Asymmetric 1,4-addition of phenylboronic acid to 2-cyclohexenone catalyzed by Rh(I)/binap complexes

Memory of Chirality Concept in Asymmetric Intermolecular Michael Addition of α-Amino Ester Enolates to Enones and Nitroalkenes

A highly stereoselective asymmetric intermolecular conjugate addition of α-amino ester derivatives to cyclic enones via the memory of chirality (MOC) concept in high yields with excellent diastereo- and enantioselectivity (dr >99:1, up to 99% ee) is reported. The applicability and the generality of the strategy was demonstrated by its further exploration to acyclic α,β-unsaturated ketone and aromatic nitroalkenes, resulting in the formation of δ-keto-α-amino ester derivative and γ-nitro-α-amino ester derivatives, respectively, with excellent ee and dr.

Planar-chiral cyrhetrenes for the rhodium-catalyzed asymmetric 1,4-addition and the hydrogenation of enamides

[reaction: see text] The syntheses of novel cyrhetrenes 7a-c and 8a,b are described. These planar-chiral, mono- and diphosphines have been applied as ligands in the Rh-catalyzed 1,4-addition reaction to activated olefins and in the Rh-catalyzed hydrogenation of enamide 12, giving the corresponding products with up to 97 and 93% ee, respectively.

Enantioselective rhodium enolate protonations. A new methodology for the synthesis of beta2-amino acids

[reaction: see text] Rhodium-catalyzed conjugate addition of an aryl boronic acid to alpha-methylamino acrylates followed by enantioselective protonation of the oxa-pi-allylrhodium intermediate provides access to aryl-substituted beta(2)-amino acids. The impact of the different variables of the reaction on the levels of enantioselectivity has been assessed.

Mechanistic studies on the catalytic cycle of rhodium-catalyzed asymmetric 1,4-addition of aryltitanate reagents to alpha,beta-unsaturated ketones

Addition of lithium aryl(tetraisopropoxy)titanates [ArTi(OPr-i)(4)(-)Li(+)] to alpha,beta-unsaturated ketones proceeded with high enantioselectivity (up to 99% ee) in the presence of an excess amount of chlorotrimethylsilane and a rhodium catalyst (3 mol % Rh), generated from [RhCl(C(2)H(4))(2)](2) and (S)-binap, in tetrahydrofuran at 20 degrees C to give high yields of the corresponding silyl enolates as 1,4-addition products. The presence of chlorotrimethylsilane is essential for the 1,4-addition to take place. (31)P NMR spectroscopic studies revealed that the catalytic cycle consists of three transformations, that is, (i) insertion of an enone into arylrhodium species forming (oxa-pi-allyl)rhodium intermediate, (ii) silylation of the (oxa-pi-allyl)rhodium with chlorotrimethylsilane giving silyl enolate and a chloro-rhodium complex, and (iii) transmetalation of aryl group from aryltitanate to the chloro-rhodium regenerating the aryl-rhodium.

Palladium-catalyzed conjugate addition of organosiloxanes to alpha,beta-unsaturated carbonyl compounds and nitroalkenes

The addition of aryltrialkoxysilanes to alpha,beta-unsaturated carbonyl compounds (ketones, aldehydes) and nitroalkenes in the presence of SbCl(3), TBAF, AcOH, and a catalytic amount of Pd(OAc)(2), in CH(3)CN at 60 degrees C, provides the corresponding conjugate addition products in moderate to good yields. The addition of equimolar amounts of SbCl(3) and TBAF is necessary for this reaction to proceed smoothly. The arylpalladium complex, which is generated by the transmetalation from a putative hypercoordinate silicon compound, is considered to be the catalytically active species.

A new cine-substitution of alkenyl sulfones with aryltitanium reagents catalyzed by rhodium: mechanistic studies and catalytic asymmetric synthesis of allylarenes

The reaction of alkenyl sulfones with aryltitanium triisopropoxide (ArTi(OPr-i )3) in the presence of 3 mol % of [Rh(OH)((S)-binap)]2 in THF at 40 degrees C gave high yield of cine-substitution products. The catalytic cycle was established by deuterium-labeling studies, and it was applied to catalytic asymmetric synthesis of allylarenes which proceeds with over 99% enantioselectivity.

Generation of chiral boron enolates by rhodium-catalyzed asymmetric 1,4-addition of 9-aryl-9-borabicyclo[3.3.1]nonanes (B-Ar-9BBN) to alpha,beta-unsaturated ketones

Asymmetric 1,4-addition of 9-phenyl-9-borabicyclo[3.3.1]nonane (2m) to 2-cyclohexenone (1a) proceeded with high enantioselectivity in toluene at 80 degrees C in the presence of 3 mol % of a rhodium catalyst generated from [Rh(OMe)(cod)]2 and (S)-binap to give a high yield of boron enolate (S)-3am, which is 98% enantiomerically pure. Reaction of the boron enolate 3am with electrophiles, methanol-d, propanal, and allyl bromide, gave the corresponding 2-substituted (3S)-3-phenylcyclohexanones with perfect regio- and diastereoselectivity.

Rhodium-catalyzed asymmetric conjugate additions of boronic acids using monodentate phosphoramidite ligands

Monodentate phosphoramidites have been used for the first time as chiral ligands in the Rh-catalyzed enantioselective conjugate addition of arylboronic acids to enones, unsaturated esters, lactones, and nitro alkenes. High reaction rates and ee's up to 89% have been obtained.

Asymmetric 1,4-addition of organosiloxanes to alpha,beta-unsaturated carbonyl compounds catalyzed by a chiral rhodium complex

Highly enantioselective 1,4-addition of organosiloxanes to alpha,beta-unsaturated carbonyl compounds was found to be catalyzed by a chiral rhodium complex generated from [Rh(cod)(MeCN)(2)]BF(4) and (S)-BINAP. Both (E)- and (Z)-1-alkenyl groups as well as aryl groups can be introduced enantioselectively into the beta-position of a variety of ketones, esters, and amides. [reaction--see text]

Rhodium-catalyzed asymmetric 1,4-addition of aryltitanium reagents generating chiral titanium enolates: isolation as silyl enol ethers

The addition of aryltitanium triisopropoxide (ArTi(OPr-i )3) to alpha,beta-unsaturated ketones proceeded with high enantioselectivity (94-99.8% ee) in the presence of 3 mol % of [Rh(OH)((S )-binap)]2 in THF at 20 degrees C to give high yields of the titanium enolates as 1,4-addition products. The titanium enolates were converted into silyl enol ethers by treatment with chlorotrimethylsilane and lithium isopropoxide.

A new type of catalytic tandem 1,4-addition-aldol reaction which proceeds through an (oxa-pi-allyl)rhodium intermediate

The reaction of 9-aryl-9-borabicyclo[3.3.1]nonanes (B-Ar-9BBN) with alpha,beta-unsaturated ketones and aldehydes in the presence of 3 mol % [Rh(OMe)(cod)](2) in toluene at 20 degrees C for 2 h gave high yields of the tandem 1,4-addition-aldol reaction products with high syn selectivity. The reaction proceeds through the catalytic cycle consisting of 1,4-addition of an organorhodium species to an alpha,beta-unsaturated ketone and the aldol addition of the resulting (oxa-pi-allyl)rhodium intermediate to an aldehyde.

Formal enantioselective Michael addition with umpolung of reactivity

By a sequence comprising asymmetric hydroboration, boron-zinc exchange, and transmetalation with copper, allylations, alkynylations, and allenylations of unsaturated ketals or acetals can be performed with good enantioselectivities (see scheme, (-)-IpcBH2 =(-)-isopinocampheylborane, TMS=Me3 Si). The products correspond to a formal Michael addition with inversion of polarity.

Hemilabile amidomonophosphine ligand-rhodium(I) complex-catalyzed asymmetric 1,4-addition of arylboronic acids to cycloalkenones

The asymmetric 1,4-addition reaction of arylboronic acids with cycloalkenones was catalyzed by 1 mol % of an amidomonophosphine-rhodium(I) catalyst in a 10:1 mixture of 1,4-dioxane and water at 100 degrees C, affording 3-arylcycloalkanones in reasonably high enantioselectivity and high yields. It was revealed by NMR, IR, and X-ray spectroscopies that this bidentate amidomonophosphine behaves as a hemilabile ligand that contains a hard donor site in addition to the soft donor in a molecule. Phosphorus atom strongly bonds to rhodium(I), and the amide carbonyl oxygen is coordinatively labile. The reaction efficacy of phenylboronic acid with cyclopent-2-en-1-one was significantly dependent on the possibility of coordination of the amide carbonyl oxygen to rhodium(I).

Catalytic cycle of rhodium-catalyzed asymmetric 1,4-addition of organoboronic acids. Arylrhodium, oxa-pi-allylrhodium, and hydroxorhodium intermediates

The catalytic cycle of asymmetric 1,4-addition of phenylboronic acid to an alpha,beta-unsaturated ketone catalyzed by a rhodium-binap complex was established by use of RhPh(PPh(3))(binap) as a key intermediate. The reaction proceeds through three intermediates, phenylrhodium, oxa-pi-allylrhodium, and hydroxorhodium complexes, all of which were observed in NMR spectroscopic studies. The transformations between the three intermediates, that is, insertion, hydrolysis, and transmetalation, were also observed. On the basis of the catalytic cycle, a more active chiral catalyst, [Rh(OH)(binap)](2), was found and used successfully for the asymmetric 1,4-addition reactions.

Rhodium-catalyzed asymmetric 1,4-addition of organoboron reagents to 5,6-dihydro-2(1H)-pyridinones. Asymmetric synthesis of 4-aryl-2-piperidinones

Catalytic asymmetric synthesis of 4-aryl-2-piperidinones was realized for the first time by asymmetric 1,4-addition of arylboron reagents to 5,6-dihydro-2(1H)-pyridinones in the presence of a chiral bisphosphine-rhodium catalyst. In the reaction introducing 4-fluorophenyl group, the use of 4-fluorophenylboroxine and 1 equiv (to boron) of water at 40 degrees C gave the highest yield of the arylation product with high enantioselectivity (98% ee). The (R)-4-(4-fluorophenyl)-2-piperidinone obtained here is a key intermediate for the synthesis of (-)-Paroxetine.

Catalyzed Asymmetric Arylation Reactions

Addition and substitution reactions with carbon nucleophiles are fundamental processes in organic synthesis, and the development of general catalytic asymmetric variants thereof is still a major challenge today. In contrast to enantioselective alkyl transfer reactions, the corresponding arylations have not yet reached a high level of maturity. The existing protocols are either of no general applicability or are limited in terms of selectivity. This article summarizes established routes for catalytic asymmetric aryl transfer together with the latest developments in this area. The scope and limitations of this reaction are discussed.