Metal-free catalytic reduction of aldehydes, ketones,
aldimines, and ketimines
Hiroaki Matsuoka a, Kazuhiro Kondo a,b,
*
a Graduate School of Medical Sciences, Nagoya City University, Nagoya 467-8601, Japan
b Graduate School of Pharmaceutical Sciences, Nagoya City University, Nagoya 467-8603, Japan
Received 18 March 2010
Abstract
The metal-free combination of catalytic amounts of PPh3, B(C6F5)3, and PhSiH3 can efficiently hydrosilylate aldehydes,
ketones, aldimines and ketimines to afford the corresponding reduction products in good yields.
# 2010 Kazuhiro Kondo. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved.
Keywords: Metal-free hydrosilylation; Reduction; Ketone; Ketimine
Reduction of C O and C N bonds to alcohols and amines, respectively, is an important reaction in organic
synthesis [1]. Among the available reduction methods, hydrosilylation is very useful because of its less excessive
reaction, as compared with other reduction methods such as the one that uses LiAlH4. Thus far, considerable research
has focused on the development of hydrosilylation using metals [1]. Herein, we report the metal-free catalytic
reduction (hydrosilylation) [2–4] of aldehydes, ketones, aldimines and ketimines.
1. Results and discussion
We investigated the combinations of non-metal Lewis acids and bases in the activation of a substrate and a silane,
respectively [5]. After intensive screening, the combination of B(C6F5)3 as a Lewis acid, PPh3 as a Lewis base [6],
PhSiH3 as a hydride source and toluene as a solvent was found to afford the best yield: the reaction conversion within
2 mol equiv of PhSiH3 was low. Representative screening results are shown in entries 1–8 of Table 1. Absence of PPh3
or B(C6F5)3 resulted in no reaction (entries 7 and 8). Although bis-phosphines were also found to be effective as shown
in entries 9 and 10, PPh3 was chosen from the cost perspective.
As shown in Table 2, the reaction under the optimized conditions proved to be general and may be applied to a broad
range of ketones, aldehydes, aldimines and ketimines. Specifically, the reaction proceeds smoothly under mild
conditions with a synthetically acceptable catalyst loading (5 mol.%). Various acetophenone derivatives 1b–1e,
aliphatic acyclic and cyclic ketones 1f–1 h, aromatic aldehydes, aliphatic and a,b-unsaturated aldehydes 1i–1o,
* Corresponding author.
1001-8417/$ – see front matter # 2010 Kazuhiro Kondo. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved.