calculated systems starting from a small model system and concluding with the experimentally investigated BINOLate/Al/(i)PrOH/MePhC=O system. Experimental values for the activation parameters of acetophenone reduction using the BINOLate/Al/(i)PrOH system (DeltaG# = 21.8 kcal/mol, DeltaH# = 18.5 kcal/mol, DeltaS# = -11.7 au) were determined on the basis of kinetic investigation of the reaction and are in good agreement with the computational findings for this system. Calculated and experimental kinetic isotope effects support the concerted mechanism.     

Tandem one-Pot palladium-catalyzed reductive and oxidative coupling of benzene and chlorobenzene

The in situ combination of oxidative coupling of benzene to biphenyl and reductive coupling of chlorobenzene (also to biphenyl) using palladium catalysts (Pd(2+)/Pd(0)) is described. In each cycle, the reductive process regenerates the catalyst for the oxidative process and vice versa. Kinetic investigations show that the reaction rate depends on [C(6)H(6)], [C(6)H(6)Cl], and catalyst loading, with E(a)() = 13 kcal mol(-)(1). The reduced palladium catalyst undergoes deactivation through aggregation and precipitation, but it is observed that during this deactivation process the Pd(0) becomes an active catalyst for the reductive coupling of chlorobenzene. Accordingly, while Pd(0)/C particles are inactive, Pd(0) colloids do catalyze the tandem reaction. Conversion is increased in the presence of a phase-transfer catalyst, presumably due to stabilization of the active Pd(0) clusters. The two halves of the catalytic cycle are examined in the light of previous research, regarding analogous oxidative and reductive coupling reactions, using stoichiometric amounts of PdCl(2) and Pd(0), respectively. The roles of homogeneous PdCl(2) and Pd(0) clusters are discussed.     

Bromofluorination of olefins using BrF3; an efficient route for fluoroalkenes and fluoroamines

A variety of alkenes and α,β-unsaturated carbonyls were reacted with BrF₃ to form vicinal bromofluoro compounds. In most cases, the reactions followed a Markovnikov regioselectivity and anti-addition stereospecifity. They proceeded well even with deactivated olefins in around 70% yield. The bromofluoro compounds served as starting materials for the synthesis of fluoroalkenes and fluoroamines.     

Quantitative NMR spectrometry of phase-transfer catalysts: Part 1. Determination of Extraction Constants and Water of Hydration

Proton magneticf resonance spectrometry was applied for evaluation of the distribution ratios and apparent extraction constants of tetraalkylammonium and tetraalkylphosphonium salts in two liquid-phase systems. Triethylbenzyl- and tetrabutylammonium chloride in dichloromethane and chlorobenzene, respectively, were shown to be salted out in the presence of aqueous sodium hydroxide solutions. ¹H-n.m.r. spectrometry was also used to determine the degree of hydration of quaternary onium salts in two-phase systems. The results were compatible with those obtained by the Karl Fischer method.     

On the mechanism of palladium-catalyzed coupling of haloaryls to biaryls in water with zinc

[reaction: see text] Kinetics and process parameters of coupling and hydro-dehalogenation reactions of chloroaryls are studied in the presence of zinc, water, and catalytic Pd/C. Good yields are obtained for the coupling of chlorobenzene, 4-chlorotoluene, and 4-chloro-1,1,1-trifluorotoluene. It is shown that water is actually one of the reagents, reacting with zinc in the presence of palladium to give zinc oxide and hydrogen gas, which then regenerates the Pd0 catalyst for the coupling reaction.     

12-Substituted-13,14-dihydroretinols designed for affinity labeling of retinol binding- and processing proteins

All-trans- and 11-cis-retinol derivatives substituted with various electron-withdrawing groups at C₁₂ were designed to be affinity labels for retinol binding and processing proteins. Unlike other non-selective highly reactive affinity labels, these compounds carry a Michael acceptor type substitution at C₁₂ of the polyene chain. Therefore, they are expected to be highly selective towards such proteins that have a nucleophilic residue near the C₁₁ position of their retinol ligand. The synthetic route for these compounds is based on the Emmons-Horner reaction of a C15 aldehyde with an appropriate phosphonate bearing the desired electron-withdrawing group to be incorporated at the C₁₂ position of the retinol skeleton.