Yasuhiro Yamamoto

Improved method for the synthesis of (E)-cyclic-β-alkoxyacrylates under mild conditions

Abstract The oxidative cyclization–methoxycarbonylation of cyclic- and acyclic-4-yn-1-ols 1 in the presence of Pd(II)/ p- benzoquinone in methanol at 0°C under a carbon monoxide atmosphere (balloon) afforded ( E )-cyclic-β-alkoxyacrylates 2 in good to excellent yields. The present reaction is applicable to the above-mentioned substrates bearing the additional functional groups such as acetate, hydroxyl, ketone, ester, terminal acetylene and the acid-sensitive protecting groups (TBDPS, TBDMS, MOM and THP). A new synthesis of the left part of the cystothiazoles is presented.

Unusual formation of cyclic-orthoesters by Pd(II)-mediated cyclization–carbonylation of propargylic acetates

Abstract The oxidative cyclization–methoxycarbonylation of propargylic acetates 1 in the presence of (CH 3 CN) 2 PdCl 2 / p -benzoquinone in methanol under carbon monoxide atmosphere (balloon) afforded ( E )-cyclic-orthoesters 5 in moderate yields.

Asymmetric cyclization–carbonylation of cyclic-2-methyl-2-propargyl-1,3-diols

Abstract The first example of asymmetric cyclization–carbonylation of cyclic-2-methyl-2-propargyl-1,3-diols 1 catalyzed by palladium(II) with chiral bisoxazolines was investigated. The reaction of 1 in the presence of palladium(II)-chiral ligands/p-benzoquinone in methanol at 0 to −45°C under carbon monoxide atmosphere (balloon) afforded (E)-bicyclic-β-alkoxyacrylates 2 in excellent yields with moderate enantioselectivities.

Reactions of palladium complex of N,N-dimethylbenzylamine with aromatic phosphines bearing the methoxy groups at the 2,6-positions

Reactions of [(C 6 H 4 CH 2 NMe 2 - C 2 , N )PdCl] 2 ( 1 ) with (2,6-dimethoxyphenyl)diphenylphosphine (MDMPP), bis(2,6-dimethoxyphenyl)phenylphosphine (BDMPP), and tris(2,6-dimethoxyphenyl)phosphine (TDMPP) gave the corresponding complexes [(C 6 H 4 CH 2 NMe 2 - C 2 ,N)PdCl(L)] ( 2a : L=MDMPP; 2b : L=BDMMP; 2c : L=TDMPP). Reactions of 2 with NaPF 6 led to replacement of the Cl atom with the methoxy-O atom to form the corresponding complexes [(C 6 H 4 CH 2 NMe 2 - C 2 , N )Pd(L)](PF 6 ) ( 3 ). On treatment of 3 with HCl (aq), protonation occurred at the N atom in 3 to give [(C 6 H 4 CH 2 NHMe 2 - C 2 )PdCl(L)] ( 5 ). Based on X-ray structural analyses of 2c , 3a , 3b , 5a and 5c , complexes ( 2b , 2c , 3b , 3c , 5b and 5c ) bearing BDMPP and TDMPP ligands have square-pyramidal structures with a P–O coordination in the axial position and complexes ( 2a , 3a and 5a ) bearing MDMPP have square planar structures. When a complex bearing triphenylphosphine [(C 6 H 4 CH 2 NMe 2 - C 2 , N )PdCl(PPh 3 )] was treated with NaPF 6 , [(C 6 H 4 CH 2 NMe 2 - C 2 , N )Pd(PPh 3 )(O 2 H)](PF 6 ) ( 4 ) bearing a H 2 O ligand was obtained. The reaction with HCl (aq) led to a cleavage of a Pd–C bond to give [PdCl 3 (PPh 3 )][PhCH 2 NHMe 2 ] ( 6 ). X-ray analyses of 4 and 6 were also carried out. Reactions of 1 or 2a with mesityl isocyanide (MesNC) proceeded with replacement of a Cl atom with isocyanide and insertion of isocyanide to produce [(C 6 H 4 CH 2 NMe 2 - C 2 , N )PdCl(MesNC)] ( 7 ) and [C 6 H 4 CH 2 NMe 2 - C 2 )PdCl(MesNC) 2 ] ( 8 ).

New total synthesis of (+)-cystothiazole A

Palladium-catalyzed cyclization–methoxycarbonylation of (2R,3S)-3-methylpenta-4-yne-1,2-diol (7) derived from (2R,3S)-epoxy butanoate 8 followed by methylation gave the tetrahydro-2-furylidene acetate (−)-9, which was converted to the left-half aldehyde (+)-4. A Wittig reaction between (+)-4 and the phosphoranylide derived from the bithiazole-type phosphonium iodide 5 using lithium bis(trimethylsilyl)amide afforded the (+)-cystothiazole A (2).

Palladium(II)-mediated cyclization-carbonylation of 4-yn-1-ones: facile access to 2-cyclopentenone carboxylates

Abstract The oxidative cyclization–carbonylation of 4-yn-1-ones 6 in the presence of (CH 3 CN) 2 PdCl 2 / p -benzoquinone in methanol under a carbon monoxide atmosphere (balloon) afforded cyclic-ketals 7 in good to moderate yields. The product 7 were easily converted into 2-cyclopentenone carboxylates 11 and 12 .

Asymmetric cyclization–carbonylation of 2-propargyl-1,3-dione

Abstract The first example of asymmetric cyclization–carbonylation of 2-propargyl-1,3-dione 1 catalyzed by palladium(II) with chiral bisoxazolines (C.H.-BOX) was investigated. The use of bulky alcohols increased the ee of the products 2 . The product 2d was converted into bicyclic enones 7 and 8 , a useful intermediate for the synthesis of natural products.

Preparations and structures of (η6-arene)ruthenium(II) complexes bearing 1,1′-bis(diphenylphosphinomethyl)ferrocene or 1,1′-bis(diphenylphosphino)ferrocene

Abstract Reactions of bis[dichloro(η6-arene)ruthenium] 1 with 1,1′-bis[(diphenylphosphino)methyl]ferrocene (dpmf) gave the dpmf-P,P′ bridged complexes [(η6-arene)RuCl2]2(μ-dpmf) 2, where arenes=(a) 1,2,3,4-Me4C6H2; (b) C6Me6; (c) p-cymene; (d) 1,2,3,5-Me4C6H2; (e) 1,3,5-Me3C6H3; (f) 1,2,3-Me3C6H3. Treatment of 2 with xylyl isocyanide (XylNC) in the presence of NaPF6 produced the F-coordinated complex [(η6-arene)RuCl]2(μ-dpmf)(PF6)2 3a without containing XylNC. Reactions of 1 with 1,1′-bis(diphenylphosphino)ferrocene (dppf) formed the bridged complexes [(arene)RuCl2]2(μ-dppf)] 4, as well as the dpmf complexes. The similar reactions in the presence of NaPF6 gave the chelated complexes [(η6-arene)RuCl(dppf-P,P′)](PF6) 5. Crystal structures of 2a, 2d·2CH2Cl2, 4a·CH2Cl2 and 5b were confirmed by X-ray analyses and they have three-legged piano-stool structures. Crystal data are as follows: 2a triclinic, space group P 1 , with a=12.802(6), b=19.111(6), c=11.438(4) A, α=98.93(3), β=108.57(3), γ=90.42(3)°, V=2615(1) A3, Z=2 [R=0.051, Rw=0.052 for 4114 independent reflections with I>3.0σ(I)]; 2d·2CH2Cl2 monoclinic, space group C2/c, a=38.379(6), b=9.903(3), c=17.381(4) A, β=113.91(1)°, V=6038 A3 and Z=4 [R=0.057, Rw=0.054 for 1882 independent reflections with I>3.0σ(I)]; 4a·CH2Cl2 triclinic P 1 , with a=15.044(7), b=17.664(3), c=10.586(2) A, α=99.64(2), β=95.85(2), γ=94.74(2)°, V=2744(1) A3, Z=2 [R=0.065, Rw=0.072 for 4301 independent reflections I>3.0σ(I)]; 5b monoclinic, space group P21/n, a=15.036(4), b=17.192(5), c=15.983(3) A, β=92.92(2)°, V=4126(1) A3, Z=4 [R=0.070, Rw=0.079 for 3389 independent reflections I>3σ(I)]. Conformation of the ferrocenyl skeletons were determined by dihedral angles containing two Cp rings. In cyclic voltammertry (CV) of these complexes the Fe(II)/Fe(III) redox couples were quasi-reversible, but the Ru moieties were irreversible.

Studies on interactions of isocyanide with transition metal complexes: XXXVI. Spontaneous successive insertion of isocyanide into palladium-carbon σ-bond

Abstract Reaction of trans -Pd(PPh 3 ) 2 I(CH 3 ) ( 1a ) with 2,6-xylyl isocyanide in a 1:1 molar ratio led to a spontaneous insertion of isocyanides into a Pdue5f8C bond to give the tris-imino insertion product 2a . The structure was determined by an X-ray analysis. The crystals are triclinic with space group P 1 ( a = 14.638(9), b = 15.662(7), c = 7.895(3) A, α = 85.06(6), β = 82.84(4), γ = 102.4(4)°, and Z = 2; R = 0.066 for 2076 independent reflections with F 0 > 5σ( F 0 ). The tris-imino group acts as a bidentate ligand through C- and N-coordinations. The 2-methyl-1-naphthyl complex, trans -Pd(PPh 3 )Br(2-CH 3 C 10 H 9 ) reacted with 2,6-xylyl isocyanide to give a bis-imino complex containing μ 2 -Br bridging ligands. Using p -nitirophenyl isocyanide, the reaction produced a mono-imino compound. Reaction of 2a with CuCl 2 gave a mixed metal complex, in which the copper(II) atom is coordinated to two neighbouring imino-nitrogens.

Reactions of bis[dichloro(η5-pentamethylcyclopentadienyl)iridium(III)] with bulky and highly basic aromatic phosphines containing ortho-methoxy groups

Abstract Reaction of [Cp*IrCl 2 ] 2 1 (Cp*=C 5 Me 5 ) with (2,6-dimethoxyphenyl)diphenylphosphine (MDMPP) at room temperature gave a monohapto-complex [Cp*IrCl 2 (MDMPP- P )] 2a , whereas the reaction with bis(2,6-dimethoxyphenyl)phenylphosphine (BDMPP) led to loss of one molecule of CH 3 Cl to give Cp*IrCl[P(C 6 H 3 -2-O-6-OMe){C 6 H 3 -2,6-(MeO) 2 } Ph] (=Cp*IrCl(BDMPP-κ 2 P , O ) 3b with a chelated P , O coordination, in which the structure was confirmed by an X-ray analysis: a =15.994(3) A, b =10.471(2) A, c =17.727(3) A, β =94.12(1)°, monoclinic, P 2 1 / n , Z =4, R =0.032. Tris(2,6-dimethoxyphenyl)phosphine (TDMPP) reacted with 1 to afford Cp*Ir[P(C 6 H 3 -2-O-6-OMe) 2 {C 6 H 3 -2,6-(MeO) 2 }] (=Cp*IrCl(TDMPP-κ 3 P , O , O ′) 4c . It was confirmed by an X-ray analysis that the molecule has a trihapto coordination ( P , O , O ′) derived from demethylation of two molecules of CH 3 Cl: a =17.55(1) A, b =21.22(3) A, c =15.92(2) A, orthorhombic, Pbcn , Z =8, R =0.044. Complex 1 was treated with MDMPP, BDMPP or TDMPP in acetone in the presence of a PF 6 anion to give salt-like complexes [Cp*IrCl(XDMPP-κ 2 P , O Me)][PF 6 ] 5 (X=M, B, T) with a P,O coordination. The structures of 5b and 5c ·CHCl 3 were confirmed by X-ray analyses: for 5b (X=B), a =11.679(2) A, b =15.389(4) A, c =10.251(3) A, α =103.92(2)°, β =91.76(2)°, γ =105.15(2)°, triclinic, P 1, Z =2, R =0.046; for 5c ·CHCl 3 (X=T), a =14.730(7) A, b =18.55(2) A, c =15.753(9) A, β =91.76(2)°, γ =105.45(5)°, monoclinic, P 2 1 / n , Z =4, R =0.048. In complexes 5a and 5b the exchange between free and coordinated OMe groups was observed, whereas in 5c such exchange was not observed. Complex 2a readily reacted with Lewis bases (L) such as isocyanide and CO in the presence of a PF 6 anion to produce [Cp*IrCl(L)(MDMPP- P )][PF 6 ] 6 .