Tishchenko reaction of aldehydes in the presence of an amino alcohol-based Ir bifunctional catalyst was developed. The reaction proceeds with 1 mol% of the catalyst and 20-30 mol% of K 2 CO 3 in acetonitrile at room temperature to give the corresponding dimeric esters in good yield.In 1906, Tischtschenko reported the conversion of aldehydes to dimeric esters in the presence of Al alkoxide and Mg alkoxide catalysts. 1,2 Since then, the Tishchenko reaction has been used as an efficient method for the preparation of dimeric esters in industry. Other catalyst systems have also been developed, including boric acid 3 and transition metal catalysts such as Fe, 4 Ru, 5 Zr, 6 lanthanide, 7 Ir(I), 8 and Os, 9 and more recently, sophisticated Al alkoxide catalysts. 10 Although the catalyst system developed by Shvo has excellent activity, 5b heating is required. Some catalyst systems can be used at room temperature, but the reaction of simple aliphatic aldehydes is suffered from the formation of aldol-related products, 7 and the reactions of aromatic aldehydes proceed in only modest yields. 10 Thus, there is still great room for improvement of the synthetic efficiency. Herein, we wish to report a mild Tishchenko reaction with broad generality using an iridium complex developed by our group. 11,12 Scheme 1When a MeCN suspension of 3-phenylpropanal (1, Scheme 1), K 2 CO 3 , and an Ir catalyst prepared from 3 11a and 2-propanol (1:K 2 CO 3 :Ir = 100:30:1 mol ratio) was allowed to stand at room temperature for 13 hours, 3-phenylpropyl 3-phenylpropanoate (2a) was obtained in 91% yield. The reaction in CH 2 Cl 2 gave a higher yield of 95%. Other solvents such as hexane, toluene, THF, EtOAc, acetone, and butanone are usable, and the reactions in these solvents proceeded in 79-87% yield. However, the reaction in t-BuOH gave 2a in only 40% yield, accompanied with formation of aldol-related products. To obtain the dimeric ester in high yield, the use of K 2 CO 3 is crucial. Without the base, the reaction proceeded in only 6% yield after 10 hours. However, the yield increased to 85% in the presence of just 10 mol% of K 2 CO 3 . 13 Having succeeded in optimizing the reaction conditions, we next investigated Tishchenko reaction of other substrates. As shown in Table 1, both aliphatic and aromatic aldehydes could be converted to the corresponding dimeric esters in high yields. 14 Thus, the reaction of the unsaturated aldehyde 1b gave 2b in 90% yield, albeit with a longer reaction time (entry 2). The product 2b is a precursor of epoxy resin. Various aromatic aldehydes were converted to the corresponding dimeric esters in good yields (entries 3-8). Thus, the reaction of aromatic aldehydes with a substituent such as alkyl, sulfide, halogen, or nitro proceeded without any difficulties. As anticipated from the literature, 10b however, a,b-unsaturated aldehyde such as cinnamaldehyde is a difficult substrate and the reaction of 1i gave 2i in only 34% yield, along with a mixture of partially or fully saturated esters in 19% yield (entry 9).A p...
I r i d i u m -C a t a l y z e d O x i d a t i v e D i m e r i z a t i o n o f P r i m a r y A l c o h o l s t o E s t e r sAbstract: Oxidative dimerization of primary alcohols with 2-butanone in the presence of an amino alcohol-based Ir bifunctional catalyst was accomplished for the first time. The reaction proceeds with 1-2 mol% of the catalyst and 0.3 mol equivalents of K 2 CO 3 in 2-butanone at room temperature to give the corresponding dimeric esters in 30-93% yield.
Carboxylic acid esters Q 0530 Tishchenko Reaction Using an Iridium-Ligand Bifunctional Catalyst. -The title reaction is effective with a wide range of aldehydes and is a simple and economical process. -(SUZUKI*, T.; YAMADA, T.; MATSUO, T.; WATANABE, K.; KATOH, T.; Synlett 2005, 9, 1450-1452; Tohoku Pharm. Univ., Aoba, Sendai 981, Japan; Eng.) -K. Woydowski 41-084
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