Tatsuo Saito

Organoaluminum‐Mediated Direct Cross‐Coupling Reactions

We present a direct cross-coupling reaction between arylaluminum compounds (ArAlMe2 ⋅LiCl) and organic halides RX (R=aryl, alkenyl, alkynyl; X=I, Br, and Cl) without any external catalyst. The reaction takes place smoothly, simply upon heating, thereby enabling the efficient and chemo-/stereoselective formation of biaryl, alkene, and alkyne coupling products with broad functional group compatibility.

Stereoselective synthesis of trans-fused 7,6,6,7-membered tetracyclic ether, corresponding to the EFGH-ring of gambierol and the BCDE-ring of gambieric acids.

Stereoselective synthesis of a trans-fused 7,6,6,7-membered tetracyclic ether, corresponding to the EFGH-ring of gambierol and the BCDE-ring of gambieric acids, was efficiently accomplished via a two-directional approach. The key reactions were SmI(2)-induced double cyclization for construction of the F- and H-rings and SmI(2)-induced cyclization followed by ring expansion for construction of the E-ring.

Direct Hydroxylation and Amination of Arenes via Deprotonative Cupration

Deprotonative directed ortho cupration of aromatic/heteroaromatic C-H bond and subsequent oxidation with t-BuOOH furnished functionalized phenols in high yields with high regio- and chemoselectivity. DFT calculations revealed that this hydroxylation reaction proceeds via a copper (I → III → I) redox mechanism. Application of this reaction to aromatic C-H amination using BnONH2 efficiently afforded the corresponding primary anilines. These reactions show broad scope and good functional group compatibility. Catalytic versions of these transformations are also demonstrated.

Direct construction of fused indoles by gold-catalyzed cascade cyclization of conjugated diynes.

A gold-catalyzed cascade cyclization of aniline derivatives bearing a conjugated diyne moiety was developed. Following the 5-endo-dig indole formation, subsequent 7-endo-dig cyclization predominated over 6-exo-dig cyclization to give the indole fused with a seven-membered ring in good yields.

Cross-Coupling of Organolithium with Ethers or Aryl Ammonium Salts by C−O or C−N Bond Cleavage

Various aryl-, alkenyl-, and/or alkyllithium species reacted smoothly with aryl and/or benzyl ethers with cleavage of the inert C-O bond to afford cross-coupled products, catalyzed by commercially available [Ni(cod)2 ] (cod=1,5-cyclooctadiene) catalysts with N-heterocyclic carbene (NHC) ligands. Furthermore, the coupling reaction between the aryllithium compounds and aryl ammonium salts proceeded under mild conditions with C-N bond cleavage in the presence of a [Pd(PPh3 )2 Cl2 ] catalyst. These methods enable selective sequential functionalizations of arenes having both C-N and C-O bonds in one pot.

Photodimerization of halogenated anthrone derivatives

Abstract The photochemistry of 10-bromoanthrone (IV), 10,10-dibromoanthrone (III) and 10,10-dichloroanthrone (IX) in dioxane has been investigated. Short time irradiation in the absence of oxygen at wavelengths above 3900 A or 4200 A led to 10,10′-bianthrone (VII), 10,10′-dibromobianthronyl (VI), and 10,10′-dichlorobianthronyl (X), respectively. Further irradiation of 10-bromoanthrone (IV) and 10,10-dibromoanthrone (III) gives quantitatively mesonaphthobianthrone (V). Fluorescence emission spectra indicate that bianthrone (VIII) is the second intermediate in the conversion of 10-bromoanthrone (IV) and 10,10-dibromoanthrone (III) to mesonaphthobianthrone (V). The mechanism of the first step is discussed in detail. Evidence was found that formation of VI and VII proceeds by a mechanism involving the 9-anthryloxy (XIa) and 9-bromo-10-anthryloxy (XIb) radicals from the respective 3 (n,π*). By analogy, a similar mechanism is proposed for the conversion of VI to VIII.

Allylic borylation of tertiary allylic alcohols: a divergent and straightforward access to allylic boronates

A facile and divergent synthetic process for converting tertiary allylic alcohols to multiply substituted allylic boronates is reported. This methodology is especially effective for tertiary alcohol substrates, providing the corresponding allylic boronates in moderate to good yields.

Transition Metal-Free trans-Selective Alkynylboration of Alkynes

We report the first transition metal-free and trans-selective alkynylboration reaction of alkynes. This unprecedented carboboration reaction is enabled by pseudo-intramolecular activation of alkynylboronates using propargylic alcohols. The carboboration affords 4-alkynyl-1,2-oxaborol-2(5H)-ols, which are not only versatile building blocks but also exhibit strong violet-blue fluorescence emission.

Gold-Catalyzed Cyclization of Alkyne Alcohols: Regioselective Construction of Functionalized 6,6- and 6,7-Bicyclic Ethers

We describe an efficient regioselective formation of six-/seven-membered cyclic ethers based on gold-catalyzed intramolecular hydroalkoxylation. Sequential gold-catalyzed cyclization and palladium-catalyzed cross-coupling reactions afforded 6,6-bicyclic ethers, while reversing the reaction sequence (cross-coupling then cyclization) afforded 6,7-bicyclic ethers. This methodology should provide access to a range of functional polycyclic ethers.

Mechanistic Study on Aryl-Exchange Reaction of Diaryl-λ3-iodane with Aryl Iodide

Because of its hyper-leaving ability, as well as its strong oxidizing ability, diaryl(triflato)-λ3-iodane transfers one of the aryl groups to iodoarenes simply upon gentle heating (>85 °C) in nonpolar solvents. We have performed an in-depth mechanistic study of this unusual aryl transfer reaction. A combination of experimental (product analysis, kinetic study, and substituent effects) and density functional theoretical approaches revealed that the reaction proceeds through a concerted bimolecular transition state, in which ipso-carbon binds loosely to both iodine centers. We also evaluated electronic effects on the thermodynamic stability of diaryl-λ3-iodanes.