Facile Bifunctional Addition of Lactones and Esters at Low Temperatures. The First Intermediates in Lactone/Ester Hydrogenations

Abstract

The bifunctional addition of lactones/esters is unexpectedly facile at low temperatures. Catalytic hydrogenations of esters can be carried out under mild conditions, e.g. -20 °C under 4 atm of H 2 , but product inhibition slows these reactions oVer time.

A Highly Active Catalyst for the Hydrogenation of Amides to Alcohols and Amines

“…The complex 1 also catalyzes the hydrogenation of ethyl hexanoate under 4 atm H 2 below a temperature of 0 8C, [13] and the monohydrogenation of meso-cyclic imides at 0 8C. [10] We report herein the results of our study of 1 and related compounds as catalysts for the hydrogenation of amides.…”

“…Compound 2 a was hydrogenated with a turnover number (TON) of approximately 27 to give the ring-opened N-methanesulfonyl amino alcohol product when using 2 mol % These results are in contrast to the high activity of 1 towards the reduction of ketones, esters, and imides in THF. [10,12,13] We reasoned that catalysts such as 1 are intrinsically active towards amide hydrogenation, but they decompose [12] at the higher temperaturerequired for this transformation. We hypothesized that tethering the amine and phosphine groups would maintain activity, and prevent dissociative loss of the diamine at high temperatures.…”

“…On the basis of prior studies with ketone and ester substrates and 1, [12,13] we propose the following mechanism for the hydrogenation of amides with 9 (Scheme 1). The first step is a bifunctional-type addition of the amide to 9, thus forming the ruthenium hemiaminaloxide 12 as the net product.…”

Bifunctional Transition Metal-Based Molecular Catalysts for Asymmetric Syntheses

“…15) [61]. Since then, a few groups reported that some combined bifunctional catalysts based on the metal-NH cooperating effect, RuCl 2 (P-N) 2 , PNNP-tetradentate Ru catalyst with a base [62], and RuH 2 (diphosphine)(diamine) [63] promoted efficiently hydrogenation of esters in reasonably good reactivity. We have also found that our bifunctional catalyst Cp*Ru(P-N) and a large amount of base promote the hydrogenation of esters under more forcing conditions [22,56].…”

Reduction of Aromatic and Aliphatic Esters Using the Reducing Systems MoO2(acac)2 or V(O)(OiPr)3 in Combination with 1,1,3,3‐Tetramethyldisiloxane

“…Homogeneous systems with ruthenium complexes have also been employed for this transformation. [12][13][14][15] Silicon chemistry combined with the use of organometallic complexes appears to be a good alternative. [16] Silanes and siloxanes have been employed with different metal sources such as Sb, [17] Rh, [18] Ru, [19] Mn, [20] Ti, [21,22] In, [23] Mo, [24] and Zn [25] to afford alcohols, ethers, or aldehydes.…”