Harada Toshiro, Muramatsu Keiko, Mizunashi Kenta, Kitano Chie, Imaoka Daisuke, Fujiwara Takayuki, Kataoka Hiroshi
Department of Chemistry and Materials Technology, Kyoto Institute of Technology, Matsugasaki, Sakyo-ku, Kyoto 606-8585, Japan.
J Org Chem. 2008 Jan 4;73(1):249-58. doi: 10.1021/jo7021179. Epub 2007 Dec 4.
Atom-economical carbocyclization reactions of omega-iodo-1-alkynes and 1,omega-diiodo-1-alkynes to give products with incorporation of iodine atoms is described. Cycloisomerization of 2-(2-propynyloxy)ethyl iodides is initiated by a catalytic amount of LDA to give 3-(iodomethylene)tetrahydrofurans in high yields. Upon treatment of with a catalytic amount of 1-hexynyllithium, 1,omega-diiodo-1-alkynes efficiently undergo cycloisomerization to give (diiodomethylene)cycloalkanes. The diiodomethylene products are also obtained by iodine atom-transfer-type cyclization of omega-iodo-1-alkynes, using 1-iodo-1-hexyne as an external iodine atom source. Bromine atom-transfer and proton-transfer cyclization proceed as well by employing 1-bromo-1-octyne and 1-octyne, respectively. These reactions are proposed to proceed through a carbenoid-chain process involving exo-cyclization of the lithium acetylide intermediates to give Li,I-alkylidene carbenoids. It is shown that the exo-cyclization proceeded stereospecifically through inversion of the stereochemistry at the electrophilic carbon.
描述了ω-碘代-1-炔烃和1,ω-二碘代-1-炔烃的原子经济性碳环化反应，以得到含有碘原子的产物。2-(2-丙炔氧基)乙基碘的环异构化由催化量的LDA引发，以高产率得到3-(碘亚甲基)四氢呋喃。在用催化量的1-己炔基锂处理时，1,ω-二碘代-1-炔烃有效地进行环异构化，得到(二碘亚甲基)环烷烃。二碘亚甲基产物也可通过ω-碘代-1-炔烃的碘原子转移型环化反应得到，使用1-碘-1-己炔作为外部碘原子源。分别使用1-溴-1-辛炔和1-辛炔也可进行溴原子转移和质子转移环化反应。这些反应被认为是通过一个类卡宾链过程进行的，该过程涉及乙炔锂中间体的外环化，生成Li,I-亚烷基类卡宾。结果表明，外环化反应通过亲电碳上立体化学的反转而立体专一性地进行。
