Yoshinori Yamamoto

SYNTHESIS OF INDENOLS AND INDANONES VIA CATALYTIC CYCLIC VINYLPALLADATION OF AROMATIC ALDEHYDES

o-Bromobenzaldehyde 1, in the presence of a palladium catalyst, smoothly underwent consecutive intermolecular carbopalladation with internal alkynes 2 and then intramolecular nucleophilic vinylpalladation of the aldehyde function to produce the indenol derivatives 4 in high yields. Further heating of 4 under more elevated temperature caused complete isomerization to the corresponding indanones 8. A mechanism for this nucleophilic vinylpalladation of aromatic aldehydes is proposed.

PALLADIUM-CATALYZED ENYNE-YNE 4+2 BENZANNULATION AS A NEW AND GENERAL APPROACH TO POLYSUBSTITUTED BENZENES

Abstract Monosubstituted conjugated enynes smoothly underwent [4+2] homodimerization in the presence of palladium catalyst to give 4, α- and 2,6-disubstituted styrenes. Analogous cross-cycloaddition of conjugated enynes and diynes afforded a variety of polysubstituted benzenes, including phenol and aniline derivatives. Alkynes and diynes in the presence of a palladium catalyst underwent novel formal [2+2+2] sequential cyclotrimerization to afford multifunctional benzenes in one step with high degrees of regio- and chemoselectivities. Mechanisms of these novel transformations are discussed.

Palladium-Catalyzed Hydroalkoxylation of Methylenecyclopropanes.

Hydroalkoxylations proceed by a different path than transition metal catalyzed hydrostannations and hydrosilylations. In the reaction of methylenecyclopropanes 1 with alcohols 2 in the presence of Pd(0), the distal bond in the cyclopropane ring is cleaved, and allyl ether 3 is formed selectively. R(1)=n-C(7)H(15), PhCH(2)CH(2); R(2)=H, PhCH(2)CH(2); R(3)=PhCH(2), CF(3)CH(2), Et(3)Si, n-C(4)H(9), etc.

Unprecedented rearrangement reaction of 2-aziridinemethanols with lower order lithium methylcyanocuprate

Abstract Complementary selectivity can be achieved in ring opening reactions of 2-aziridinemethanols by using either the Gilman reagent or lower order cyanocuprate. In the former case, the usual attack of the Gilman reagent to the substrates 1 and 2 results in the formation of the expected ring opening products ( 3 and 4 ) and ( 7 and 8 ), respectively. In contrast, exposure of both 1 and 2 to the lower order cyanocuprate proceeds in an unprecedented fashion, presumably via epoxides D and G , to yield unexpected secondary alcohols ( 11 and 12 ) as the major products.

Synthesis of cyclic ethers via the palladium catalyzed intramolecular hydrocarbonation of alkoxyallenes

Abstract The intramolecular hydrocarbonation of certain alkoxyallenes (1, 3 and 5), bearing active methine groups at the terminus of the carbon chain, proceeded smoothly in the presence of catalytic amounts of a palladium complex [Pd(OAc)2-dppb] to give 5- to 7-membered cyclic ethers (2, 4 and 6, respectively) in good to high yields.

SN2′ selective alkylation of allylic chlorides and mesylates with RZnX reagents generated from Grignard reagents, zinc chloride, lithium chloride, and Cu(II)-salts

Abstract Treatment of RMgX (1 equiv. R = alkyl; X = Cl, Br) with ZnCl 2 (1 equiv.) in a mixed solvent of THF and Et 2 O leads to a highly turbid white suspension. Addition of LiCl (1∼2 equiv.) solubilizes the insoluble species to yield a colorless clear solution. Addition of a catalytic amount of a Cu(II)-salt followed by allylic halides or mesylates at 0 °C ∼ room temperature yielded S N 2′products in high yields. Application for the synthesis of ( E )-alkene dipeptide isosteres is also reported.

“Higher order” zinc cuprates involving lithium chloride: Synthesis of (E)-alkene dipeptide isosteres free from reductive elimination products

Abstract The “higher order” organozinc cuprates, R 2 Cu(CN)(ZnCl) 2 ·2Mg(X)Cl·nLiCl, derived from admixture of LiCl (1∼2 equiv.), ZnCl 2 (1 equiv.), RMgX (1 equiv.), and CuCN (0.5 equiv.) in a mixed solvent of THF and Et 2 O exhibit high diastereoselection of up to > 99: 1 in the synthesis of (E)-alkene dipeptide isosteres from γ-mesyloxy-α,β-unsaturated esters. Addition of lithium chloride is essential for the preparation of clear solutions of reagents.

PALLADIUM-CATALYZED BENZANNULATION OF CONJUGATED ENYNES. ENHANCED REACTIVITY OF ALKOXYCARBONYL- AND CYANOENYNES

Abstract We report the high reactivity of alkoxycarbonyl- and cyanoenynes in the homo-benzannulation of conjugated enynes. The introduction of these electron-withdrawing groups enabled us to carry out the benzannulation of 1-substituted enynes as well as 1,2- and 2,4-disubstituted enynes, which have much lower reactivity compared to 2- or 4-monosubstituted enynes. Polysubstituted benzenes were prepared in a highly regioselective manner in good to excellent yields.

INTER- AND INTRAMOLECULAR PALLADIUM-CATALYZED HYDROCARBONATION OF METHYLENECYCLOPROPANES WITH CARBON PRONUCLEOPHILES

Abstract The inter- and intramolecular additions of pronucleophiles to methylenecyclopropanes proceeded smoothly in the presence of catalytic amounts of Pd(PPh3)4, affording hydrocarbonation products in good to high yields. The ring opening of methylenecyclopropanes mainly occurred at the distal position to the exomethylene. In some cases, proximal bond cleavage also took place. The mode of ring opening depended upon both the structure of the pronucleophile and the substituent at the exomethylene carbon.

A chemical scale for electron-transfer ability of methylcopper reagents

The ratio of methyl transfer (2) and reduction (3) products in the reaction of trimethoxycarbonylethylene 1 with methylcopper reagents MeCuLn varies with the copper species, and decreased in the following order: MeCu(CN)Li > MeCu > Me2Cu(CN)Li2≫ Me2CuLi > Me3CuLi2.