Copper-catalyzed regioselective allylic substitution reactions with indium organometallics

The first nucleophilic allylic substitution reactions of triorganoindium compounds with allylic halides and phosphates are reported. The reactions of trialkyl- and triarylindium reagents with cinnamyl and geranyl halides and phosphates, with the aid of copper catalysis [Cu(OTf)(2)/P(OEt)(3)], are described. In general, the reaction proceeds efficiently to give good yields and regioselectively to afford the S(N)2' product.     

Regio- and enantioselective control in the reactions of alpha-(N-carbamoyl)alkylcuprates with allylic phosphates

Alpha-(N-carbamoyl)alkylcuprates (RCuCNLi or R2CuLi) react with allylic phosphates to afford homoallylic amines in good chemical yields. Regioselectivity is governed by steric factors in both the cuprate reagent and phosphate substrate and systems can be designed to give either the S(N)2' or S(N)2 substitution product cleanly. Excellent enantioselectivities can be achieved with either a scalemic alpha-di[(N-carbamoyl)alkyl]cuprate and an achiral phosphate or with a scalemic allylic phosphate and an achiral cuprate reagent. [reaction: see text]     

Reaction of alpha-(N-carbamoyl)alkylcuprates with enantioenriched propargyl electrophiles: synthesis of enantioenriched 3-pyrrolines

Enantioenriched propargyl mesylates or perfluorobenzoates react with alpha-(N-carbamoyl)alkylcuprates to afford scalemic alpha-(N-carbamoyl) allenes which undergo N-Boc deprotection and AgNO3-promoted cyclization to afford N-alkyl-3-pyrrolines. The synthetic sequence proceeds under optimal conditions with no loss of enantiopurity relative to the starting propargyl alcohols prepared by asymmetric addition of terminal alkynes to aldehydes.     

An "anti-Baldwin" 3-exo-dig cyclization: preparation of vinylidene cyclopropanes from electron-poor alkenes

Stabilized carbanions undergo an uncommon 3-exodig cyclization onto propargyl halides through an SN2' substitution. Propargyl iodides as electrophiles are necessary to achieve good yields (36-95%) for most substrates, although the usefulness of chlorides and bromides is documented. A variety of monocyclic and bicyclic vinylidene cyclopropanes can be prepared. These products are not available by standard carbene methodology.     

Palladium-catalyzed cross-coupling reaction of triorganoindium reagents with propargylic esters

[reaction: see text] Triorganoindium reagents (R(3)In) react with propargylic esters under palladium catalysis via an S(N)2' rearrangement to afford allenes in good yields and with high regioselectivity. The reaction proceeds smoothly at room temperature with a variety of R(3)In (aryl, alkenyl, alkynyl, and methyl). When chiral, nonracemic propargylic esters are employed, the reaction takes place with high anti-stereoselectivity providing allenes with high enantiomeric excess.     

Enantioselective reactions of scalemic acyclic alpha-(alkoxy)alkyl- and alpha-(N-carbamoyl)alkylcuprates

[reaction: see text] Scalemic acyclic alpha-(alkoxy)alkyl- and alpha-(N-carbamoyl)alkylcuprates prepared from organostannanes via organolithium reagents react with vinyl iodides, propargyl mesylates, and alpha,beta-enones to afford coupled products with enantioselectivities ranging from 0 to 99% ee depending upon cuprate reagent, substrate structure, solvent, and temperature. In general, lithium cuprates give higher chemical yields and lower enantioselectivities, while the trends are reversed for the corresponding zinc cuprate reagents.     

Synthesis of nitrogen-containing heterocycles 6. Formation and structures of imidazolinones and related compounds through cyclization of diaminomethylenehydrazones with dimethyl acetylenedicarboxylate

Diaminomethylenehydrazones 1 of aromatic and aliphatic carbonyl compounds react with dimethyl acetylenedicarboxylate (DMAD) at room temperature to give four types of heterocycles, (5-oxoimidazolin-4-ylidene) acetates 2, 3 and 6 , (2-imino-5-oxoimidazolidin-4-ylidene) acetate 4 and 6-oxo-1,6-dihydropyrimidine-4-carboxylates 5 according to the substitution patterns of 1 in moderate to high yields. Amino (N,N-dimethylamino)methylenehydrazones of ketones give exclusively (5-oxoimidazolin-4-yl-idene) acetates, both (Z)- and (E)-isomers 2 and 3 about the exocyclic alkenic linkage, with the (Z)-isomer 2 generally being predominant, while those of aldehydes give 5 . Diamino- and amino (N-methylamino)methylenehydrazones produce 5 and/or 6 and di (N-methylamino) methylenehydrazone gives (2-imino-5-oxoimidazolidin-4-ylidene) acetate 4 as the sole cyclized product.     

Reactivity and enantioselectivity in the reactions of scalemic stereogenic alpha-(N-carbamoyl)alkylcuprates

Stereogenic 2-(N-carbamoyl)pyrrolidinylcuprates prepared from scalemic (i.e., enantioenriched) N-Boc-2-lithiopyrrolidine and THF soluble CuCN.2LiCl react with vinyl iodides, vinyl triflates, beta-iodo-alpha,beta-enoates, propargyl mesylates, and allyl bromide to afford the substitution products with excellent enantioselectivity. Excellent enantiomeric ratios are obtained in the conjugate addition reactions with methyl vinyl ketone while low enantiomeric ratios can be achieved with acrylate esters using HMPA/TMSCl activation. Enantiomeric ratios vary with substrate substitution patterns and the observed enantioselectivities appear to be more a function of cuprate-electrophile reactivities than of the reaction type (e.g., substitution, conjugate addition). Low enantiomeric ratios are obtained with the alpha-(N-carbamoyl)benzylcuprates. The lithium-copper transmetalation and cuprate vinylation reactions proceed with retention of configuration.     

Preparation of C2-symmetric allenes by palladium-catalyzed double-nucleophilic substitution on 3-bromopenta-2,4-dienyl acetate

Easily accessible 3-bromopenta-2,4-dienyl acetate was applied to the palladium-catalyzed reaction with soft nucleophiles. The reaction proceeded through the stepwise 2-fold nucleophilic substitution via formal S(N)2' and S(N)2 processes giving the various doubly functionalized C(2)-symmetric allenes in good yields.     

Palladium-catalyzed three-component assembling of allenes, organic halides, and arylboronic acids.

An efficient method for the construction of two carbon-carbon bonds in a regio- and stereoselective fashion via palladium-catalyzed assembling of allenes, organic halides, and arylboronic acids is described. Organic halides (RI = C(6)H(5)I, o-, m-, and p-CH(3)OC(6)H(4)I, p-C(2)H(5)OCOC(6)H(4)I, p-CH(3)COC(6)H(4)I, p-CH(3)C(6)H(4)I, p-CH(3)C(6)H(4)Br, p-CH(3)C(6)H(4)Cl, p-NO(2)C(6)H(4)I, p-NO(2)C(6)H(4)Br, p-NO(2)C(6)H(4)Cl, p-IC(6)H(4)Cl, 1-iodonaphthalene, 2-iodothiophene, 3-iodo-2-cyclopenten-1-one, 3-iodo-5,5-dimethyl-2-cyclohexen-1-one, C(6)Eta(5)(Br)C=CH(2) and ICH(2)CO(2)C(2)H(5)), and arylboronic acids (ArB(OH)(2), Ar = C(6)H(5), p-CH(3)OC(6)H(4), m-NO(2)C(6)H(4), p-FC(6)H(4), 1-C(10)H(7), and o-, m-, and p-CHOC(6)H(4)) undergo Suzuki-type three-component assembling with 1,1-dimethylallene to give the corresponding allylic derivatives, (CH(3))(2)=CRCH(2)Ar, in DMF at 70 degrees C in the presence of CsF using Pd(dba)(2) as the catalyst. Higher yields of products were obtained for aryl iodides than for the corresponding aryl bromides and chlorides. This three-component assembling is highly regioselective, with the organic group on halides adding to the middle carbon and the aryl group on arylboronic acids to the unsubstituted terminal carbon of allenes. Monosubstituted allenes 1b-e (cyclopentylallene, cyclohexylallene, tert-butylallene, and n-butylallene) also undergo similar assembling reaction with organic halides and arylboronic acids to afford the corresponding products 7a-i with high regio- and stereoselectivity. Based on the known palladium chemistry, a mechanism is proposed to account for the catalytic reaction and the stereochemistry.     

Synthesis of polyfunctional allenes by successive copper-mediated substitutions

Readily available 1,1-dichloro-2-alkynes are versatile starting materials for the synthesis of polyfunctionalized allenes. They can be prepared from commercially available terminal alkynes in a two-step procedure. The Cu-mediated reaction of several 1,1-propargylic derivatives with functionalized alkyl, benzylic, or allylic zinc reagents proceeds exclusively with S(N)2' selectivity and allows a rapid and efficient synthesis of functionalized chloroallenes. These chloroallenes undergo a novel Cu(I) -catalyzed substitution reaction with functionalized arylmagnesium reagents with excellent S(N)2 selectivity to give trisubstituted polyfunctionalized allenes. The functional group tolerance is excellent and functionalities, such as cyano, keto, ester, phosphate, trifluoromethyl, and halogens, are well tolerated.     

Palladium-catalysed synthesis of allyl acetates from allenes

Allyl acetates were synthesised from allenes utilising methodology based on the general reactivity of π-allyl palladium intermediates which participate efficiently in transformations involving nucleophiles. Reactions of allenes and aryl iodides in the presence of AcONa and Pd(OAc)₂/PPh₃ as the catalytic system afforded allyl acetates in moderate to good yields. Monosubstituted allenes, depending on their structure, produced either a separable mixture of two regioisomeric products or a single regioisomer. As allylic acetates can be easily hydrolysed, the methodology is applicable for the synthesis of allyl alcohols as well.     

Ni- and Pd-catalyzed synthesis of substituted and functionalized allylic boronates

Two highly efficient and convenient methods for the synthesis of functionalized and substituted allylic boronates are described. In one procedure, readily available allylic acetates are converted to allylic boronates catalyzed by Ni/PCy(3) or Ni/PPh(3) complexes with high levels of stereoselectivity and in good yields. Alternatively, the borylation can be accomplished with commercially available Pd catalysts [e.g., Pd(2)(dba)(3), PdCl(2), Pd/C], starting with easily accessed allylic halides.     

Palladium-catalyzed cross-coupling reactions of allylic halides and acetates with indium organometallics

The palladium(0)-catalyzed cross-coupling reaction of allylic halides and acetates with indium organometallics is reported. In this synthetic transformation, triorganoindium compounds and tetraorganoindates (aryl, alkenyl, and methyl) react with cinnamyl and geranyl halides and acetates to afford the S(N)2 product regioselectively and in good yield. The reaction proceeds with net inversion of the stereochemical configuration.     

Palladium-catalyzed three-component coupling of arynes with allylic acetates or halides and terminal alkynes promoted by cuprous iodide

Benzynes react with allylic acetates or halides and terminal alkynes in the presence of Pd(PPh3)4, CuI and CsF in CH3CN at 50 degrees C for 5 h to give 1-allyl-2-alkynylbenzene derivatives in good to excellent yields.     

Highly regio- and stereoselective acylboration, acylsilation, and acylstannation of allenes catalyzed by phosphine-free palladium complexes: an efficient route to a new class of 2-acylallylmetal reagents

A new method for the synthesis of substituted 2-acylallylmetal reagents in a highly regio- and stereoselective fashion involving a three-component assembly of allenes, acyl chlorides, and bimetallic reagents (B-B, Si-Si, and Sn-Sn) catalyzed by phosphine-free palladium complexes is described. Treatment of various allenes (CR(2)R(3)=C=CH(2)) with acyl chlorides (R(1)COCl) and bispinacolatodiboron in the presence of PdCl(2)(CH(3)CN)(2) in toluene at 80 degrees C gave 2-acylallylboronates in moderate to good yields. The acylsilation of allenes with acid chlorides and hexamethyldisilane (5) proceeded successfully in the presence of Pd(dba)(2) in CH(3)CN affording the corresponding allylsilanes (CR(2)R(3)=C(COR(1))CH(2)SiMe(3)) in good to moderate yields. Several chloroformates (R(4)OCOCl) also react with 1,1-dimethylallene (2a) and 5 to afford allylsilanes (CR(2)R(3)=C(COOR(4))CH(2)SiMe(3)) in 66-70% yields. Acylstannation of allenes could also be achieved by slow addition of hexabutylditin (10) to the reaction mixture of acyl chloride (or chloroformate) and allene 2a in CH(3)CN in the presence of Pd(dba)(2) at 60 degrees C; the corresponding 2-substituted allylstannanes were isolated in moderate to good yields. The above catalytic reactions are completely regioselective and highly stereoselective. A mechanism is proposed to account for the catalytic reactions and the stereochemistry.     

Highly regio- and chemoselective [2 + 2 + 2] cycloaddition of electron-deficient diynes with allenes catalyzed by nickel complexes: a novel entry to polysubstituted benzene derivatives

Diynes 1a-c [X(CH(2)Ctbd1;CCO(2)Me)(2): X = (CH(2))(2), 1a, X = CH(2), 1b and X = O, 1c] undergo [2 + 2 + 2] ene-diyne cycloaddition reactions with a variety of allenes (n-butylallene 2a, phenylallene 2b, (4-chlorophenyl)allene 2c, (4-bromophenyl)allene 2d, (3-methoxyphenyl)allene 2e, 1-naphthylallene 2f, cyclohexylallene 2g and cyclopentylallene 2h) in the presence of Ni(dppe)Br(2) and Zn powder in CH(3)CN at 80 degrees C for 8 h to give the corresponding polysubstituted benzene derivatives 4a-l in good to excellent yields. Under similar reaction conditions, unsymmetrical diynes 5a-c (HCtbd1;CCH(2)XCH(2)Ctbd1;CCO(2)Me) react with allenes 2 to afford exclusively the corresponding meta-isomers 6a-g in 73-86% yields. The catalytic reaction is highly regioselective and completely chemoselective. This synthetic method is compatible with many functional groups such as Cl, Br, and OMe on the phenyl group of the allene moiety and an ether linkage in a diyne moiety. In this catalytic reaction, allenes are synthetically equivalent to terminal alkynes. Interestingly, unsymmetrical diyne 7 (MeCtbd1;C(CH(2))(4)Ctbd1;CCO(2)Me) undergoes 2:1 cocyclotrimerization with allenes 2a and 2g to afford the corresponding polysubstituted benzene derivatives 9a,b in 87% and 82% yields, respectively. A plausible mechanism involving a nickelacycloheptadiene intermediate is proposed to account for this nickel-catalyzed reaction.     

Halogen- and N-haloimide-promoted homo- and heterocoupling of alpha-(N-carbamoyl)alkylcuprates and alpha-(alkoxy)alkylcuprates

Both homo- and mixed lithium di-alpha-(heteroatom)alkylcuprates readily dimerize upon addition of halogens (e.g., I(2), Br(2)) or N-halosuccinimides to afford the coupled products in excellent yields. Higher yields result when the requisite alpha-(heteroatom)alkyllithium reagents are generated via deprotonation rather than by transmetalation of the corresponding stannanes. Mixed lithium dialkyl- or alkyl(aryl)cuprate reagents containing one alpha-(heteroatom)alkyl ligand and one simple alkyl or aryl ligand give significantly lower yields of coupled product. Low enantioselectivity has been achieved in the oxidative coupling of lithium (n-Bu)(2-pyrrolidinyl)cuprate.     

Carbonylative cross-coupling reaction of ethynylstibane with aryl iodides

Palladium-catalyzed carbonylative cross-coupling reaction of ethynylstibane (PhSbPh(2)) and aryl iodides (Ar-I) is described. The reaction of the stibanes and the halides under 1 atm of carbon monoxide in N,N-dimethylacetamide using a combination of 5 mol% Pd(OAc)(2) and 4 equivalents (20 mol%) of PPh(3) brought about carbonylative cross-coupling reaction to afford arylethynylketones [ArC(O)Ph] in good yields along with a small amount of directly coupled products, aryl acetylens (ArPh). Formation of the side product was completely suppressed by conducting the reaction under high CO pressure (20 atm) conditions. The present method provides a variety of carbonylated products in good yield even with electron-deficient aryl iodides which usually give inferior results due to their tendency to undergo decarbonylation in the cross-coupling reaction of ethynylstibanes and acyl halides.     

Studies toward the synthesis of alpha-fluorinated phosphonates via tin-mediated cleavage of alpha-fluoro-alpha-(pyrimidin-2-ylsulfonyl)alkylphosphonates. Intramolecular cyclization of the alpha-phosphonyl radicals

Treatment of the alpha carbanions generated from several alpha-(pyrimidin-2-ylsulfonyl)alkylphosphonates with Selectfluor gave high yields of the alpha-fluoro-alpha-(pyrimidin-2-ylsulfonyl)alkylphoshonates, which were desulfonylated [Bu(3)SnH/2,2'-azobisisobutyronitrile (AIBN)/benzene or toluene/Delta] to give alpha-fluoroalkylphosphonates. "Catalytic" tin hydride, generated from tributyltin chloride and excess polymethylhydrosiloxane in the presence of potassium fluoride, also effected removal of the pi-deficient alpha-(pyrimidin-2-ylsulfonyl) group from the phosphonate esters. Substitution of Bu(3)SnD for Bu(3)SnH gave access to alpha-deuterium-labeled phosphonates. Prolonged treatment of alpha-(pyridin-2-ylsulfonyl)alkylphosphonate with excess Bu(3)SnH/AIBN or catalytic tin hydride also effected desulfonylation but in moderate yields. This represents a mild new methodology for removal of the synthetically useful pi-deficient heterocyclic sulfone moiety and an alternative route for the preparation of alpha-fluorinated phosphonates. Desulfonylation is suggested to proceed via attack of tin radical at an oxygen (or sulfur) atom of the sulfonyl group to give a stabilized alpha-phosphonyl radical intermediate. The latter was found to undergo 5-exo-trig ring closure to give the corresponding 2-methylcyclopentylphosphonates. Treatment of diethyl 1-bromohex-6-enylphosphonate with Bu(3)SnH/AIBN produced an analogous mixture of ring-closure products. Treatment of [(2-bromo-5- methoxyphenyl)(fluoro)(pyrimidin-2-ylsulfonyl)]methylphosphonate with Bu(3)SnH resulted in an intramolecular radical [1,5]-ipso substitution reaction and migration of the pyrimidinyl ring to give fluoro[5-methoxy-2-(pyrimidin-2-yl)phenyl]methylphosphonate.