Tomonori Misaki

Diphenylammonium triflate (DPAT): efficient catalyst for esterification of carboxylic acids and for transesterification of carboxylic esters with nearly equimolar amounts of alcohols

Abstract Diphenylammonium triflate (DPAT) efficiently catalyzed esterification between equimolar amounts of carboxylic acids and alcohols in good to excellent yields under mild reaction conditions. Transesterification of carboxylic esters with a slight excess of alcohols also proceeded using DPAT as catalyst with TMSCl as a co-catalyst.

Direct Asymmetric Aldol Reaction of 5H-Oxazol-4-ones with Aldehydes Catalyzed by Chiral Guanidines

A new chiral bicyclic guanidine-catalyzed direct catalytic aldol reaction of 5H-oxazol-4-ones with aldehydes has been developed. The present aldol reaction proceeds smoothly with high enantioselectivity using bicyclic guanidines bearing a hydroxy group at the appropriate position, and various combinations of 5H-oxazol-4-ones and aldehydes are applicable. The method provides synthetically useful alpha,beta-dihydroxycarboxylates bearing a chiral quaternary stereogenic center at the alpha-carbon atom.

Highly Z-Selective Asymmetric 1,4-Addition Reaction of 5H-Oxazol-4-ones with Alkynyl Carbonyl Compounds Catalyzed by Chiral Guanidines

An asymmetric 1,4-addition reaction of 5H-oxazol-4-ones with alkynyl carbonyl compounds was developed, and, for the first time, high enantiomeric and geometric control was achieved to afford the thermodynamically unstable Z-isomer predominantly using chiral guanidine catalysts bearing a hydroxy group at the appropriate position. The method provides synthetically useful γ-butenolide ester bearing a chiral quaternary stereogenic center.

Pentafluorophenylammonium triflate (PFPAT): an efficient, practical, and cost-effective catalyst for esterification, thioesterification, transesterification, and macrolactone formation

A pentafluorophenylammonium triflate (PFPAT) catalyst (1–10 mol%) efficiently promoted esterification and thioesterification between a 1 : 1 mixture of carboxylic acids and alcohols or thiols in good to excellent yield under mild reaction conditions. Transesterification of carboxylic esters with a slight excess of alcohols (1.5 equiv.) also proceeded using the PFPAT catalyst. The PFPAT-catalyzed 13 to 17 membered macrolactone formation of ω-hydroxycarboxylic acids was successfully performed using 10 mol% of the catalyst (total 44 examples). These catalytic condensations have advantages from the viewpoint of green chemistry. PFPAT organocatalyst is air-stable, cost-effective, easy to handle, and easily removed from the reaction mixtures. The operation is quite simple, because a dehydrating system such as the Dean–Stark apparatus is not necessary.

Direct, practical, and powerful crossed aldol additions between ketones and ketones or aldehydes utilizing environmentally benign TiCl4–Bu3N reagent

Abstract An efficient TiCl4–Bu3N—(cat. TMSCl)-promoted aldol addition between ketones and ketones or aldehydes was performed. This environmentally benign method is advantageous from a green chemical viewpoint with regard to yield, substrates variation, reagent availability, and simple procedures. This method was applied to a short step formal synthesis of (R)-muscone, a natural macrocyclic musk.

General, Robust, and Stereocomplementary Preparation of β-Ketoester Enol Tosylates as Cross-Coupling Partners Utilizing TsCl−N-Methylimidazole Agents

We have developed a general, robust, and cost-effective method for the (E)- or (Z)-stereocomplementary enol tosylation of beta-ketoesters using TsCl- N-methylimidazole (NMI)-Et3N or LiOH. TsCl coupled with NMI formed a highly reactive N-sulfonylammonium intermediate. Stereocongested secondary alcohols were smoothly sulfonylated using Ts(Ms)Cl-NMI-Et3N. beta-Ketoesters underwent (E)-selective tosylation using TsCl-NMI-Et3N and (Z)-selective tosylation using TsCl-NMI-LiOH (total of 23 examples; 60%-99% yield). Stereoretentive Negishi and Sonogashira couplings using enol tosylates proceeded successfully to give trisubstituted alpha,beta-unsaturated esters.

Water-solvent method for tosylation and mesylation of primary alcohols promoted by KOH and catalytic amines

We have developed an efficient water-solvent method for p-toluenesulfonylation (tosylation) and methanesulfonylation (mesylation) of primary alcohols using p-toluenesulfonyl chloride and methanesulfonyl chloride, respectively, promoted by KOH and catalytic amines. The reaction was performed by maintaining the pH at around 10 using a pH controller to prevent the undesirable decomposition of sulfonyl chlorides. Several primary alcohols were smoothly sulfonylated in excellent yield. The choice of the amine catalyst (0.1 equiv.) was important: N,N-dimethylbenzylamine, a sterically unhindered and lipophilic tertiary amine, was effective for the tosylation, whereas N,N-dimethylbutylamine and triethylamine were effective for the mesylation. The present Schotten–Baumann-type method is the first example of catalytic sulfonylation using sulfonyl chlorides, and is a green chemical process due to the use of water as the solvent.

A Highly Efficient Synthesis of Civetone

Abstract A highly efficient synthesis of civetone has been performed by joining two crucial reactions; (a) Ti-Claisen condensation and (b) intramolecular olefin metathesis using Grubbs’ reagent. This synthesis includes not only a stepwise method (A) but also a one-pot method (B).

Ti-direct, powerful, stereoselective aldol-type additions of esters and thioesters to carbonyl compounds: application to the synthesis and evaluation of lactone analogs of jasmone perfumes

An efficient TiCl(4)-Et(3)N or Bu(3)N-promoted aldol-type addition of phenyl and thiophenyl esters or thioaryl esters with aldehydes and ketones was performed (total 46 examples). The present method is advantageous from atom-economical and cost-effective viewpoints; good to excellent yields, moderate to good syn-selectivity, substrate variations, reagent availability, and simple procedures. Utilizing the present reaction as the key step, an efficient short synthesis of three lactone [2(5H)-furanone] analogs of jasmine perfumes was performed. Among them, the lactone analog of cis-jasmone had a unique perfume property (tabac).

Efficient one-step synthesis of trialkylsubstituted 2(5H)-furanones utilizing direct Ti-crossed aldol condensation and its application to the straightforward synthesis of (R)-mintlactone and (R)-menthofuranElectronic supplementary information (ESI) available: calculated structures of 7 and 8. See http://www.rsc.org/suppdata/cc/b2/b208077j/

TiCl4–Bu3N-mediated condensation of ketones with α,α-dimethoxyketones afforded trialkylsubstituted 2(5H)-furanones in a one-pot manner, wherein aldol addition and furanone formation occurred sequentially; its application to straightforward synthesis of (R)-mintlactone and (R)-menthofuran, two representative natural mint perfumes, is demonstrated.