%0 Journal Article
%T Regioselective and Chemoselective Reduction of , -Unsaturated Carbonyl Compounds by /Ba as a Reducing System
%A Mina Mohamadi
%A Davood Setamdideh
%A Behrooz Khezri
%J Organic Chemistry International
%D 2013
%I Hindawi Publishing Corporation
%R 10.1155/2013/127585
%X , -unsaturated aldehydes and ketones are regioselectively reduced to the corresponding allylic alcohols with /Ba system in CH3CN. This system is also efficient for the chemoselective reduction of enals in the presence of enones at room temperature. 1. Introduction Reduction of , -unsaturated carbonyl compounds widely has been carried out by different reducing agents. This reaction is highly solvent dependent and generally does not result in a useful regioselectivity [1¨C3]. It can follow two pathways: addition to carbonyl group (1,2-reduction) to give allylic alcohols or addition to the conjugated double bond (1,4-addition) to give saturated carbonyl compounds. To control the reducing potential and selectivity of metal hydrides specially NaBH4 (common reducing agent) for the 1,2-reduction of conjugated carbonyl compounds, numerous hydroborate agents have been developed in the following ways: (a) by the replacement of hydride(s) with bulky substituents or electron-withdrawing/releasing groups in order to discriminate between the structural and electronic environments of carbonyl groups [4¨C7]; (b) combination with Lewis acids [8¨C10] such as Luche reduction [11, 12] and mixed solvent systems [1, 2]; (c) use of transition metal hydroborates and their new modifications [13], (d) use of phosphonium tetrahydroborates [14, 15], and finally (e) immobilization on an anion exchange resin [16]. In this context and continuation of our studies for the reduction of functional groups in organic synthesis [17¨C20], we decided to apply NaBH4/Ba(OAc)2 as new a reducing system for reduction of ¦Á,¦Â-unsaturated carbonyl compounds. Now we wish to report an efficient method for the regioselective reduction of ¦Á,¦Â-unsaturated aldehydes and ketones by NaBH4/Ba(OAc)2 as a new reducing system. 2. Experimental 2.1. General All substrates and reagents were purchased from commercial sources with the best quality and used without further purification. IR and 1H£¿NMR spectra were recorded on PerkinElmer FT-IR RXI and 300£¿MHz Bruker spectrometers, respectively. The products were characterized by their 1H£¿NMR or IR spectra and comparison with authentic samples (melting or boiling points). Organic layers were dried over anhydrous sodium sulfate. All yields referred to isolated pure products. TLC was applied for the purity determination of substrates, products, and reaction monitoring over silica gel 60 aluminum sheet. 2.2. A Typical Procedure for Regioselective 1,2-Reduction of Conjugated Carbonyl Compounds with NaBH4/Ba(OAc)2 as a New Reducing System In a round-bottomed flask (10£¿mL)
%U http://www.hindawi.com/journals/oci/2013/127585/