Synthesis and structure of an air-stable organoantimony complex and its use as a catalyst for direct diastereoselective Mannich reactions in water Jun Xia a , Renhua Qiu a , Shuangfeng Yin a, * , Xiaowen Zhang a , Shenglian Luo a , Chak-Tong Au a,b , Kai Xia a , Wai-Yeung Wong c a College of Chemistry and Chemical Engineering, Hunan University, Changsha 410082, PR China b Department of Chemistry, Hong Kong Baptist University, Kowloon Tong, Hong Kong, PR China c Department of Chemistry, Centre for Advanced Luminescence Materials, Hong Kong Baptist University, Kowloon Tong, Hong Kong, PR China article info Article history: Received 2 February 2010 Received in revised form 2 March 2010 Accepted 2 March 2010 Available online 6 March 2010 Keywords: Organoantimony Lewis acid Direct Mannich reaction Diastereoselectivity Catalyst abstract An air-stable organoantimony complex with a 5,6,7,12-tetrahydrodibenzo[c,f][1,5]azastibocine frame- work was synthesized, characterized, and found to exhibit high catalytic efficiency towards one-pot Man- nich reaction with high diastereoselectivity in water. The catalyst can be recycled 10 times without showing any appreciable loss of efficiency. This catalytic system affords a simple and efficient approach for the synthesis of b-amino ketones. Ó 2010 Elsevier B.V. All rights reserved. 1. Introduction The Mannich reaction is a classical method for the prepara- tion of b-amino carbonyl compounds as well as an important route for the formation of carbon–carbon bonds [1–4]. Nonethe- less, the approach reported in the literature has shortcomings such as harsh conditions, long reaction time, and side reactions (such as aldol reaction) [1]. Hence the development of synthetic routes free of such drawbacks is highly desirable. Recent devel- opment of metal-free organocatalytic Mannich reaction has been reviewed by Ting and Schaus [2]. Impressive accomplishments have been made in diasteroselective synthesis over various Lewis acid catalysts [3]. Shibasaki and co-workers reported for the first time the direct Mannich-type reaction of unmodified ketones catalyzed by lanthanum complex [5]. Kobayashi et al. reported that FeCl 2 together with a (R)-3.3 0 -I 2 BINOL complex is effective for the Mannich reaction of imines with silyl enolates [6]. Simi- lar reactions were performed by using a novel chiral zirconium catalyst for the production of b-amino ester derivatives [7,8]. List and co-workers reported that the proline-catalyzed asymmetric Mannich reactions (with different ketones) displayed high enantioselectivity but accompanied by some aldol products [9,10]. Notz et al. and Ibrahem et al. disclosed that cyclic chiral amines can catalyze the direct Mannich reaction with good enantioselectivity under mild conditions [11,12]. Acidic ionic li- quid as an effective organocatalyst for the one-pot Mannich reaction has also been developed [13]. Due to the use of organic solvents, the reactions have to be conducted at relatively low temperatures and under strictly anhydrous conditions. Recently, we reported a cationic organobismuth perchlorate complex ([S(CH 2 C 6 H 4 ) 2 Bi(OH 2 )] + [ClO 4 ]  ) that is catalytically highly active, giving anti/syn molar ratio 6 95/5 in the direct diastereoselective Mannich reaction [14]. On the other hand, no diastereoselectivity was observed over covalent organobismuth(III) perfluorooctane- sulfonate (C 6 H 11 N(CH 2 C 6 H 4 ) 2 Bi(OSO 2 C 8 F 17 )) although its cata- lytic efficiency towards the Mannich-type reactions was high [15]. Considering that antimony and bismuth are both group-15 ele- ments, we turned our attention to the synthesis and application of new organoantimony compounds. Organoantimony compounds have been synthesized and used in organic reaction as well as in the fields of catalysis, biochemistry and medicine [16–26]. Most of the applications are focused on in vitro antitumour activity and organic reactivity [21–24]. Kakusawa et al. reported that hypervalent organoantimony compounds with a tetra- hydrodibenzo[c,f][1,5]azastibocine framework are agents highly efficient for cross-coupling reactions [27]. Recently, organoantimo- ny oxide was synthesized and found to be recoverable reagent effi- cient for CO 2 chemical fixation [28]. Ionic organoantimony 0022-328X/$ - see front matter Ó 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.jorganchem.2010.03.003 * Corresponding author. Tel./fax: +86 731 88821310. E-mail address: sfyin73@yahoo.com.cn (S. Yin). Journal of Organometallic Chemistry 695 (2010) 1487–1492 Contents lists available at ScienceDirect Journal of Organometallic Chemistry journal homepage: www.elsevier.com/locate/jorganchem