Selectivity in the electrochemical deprotection of cinnamyl groups from oxygen and nitrogen functionalities: carbonates versus carbamates Petr Cankar ˇ, a Diane Dubas, b Scott C. Banfield, b MÕhamed Chahma b and Tomas Hudlicky b, * a Department of Chemistry, Palacky University, Olomouc, Czech Republic b Department of Chemistry, Brock University, St. Catharines, Ont., Canada L2S 3A1 Received 6 July 2005; revised 29 July 2005; accepted 2 August 2005 Available online 19 August 2005 Abstract—Several cinnamyloxy carbamates and carbonates were subjected to electrochemical reduction, and the reductive fate of the cinnamyl group was investigated. Complete selectivity was observed in the removal of the cinnamyl group from oxygen versus nitrogen. Ó 2005 Elsevier Ltd. All rights reserved. 1. Introduction The cinnamyl group has been shown to be easily and selectively removed by electrochemical reduction from oxygen and nitrogen atoms in preference to all other allylic systems. 1 We have shown that such reductions are also selective toward removal of cinnamyl groups in which the double bond is not further substituted or contained within a ring. Such selectivity is unusual com- pared to other methods of reduction (dissolved metal, and palladium- 2–5 or ruthenium- 6 mediated processes). Further study led to investigations of selectivity in elec- trochemical reductions of cinnamyl groups from ethers versus esters, ethers versus amines, cinnamyl ethers ver- sus benzyl ethers, and cinnamyl versus allyl carba- mates. 7 We have shown that reduction of cinnamyl groups from oxygen occurs in preference to their removal from nitrogen and that the cinnamyloxycar- bonyl (COC) is reduced with complete selectivity in preference to allyloxycarbonyl (Alloc), which is usu- ally removed via palladium catalysis, as shown in Figure 1. In this letter, we report the outcome of electrochemical reductions of cinnamyl carbamates and cinnamyl car- bonates and note the difference in the mechanism of reduction of the cinnamyl groups from these two func- tionalities, as opposed to the fate of their removal from esters and ethers. 2. Results and discussion In an earlier letter, 7 we reported the electrochemical behavior of 3, the linear sweep voltammogram (LSV) of which exhibited three waves (À2.30, À2.73, and À2.93 V vs AgCl/Ag). Reduction at À2.30 V furnished aminoalcohol 4 with apparent lack of selectivity, as shown in Figure 2. Reinvestigation of these results un- der slightly different conditions (absence of phenol as proton source) revealed three waves at À2.68, À2.79, 0040-4039/$ - see front matter Ó 2005 Elsevier Ltd. All rights reserved. doi:10.1016/j.tetlet.2005.08.020 Keywords: Electrochemical reduction; Cinnamyloxy carbonate reduc- tive deprotection; Cinnamyloxy carbamate reductive deprotection. * Corresponding author. Tel.: +1 905 688 5550x4956; fax: +1 905 984 4841; e-mail addresses: banfield_scott@yahoo.ca; thudlicky@ brocku.ca N N O O O O Ph 1 N N O O H 2 -2.45 V, Hg CH 3 CN 79 % Figure 1. Electrochemical reduction of cinnamyl versus allyl carbamates. Tetrahedron Letters 46 (2005) 6851–6854 Tetrahedron Letters