a-錫基自由基加成到羰基與亞胺系統的分子內自由基環化反應研究
The Study of Intramolecular Free Radical Cyclizations of a-Stannanyl Radicals to Carbonyl and Imine System
Date Issued
2004
Date
2004
Author(s)
Ueng, Shau-Hua
DOI
zh-TW
Abstract
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.
Subjects
a-錫基自由基
羰基
亞胺
環化反應
Carbonyl
a-Stannanyl Radicals
Imine
Cyclizations
Type
thesis