The Study of Intramolecular Free Radical Cyclizations of a-Stannanyl Radicals to Carbonyl and Imine System

• Main Authors: Shau-Hua Ueng, 翁紹華
• Other Authors: Yeun-Min Tsai
• Format: Others
• Language: zh-TW
• Published: 2004
• Online Access: http://ndltd.ncl.edu.tw/handle/93088264933417465808

博士 === 國立臺灣大學 === 化學研究所 === 92 === The mechanism of intramolecular free radical cyclizations of a-stannyl radicals to carbonyl involves an interesting 1,3-stannyl shift. According to our mechanistic study, 1,3-stannyl shift is an irreversible reaction. Competitive cyclization of a,a-dimethylaldehyde system undergoes ring opening rearrangement to give cyclohexylaldehyde 115 and related derivatives 120 、 121. After addition of Lewis acids in the reaction system, the efficiency of competitive cyclization of a-stannyl radical to carbonyl was improved. The ratio of a-stannyl radical addition to carbonyl and carbon-carbon double bond increased from 0.70 to 1.22. In the reaction of a-stannyl radical addition to carbonyl to form six-membered ring, we constructed a sulfonyl group at the a position of the formyl group to inhibit 1,5-H shift in order to increase the cyclization product yield. We obtained 41 % yield of the cyclization product in this system. According to the deuterium experiment, half of the straight reduction product of the a-sulfonylaldehyde was derived from a 1,5-H shift followed by hydrogen abstraction. In contrast, in the w-bromostannylhexanal system all the reduction product was obtained through a 1,5-H shift first. In the case of a-stannyl radical addition to imine system, the reaction of a-stannyl radical addition to hydrazone and oxime ether gave excellent cyclization yield. However, the phenomenon of 1,3-stannyl shift was not observed. There were difficulties in the synthesis and purification of imines 190 、 191, and we obtained massy products in the radical cyclization reactions. a-Stannylxanthate and a-stannylbromide functionalities were unstable under the reaction condition used for the synthesis of phenylimine.