P(RNCH(2)CH(2))(3)N-catalyzed 1,2-addition reactions of activated allylic synthons.

Activated allylic compounds of the type RCH:CHCH(2)Z (Z = CN, CO(2)Me) react efficiently with aromatic aldehydes in the presence of 20-40 mol % of P(R'NCH(2)CH(2))(3)N at -94 to -63 degrees C. Both R = H and R = Me lead exclusively to alpha-addition products. When R = H and Z = CN, an allylic transposition occurs to afford a Baylis-Hillman product as the only product.     

Highly active palladium catalysts supported by bulky proazaphosphatrane ligands for Stille cross-coupling: coupling of aryl and vinyl chlorides, room temperature coupling of aryl bromides, coupling of aryl triflates, and synthesis of sterically hindered biaryls

A family of proazaphosphatrane ligands [P(RNCH2CH2)2N(R'NCH2CH2): R = R' = i-Bu, 1; R = Bz, R' = i-Bu, 3; R = R' = Bz, 4] for palladium-catalyzed Stille reactions of aryl chlorides is described. Catalysts derived from ligands 1 and 4 efficiently catalyze the coupling of electronically diverse aryl chlorides with an array of organotin reagents. The catalyst system based on the ligand 3 is active for the synthesis of sterically hindered biaryls (di-, tri-, and tetra-ortho substituted). The use of ligand 4 allows room-temperature coupling of aryl bromides and it also permits aryl triflates and vinyl chlorides to participate in Stille coupling.     

P(CH(3)NCH(2)CH(2))(3)N as a dehydrobromination reagent: synthesis of vitamin A derivatives revisited.

Although P(CH(3)NCH(2)CH(2))(3)N (1) was found to be less effective than 1,5-diazabicyclo[4.3.0]non-5-ene (DBN) or 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) in the removal of hydrogen bromide from vitamin A intermediates 13-cis-10-bromo-9,10-dihydroretinyl acetates (6) and 14-bromo-9,14-dihydroretinyl acetate (11) when the reaction was carried out in refluxing benzene, in acetonitrile at room temperature it was superior to DBN and DBU. A (31)P NMR study of this reaction suggests that the carbanion generated from acetonitrile-d(3) in the presence of 1 is the basic species that initiates the elimination step. Diastereoselectivity of the nucleophilic addition of (Z)-HC triple bond C(CH(3))=CHCH(2)OH to the carbonyl group of (E)-2-methyl-4-(2',6',6'-trimethyl-1'-cyclohexen-1'-yl)-3-butenal (2) was only moderate (20%), and (9R,10S)-13-cis-11,12-didehydro-9,10-dihydro-10-hydroxyretinol (3b) predominated. The LiAlH(4) reduction of the C triple bond C bond in the diastereoisomeric diols 3 afforded 13-cis-9,10-dihydro-10-hydroxyretinols 4a and 4b as major products together with 11-cis-13-cis-isomers and the deoxygenated compound (3EZ,5EZ,8E)-3,7-dimethyl-9-(2,6,6-trimethyl-1-cyclohexen-1-yl)-1,3,5,8-nonatetraene (9). Reaction of 15-acetates of the pure diastereoisomeric allylic alcohols 4a and 4b with PBr(3) occurred with significant but not identical retention of configuration, and with concomitant formation of the rearranged bromide 11.     

Synthesis of chiral nonionic superbases based on iminophosphoranes

Optically active azides derived from penta‐O‐acetylglycose tartaric acid and quinine when reacted with the proazaphosphatrane P(MeNCH₂‐CH₂)₃N gave highly basic iminophosphoranes that are potential asymmetric catalysts and ligands for a variety of reactions. Preliminary results show that the enantiomers are formed in unequal proportions. © 2000 John Wiley & Sons, Inc. Heteroatom Chem 11:251‐253, 2000     

Organocatalysed asymmetric Mannich reactions

The asymmetric Mannich reaction ranks among the most potent enantioselective and diastereoselective C-C-bond forming reactions. In recent years, organocatalysed versions of asymmetric Mannich processes have been increasingly reported and used in a rapidly growing number of applications. This tutorial review provides an overview of the recent history of the asymmetric organocatalysed Mannich reaction, including scope and limitations, and application of different catalyst systems.     

Ligand-, copper-, and amine-free sonogashira reaction of aryl iodides and bromides with terminal alkynes

Conditions for an efficient ligand-, copper-, and amine-free palladium-catalyzed Sonogashira reaction of aryl iodides and bromides with terminal alkynes have been developed. Critical to the success of this new protocol is the use of tetrabutylammonium acetate as the base. Noteworthy features of this method are room-temperature conditions and the tolerance of a broad range of functional groups in both reaction partners.     

P(MeNCH2CH2)3N: a highly selective reagent for synthesizing trans-epoxides from aryl aldehydes

In contrast to its acyclic analogue P(NMe2)3 (1), which in benzene at room temperature reacts with two aryl aldehyde molecules bearing electron-withdrawing groups to give the corresponding diaryl epoxide as an isomeric mixture (trans/cis ratios: 72/28-51/49), P(MeNCH2CH2)3N (2a) under the same reaction conditions is found to be a highly selective reagent that provides epoxides with trans/cis ratios as high as 99/1. These reactions are faster with 2a, because its phosphorus atom is apparently more nucleophilic than that in 1. Thus, it is found that 2a more easily forms 1:1 and 1:2 adducts with one or two molecules of aldehyde, respectively. These adducts apparently are intermediates in the formation of the product epoxide and the corresponding phosphine oxides of 1 and 2a.