Dae-Yon Lee

Chelation-assisted carbon-hydrogen and carbon-carbon bond activation by transition metal catalysts.

Herein we describe the chelation-assisted C-H and C-C bond activation of carbonyl compounds by Rh1 catalysts. Hydroacylation of olefins was accomplished by utilizing 2-amino-3-picoline as a chelation auxiliary. The same strategy was employed for the C-C bond activation of unstrained ketones. Allylamine 24 was devised as a synthon of formaldehyde. Hydroiminoacylation of alkynes with allylamine 24 was applied to the alkyne cleavage by the aid of cyclohexylamine.

HYDROACYLATION OF 1-ALKENE WITH HETEROAROMATIC ALDEHYDE BY RH(I) AND ADDITIVES

Abstract Hydroacylation of 1-alkene with a heteroaromatic aldehyde such as pyridinecarboxaldehyde, thiophenecarboxaldehyde and furfural derivatives under cocatalyst of Wilkinsons complex and 2-amino-3-picoline gave poor yield of hydroacylated product. The addition of a catalytic amount of bis-(cyclopentadienyl)zirconium dichloride or bis(cyclopentadienyl)titanium dichloride as an additive dramatically increased the yield of the hydroacylated ketone product.

Solvent-free chelation-assisted intermolecular hydroacylation: effect of microwave irradiation in the synthesis of ketone from aldehyde and 1-alkene by Rh(I) complex

Abstract As a green alternative to classical homogeneous catalyst in toluene in closed vessels, the intermolecular hydroacylation of 1-alkenes with aldehydes by Rh(I) complex (Wilkinson catalyst) can be realized efficiently under solvent-free conditions. When coupled to microwave activation, it results in a serious improvement when compared to classical conditions.

Chelation-assisted carbon-carbon bond activation by Rh(I) catalysts

Abstract Herein described is the chelation-assisted CC bond activation of unstrained ketones under the co-catalyst system of Rh(PPh 3 ) 3 Cl and 2-amino-3-picoline ( 1 ). This reaction is based on the strategy we recently developed in hydroacylation with aldehydes in which 2-aminopyridine derivatives function as chelation-assistant tools. Unstrained ketones having a β-hydrogen gave rise to alkyl-exchanged ketones via this CC bond activation under an excess of external olefins. In the absence of external olefins, cycloheptanone underwent a ring contraction to generate five- and six-membered cyclic ketones. Instead of unstrained ketones, sec -alcohols were also employed as a substrate for this CC bond activation via hydrogen transfer. The reaction of allylamine derivatives under [Rh(C 8 H 14 ) 2 Cl] 2 and PCy 3 afforded symmetric dialkyl ketones via a series of reaction such as olefin isomerization, CH bond activation, and CC bond activation. The key intermediate, the imine derived from 1 was generated from a primary amine through dehydrogenation followed by transimination. Consequently, the Rh(I)-catalyzed CC bond activation of unstrained ketones and their equivalents was demonstrated by utilizing a chelation-assistance strategy.

Solvent-free chelation-assisted hydroacylation of olefin by rhodium(I) catalyst under microwave irradiation

A solvent-free protocol for the rhodium(I)-catalyzed intermolecular hydroacylation was achieved under microwave irradiation to furnish various ketones in high yields. The reactivity was improved by the addition of aniline as well as 2-amino-3-picoline and benzoic acid to induce a transimination, which facilitates the formation of intermediate aldimine. A comparison of the reactivity between the reaction performed under the conventional heating mode and the microwave irradiation using monomode reactor revealed an important specific microwave effect during the chelation-assisted hydroacylation. It is supposed that the observed specific microwave effect mainly originates from the formation of aldimine by condensation of aldehyde and amine, which leads to a development of charges in the transition state. This result confirms that the rate-determining step of the reaction is the initial condensation step rather than the subsequent hydroiminoacylation step.