N-Boc-L-valine-connected amidomonophosphane rhodium(I) catalyst for asymmetric arylation of N-tosylarylimines with arylboroxines

A catalytic asymmetric arylation of sterically tuned imines with arylboroxines was developed by using N-Boc-l-valine-connected amidomonophosphane rhodium(I) catalyst in n-PrOH. The TMS group used for the steric tuning of imines is convertible to other functionalities that are applicable as a key foothold for the carbon-carbon bond-forming coupling reactions.     

Rhodium-catalysed cyclisation reaction of allenynes with arylboronic acids

Allenynes having malonate-based tethers reacted with arylboronic acids in the presence of a rhodium(I) catalyst to sequentially form three carbon-carbon bonds, and arylated bicyclic skeletons were constructed in a stereoselective manner.     

Transition-metal-free electrophilic amination of arylboroxines

A transition-metal-free strategy to construct C(sp(2))-N bonds using arylboroxines and O-benzoyl hydroxylamines as coupling partners has been developed. This transformation provides a useful method to access various aromatic amines.     

Rhodium-catalysed ortho-alkynylation of nitroarenes

The ortho-alkynylation of nitro-(hetero)arenes takes place in the presence of a Rh(iii) catalyst to deliver a wide variety of alkynylated nitroarenes regioselectively. These interesting products could be further derivatized by selective reduction of the nitro group or palladium-catalysed couplings. Experimental and computational mechanistic studies demonstrate that the reaction proceeds via a turnover-limiting electrophilic C–H metalation ortho to the strongly electron-withdrawing nitro group.

Rh(iii)-catalyzed ortho-alkynylation of nitro-(hetero)arenes leads to a wide variety of alkynylated nitroarenes via a turnover-limiting electrophilic C–H ortho-metalation.     

Nickel-catalyzed 1,2-addition of arylboroxines to aromatic aldehydes

Development of Ni-Et-Duphos-catalyzed 1,2-addition of arylboroxines to aromatic aldehydes is described. The dramatic effect of boron reagent and phosphine ligand is observed. This method with a phosphine ligand allows asymmetric arylation of aromatic aldehydes (up to 78% ee).     

Noncatalytic substitutive O-acylation of oxiranes with trifluoroacetic anhydride

1-R-3-Methyl-2,3-epoxybutanes have been found to react with trifluoroacetic anhydride at 20–40C in the absence of a catalyst to give mixtures of the difluoroacetate and the product of substitutive O-acylation. The formation of the latter is favored by raising the temperature. The reaction mechanism is discussed.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 2, pp. 174–176, February, 1990.     

Meerwein arylation with 3-fluorobutenone

3-Fluorobutenone (7) reacts with aryl triazenes in the presence of zinc iodide to give 4-aryl-3-fluoro-3-iodo-2-butanones (9a-9f) in moderate yields. The products arise from a free radical process that terminated by iodination of an alkyl radical. The process yields unusual geminal iodo-fluoro compounds.     

Rhodium-catalysed addition of arylboronic acids to oxabenzonorbornadienes

The facile addition reaction of boronic acids to oxabenzonorbornadienes was achieved using a catalytic amount of a rhodium(I) complex having P(OEt)3 ligands, affording cis-2-aryl-1,2-dihydro-1-naphthol stereoselectively, and in good yield without concomitant deboronation of the boronic acid.     

Rhodium-catalysed enantioselective synthesis of 4-arylchroman-2-ones

The rhodium-catalysed enantioselective 1,4-addition of organoboron reagents to arylidene Meldrum's acids as acceptors, allows convenient access to 4-arylchroman-2-ones with good to excellent levels of enantioselectivity. The use of silyl-protected dioxaborinanes as donors was found to be advantageous to achieving good yields of product under anhydrous conditions.     

Titanyl complexes with 1,10-phenanthroline-based diols

The reaction of the O,N,N,O-type ligands, namely, 4,7-bis(4-tert-butylphenoxy)₂-2,9-(HOCRR’CH)₂-1,10-phenanthrolines, LH₂ (R = R′ = Ph (1), RR′ = ?(CH₂)₅? (2), 2,2-adamantylene (3)), with an equimolar amount of Ti(OPrⁱ)₄ in toluene under mild conditions afforded the mixtures of the corresponding titanium LTi(OPrⁱ)₂(4–6) and titanyl complexes LTi=O (7–9). Subsequent reflux of these mixtures in toluene gave pure derivatives 7–9, which were characterized by ¹H and ¹³C NMR spectroscopy and elemental analysis. The presence of the Ti=O fragment in molecules 7–9 was unambiguously confirmed by IR spectroscopy data and was found to be consistent with the data of quantum chemical calculations. The new ligand 3 was obtained by sequential treatment of 4,7-di(4-tert-butylphenoxy)-2,9-dimethyl-1,10-phenanthroline with an excess of lithium diisopropylamide and adamantan-2-one. The titanyl complex 7 was found to be moderately active as an initiator of ε-caprolactone polymerization.

     

Rhodium-catalysed addition of organotrialkoxysilanes to alpha-substituted acrylic esters

The cationic rhodium complex [Rh(cod)2][BF4] effectively catalyses the 1,4-addition of organotrialkoxysilanes to alpha-substituted acrylic esters. The reactions are promoted by heating in an oil-bath or more conveniently in a microwave reactor allowing rapid access to a useful range of functionalised products including 2-alkyl succinates and alpha-amino acid derivatives.     

Rhodium-catalysed asymmetric hydrosilylation of ketones using HETPHOX ligands

The HETPHOX ligand class was applied to the rhodium-catalysed asymmetric hydrosilylation of a range of substituted acetophenones. Enantioselective hydrosilylation of acetophenone with the tert-butyl substituted HETPHOX ligand gave (R)-phenylethanol in excellent enantioselectivity (84% ee) and in good conversion (80%). When applied to the hydrosilylation of other ketones conversions up to 93% and enantioselectivities up to 88% were observed.     

Copper-catalyzed alkene arylation with diaryliodonium salts

Alkenes and arenes represent two classes of feedstock compounds whose union has fundamental importance to synthetic organic chemistry. We report a new approach to alkene arylation using diaryliodonium salts and Cu catalysis. Using a range of simple alkenes, we have shown that the product outcomes differ significantly from those commonly obtained by the Heck reaction. We have used these insights to develop a number of new tandem and cascade reactions that transform readily available alkenes into complex arylated products that may have broad applications in chemical synthesis.     

Reaction of tin porphyrins with vicinal diols

Reactions of tin porphyrins with vicinal diols were investigated. Treatment of (TTP)Sn(CCPh)(2) or (TTP)Sn(NHtolyl)(2) with pinacol and 2,3-diphenylbutane-2,3-diol afforded diolato complexes (TTP)Sn[OC(Me)(2)C(Me)(2)O] (1) and (TTP)Sn[OC(Ph)(Me)C(Ph)(Me)O] (2), respectively. Both complexes underwent C-C cleavage reactions to give (TTP)Sn(II) and ketones. Reaction of (TTP)Sn(CCPh)(2) with 1 equivalent of o-catechol generated (TTP)Sn(CCPh)(OC(6)H(4)OH) (3), which subsequently transformed into (TTP)Sn(OC(6)H(4)O) (4). With excess catechol, disubstituted (TTP)Sn(OC(6)H(4)OH)(2) (5) was obtained. (TTP)Sn(CCPh)(OCHRCHROH) (R = H, 6; R = Ph, 8) and (TTP)Sn(OCHRCHROH)(2) (R = H, 7; R = Ph, 9) were obtained analogously by treatment of (TTP)Sn(CCPh)(2) with appropriate diols. In the presence of dioxygen, tin porphyrin complexes were found to promote the oxidative cleavage of vicinal diols and the oxidation of alpha-ketols to alpha-diketones. Possible reaction mechanisms involving diolato or enediolato intermediates are discussed. The molecular structure of (TTP)Sn(CCPh)(OC(6)H(4)OH) (3) was determined by X-ray crystallography.     

Modification of PET with sterically hindered diols

Poly(ethylene terephthalate) was modified by incorporating bis(hydroxyethyl) tetrasubstituted terephthalates (methyl, chlorine, and bromine) as a third component in the mole ratios of 2–50% (based on dimethyl terephthalate) which resulted in random copolyesters. The presence of steric hindrance imparted additional chain rigidity to the copolymer structure, as shown by increased glass transition temperature (T_g). The effectiveness of the steric groups for conferring rigidity to the copolymer structure was CH₃ > Cl?Br. The copolyesters which contained halogen substituents showed substantial enhancement in flame retardency compared with PET.     

Chemistry of diphenyltetrafluorophosphazene: Reactions with dilithiated diols

Reaction of gem-diphenyltetrafluorophosphazene, [1,1-(C₆H₅)₂]P₃N₃F₄ (1) with LiO(CH₂)₃OLi resulted in the formation of four products, spiro-{3,3-[O(CH₂)₃O]}[1,1-(C₆H₅)₂]P₃N₃F₂ (2), ansa-{3,5-[O(CH₂)₃O]}[1,1-(C₆H₅)₂P₃N₃F₂] (3), bridged-[1,1-(C₆H₅)₂N₃P₃F₃][O(CH₂)₃O][1,1-(C₆H₅)₂N₃P₃F₃] (4) and dangling-[HO(CH₂)₃O][1,1-(C₆H₅)₂P₃N₃F₃] (5) derivatives of 1, among which compound 5 was found to be the major product. Reaction of 1 with the dilithiated ferrocene derived diol, FcCH₂P(S)(CH₂OLi)₂ resulted in the formation of two isomers of ansa substituted fluorophosphazenes namely endo-[1,1-(C₆H₅)₂]{3,5-[FcCH₂P(S)(CH₂O)₂]}P₃N₃F₂ (6) and exo-[1,1-(C₆H₅)₂]{3,5-[FcCH₂P(S)(CH₂O)₂]}P₃N₃F₂ (7). These were formed along with the spiro isomer [1,1-(C₆H₅)₂]{3,3-[FcCH₂P(S)(CH₂O)₂]}P₃N₃F₂ (8) the dangling derivative [1,1-(C₆H₅)₂P₃N₃F₃][OCH₂(FcCH₂)P(S)CH₂OH] (9) and the bridged compound [1,1-(C₆H₅)₂P₃N₃F₃][OCH₂(FcCH₂)P(S)CH₂O][1,1-(C₆H₅)₂P₃N₃F₃] (10). All compounds were separated by column chromatography and characterized by ¹H, ³¹P{¹H}, ¹⁹F NMR, mass spectra and elemental analysis. The spirocyclic compound 8 was also characterized by X-ray crystallography.     

Copper-mediated direct arylation of benzoazoles with aryl iodides

The direct arylation of 1,3-benzoazole compounds with aryl iodides is effectively promoted by CuI with use of PPh₃ and Na₂CO₃ or K₃PO₄ as ligand and base, respectively, in DMF or DMSO to produce the corresponding 2-arylated products with good yields.     

Palladium-catalyzed arylation of electron-rich heterocycles with aryl chlorides

[reaction: see text] Palladium-catalyzed C-H activation: cheap aryl chlorides can now be used for the arylation of a wide variety of electron-rich heterocycles. The key to the success of this reaction is the use of a bulky, electron-rich phosphine ligand. No copper additives are needed.