Merrifield Resin-C6H4CH2N3P(MeNCH2CH2)3N: an efficient reusable catalyst for room-temperature 1,4-addition reactions and a more convenient synthesis of its precursor P(MeNCH2CH2)3N

1,4-additions to a variety of Michael acceptors with a wide variety of donors were efficiently catalyzed at room temperature by the title reusable Merrifield resin-supported catalyst. Advantages of this catalyst include a simple workup (filtration of the reaction mixture) and good to excellent product yields. We also report a substantially simplified synthesis of the commercially available strong nonionic base 1, a precursor to the title polymer-bound catalyst.     

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.     

P(i-BuNCH2CH2)3N: an efficient promoter for the nucleophilic aromatic substitution reaction of aryl fluorides with aryl TBDMS (or TMS) ethers

[reaction: see text]. The nucleophilic aromatic substitution reaction between electron-deficient aryl fluorides and aryl TBDMS (or TMS) ethers has been shown to be efficiently promoted by proazaphosphatranes such as P(i-BuNCH(2)CH(2))(3)N (3). Excellent yields of diaryl ether products were obtained under unusually mild conditions.     

PhCH=P[MeNCH(2)CH(2)](3)N: a novel ylide for quantitative E selectivity in the Wittig reaction

PhCH=P[MeNCH(2)CH(2)](3)N (1), a semi-stabilized ylide prepared from the commercially available nonionic base P[MeNCH(2)CH(2)](3)N, reacts with aldehydes to give alkenes in high yield with quantitative E selectivity. In contrast with other ylides, this E selectivity is maintained despite changes in the metal ion of the ionic base used to deprotonate 1, temperature, and solvent polarity. In conjunction with structural parameters gained from the X-ray molecular structure of 1, the pathway to E selectivity in these reactions is rationalized by the Vedejs model of Wittig reaction stereochemistry.     

P(RNCH(2)CH(2))(3)N: efficient 1,4-addition catalysts

The 1,4-addition of primary alcohols, higher nitroalkanes, and a Schiff's base of an alpha-amino ester to alpha,beta-unsaturated substrates produces the corresponding products in moderate to excellent yields when carried out at -63 to 70 degrees C in the presence of catalytic amounts of the nonionic strong bases P(RNCH(2)CH(2))(3)N (R = Me, i-Pr, i-Bu) in isobutyronitrile. Diastereoselectivity for the anti form of the product is high in the case of the Schiff's base in the absence of lithium ion. These catalysts are easily removed from the product by either column filtration through silica gel or via aqueous workup.     

P(i-BuNCH2CH2)3N: an efficient ligand for the direct alpha-arylation of nitriles with aryl bromides

A new catalyst system for the synthesis of alpha-aryl-substituted nitriles is reported. The bicyclic triaminophosphine P(i-BuNCH(2)CH(2))(3)N (1b) serves as an efficient and versatile ligand for the palladium-catalyzed direct alpha-arylation of nitriles with aryl bromides. Using ligand 1b, ethyl cyanoacetate and primary as well as secondary nitriles are efficiently coupled with a wide variety of aryl bromides possessing electron-rich, electron-poor, electron-neutral, and sterically hindered groups.     

Reactions of P(MeNCH2CH2)3N with primary,secondary, and tertiary alkyl halides: Evidence for a solvent-enhanced dehydrohalogenation

The reactions of P(MeNCH₂CH₂)₃N, 1, with Mel, EtI, EtBr, n-PrBr, n-BuI, i-PrBr, PhCH₂CHBrCH₃, MeCHBr(CH₂)₄Me, s-BuBr, and t-BuBr were studied. The reactions of the primary alkyl halides produced the corresponding phosphonium cationic compounds, whereas the secondary and tertiary halides underwent elimination to form the corresponding olefins and the protonated form of 1. Based on ¹H and ¹³C NMR studies, it appears that elimination is exclusively trans, favoring the Saytzeff product. It was also observed that this reaction is enhanced by the solvent CH₃CN. The X-ray crystal structure of [Me(I)] I is also reported, featuring a transannular distance of 2.773 Å (2) facilitated by a rather wide average equatorial MeN-P-NMe bond angle of 113.1 (2)°. © 1996 John Wiley & Sons, Inc.     

Tetrabutylammonium tribromide (TBATB)-MeOH: An efficient chemoselective reagent for the cleavage of tert-butyldimethylsilyl (TBDMS) ethers

TBDMS, THP, and DMT ethers are efficiently deprotected with tetrabutylammonium tribromide in methanol. The apparent order of stability of different protecting group is phenolic TBDMS > 1 degrees OTBDPS > 2 degrees OTBDMS > 2 degrees OTHP > 1 degrees OTHP > 1 degrees OTBDMS > 1 degrees ODMT. TBDMS ether has been cleaved selectively in the presence of isopropylidine, Bn, Ac, Bz, THP, and TBDPS groups. This method is high yielding, fast, clean, safe, cost-effective, and therefore most suitable for practical organic synthesis.     

P[N(i-Bu)CH2CH2]3N: a versatile ligand for the Pd-catalyzed amination of aryl chlorides

[reaction: see text] Palladium-catalyzed amination reactions of aryl chlorides with amines proceeded in the presence of the bicyclic triaminophosphine P[N(i-Bu)CH(2)CH(2)](3)N to afford the corresponding arylamines in good to excellent yields. Electron-poor, electron-neutral, and electron-rich aryl chlorides all participated with equal ease.     

P(RNCH2CH2)3N: catalysts for the head-to-tail dimerization of methyl acrylate

The dimerization of methyl acrylate to the head-to-tail 2-methylene-pentanedioic acid dimethyl ester product was realized in 82 and 85% yield in only 4 h at room temperature in THF in the presence of catalytic amounts of P(RNCH2CH2)3N (R = i-Bu and Bn, respectively). These phosphines are to our knowledge the best nonmetallic catalysts so far reported for this reaction. In contrast, less sterically hindered P(MeNCH2CH2)3N failed to catalyze this dimerization, giving oligomer or polymer instead.     

New superhindered polydentate polyphosphine ligands P(CH2CH2P(t)Bu2)3, PhP(CH2CH2P(t)Bu2)2, P(CH2CH2CH2P(t)Bu2)3, and their ruthenium(II) chloride complexes

The synthesis and characterization of the extremely hindered phosphine ligands, P(CH(2)CH(2)P(t)Bu(2))(3) (P(2)P(3)(tBu), 1), PhP(CH(2)CH(2)P(t)Bu(2))(2) (PhP(2)P(2)(tBu), 2), and P(CH(2)CH(2)CH(2)P(t)Bu(2))(3) (P(3)P(3)(tBu), 3) are reported, along with the synthesis and characterization of ruthenium chloro complexes RuCl(2)(P(2)P(3)(tBu)) (4), RuCl(2)(PhP(2)P(2)(tBu)) (5), and RuCl(2)(P(3)P(3)(tBu)) (6). The bulky P(2)P(3)(tBu) (1) and P(3)P(3)(tBu) (3) ligands are the most sterically encumbered PP(3)-type ligands so far synthesized, and in all cases, only three phosphorus donors are able to bind to the metal center. Complexes RuCl(2)(PhP(2)P(2)(tBu)) (5) and RuCl(2)(P(3)P(3)(tBu)) (6) were characterized by crystallography. Low temperature solution and solid state (31)P{(1)H} NMR were used to demonstrate that the structure of RuCl(2)(P(2)P(3)(tBu)) (4) is probably analogous to that of RuCl(2)(PhP(2)P(2)(tBu)) (5) which had been structurally characterized.     

An efficient and chemoselective deprotection of tert-butyldimethylsilyl (TBDMS) ethers using tailor-made ionic liquid

Phenolic tert-butyldimethylsilyl (TBDMS) ethers can be deprotected to yield phenols in excellent yield using tailor-made ionic liquid [dihexaEGim][OMs] (dihexaEGim = dihexaethylene glycolic imidazolium salt) as an organic catalyst with alkali-metal fluoride in tert-amyl alcohol. On the contrary, all TBDMS protecting groups can be cleaved cleanly from the bis-TBDMS ether using the same reaction in CH₃CN solvent instead of tert-alcohol at 100 °C. This [dihexaEGim][OMs]/tert-amyl alcohol media system allows the highly selective phenolic deprotection reaction of various bis-TBDMS ethers containing both phenolic and aliphatic TBDMS ethers to provide the corresponding phenols in high yield.     

A Tri-Coordinate-Magnesium Silylamide Complex: {[(CH3)3Si]2N}2MgO(CH2CH2)2OMg{N[Si(CH3)3]2}2

The reaction of diethylmagnesium dioxane adduct solution with 1,1,1,3,3,3-hexamethyldisilazan ((CH₃)₃SiNHSi(CH₃)₃) gives {[(CH₃)₃Si]₂N}₂MgO(CH₂CH₂)₂OMg{N[Si(CH₃)₃]₂}₂ (1); this alkoxomagnesium silylamide in the solid state contains unprecedented three-coordinate magnesium and oxygen atoms.     

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.