Lewis Acid-Promoted [2 + 1] Cycloaddition Reactions of a 1-Seleno-2-silylethene to 2-Phosphonoacrylates: Stereoselective Synthesis of a Novel Functionalized α-Aminocyclopropanephosphonic Acid
Stereoselective SnCl(4)-promoted [2 + 1] cycloaddition reactions of 1-seleno-2-silylethene 1 with 2-phosphonoacrylates 2 lead to highly functionalized cyclopropanephosphonate esters 3 in high yields. The cyclopropane products 3 are potentially versatile starting materials for biologically important compounds. Stereoselectivesynthesis of a novel functionalized alpha-aminophosphonic acid derivative
An all-cis-functionalized cyclopropane template to connect the three peptide chains in a collagen model is designed. Stereoselective synthesis of cyclopropane-assembled collagen-model 2b with the minimum unit of Gly-Pro-Pro is based on a novel 1-seleno-2-silylethene [2 + 1] cycloaddition strategy. Reaction of the 1-seleno-2-silylethene 4 with triester-substituted olefin 5 in the presence of ZnI2 gives [2 + 1] cycloadduct 6 stereoselectively. Cyclopropane 6 is selectively transformed into triol 10 in four steps. The reaction of 10 and three equivalents of N-Boc-Pro-Pro-Gly-OH in the presence of WSC–DMAP and subsequent deprotection with TFA gives 2b.
Highly Efficient [2+1] Cycloaddition Reactions of a 1-Seleno-2-silylethene to 2-Phosphonoacrylates: Synthesis of Novel Functionalized Cyclopropanephosphonic Acid Esters
A novel one-step [2 + 1] cycloaddition synthesis of cyclopropanes has been developed. Reaction of (E)-1-(phenylseleno)-2-silylethenes 1a,b with vinyl ketones 2a-d and acrolein (2e) in the presence of SnCl4 gave cyclopropane products by a formal [2 + 1] cycloaddition accompanied by 1,2-silicon migration rather than by [2 + 2] cycloaddition. This facile 1,2-silicon shift is rationalized by a remarkable selenium effect. A generated beta-silicon-stabilized zwitterion A is transformed by a 1,2-silicon shift to the more stable selenium-bridged intermediate C. Ab initio MO calculations for model compounds clearly demonstrate that the intermediate C is more stable than A. The selenium-bridged geometry of C shows that preference is for formation of a cyclopropane ring instead of a cyclobutane ring.
Chiral Synthesis of Cyclopropanes. Stereoselective [2 + 1] Cycloaddition Reactions of 1-Seleno-2-silylethenes with Di-(−)-menthyl Ethene-1,1-dicarboxylates
作者:Shoko Yamazaki、Hitomi Kataoka、Shinichi Yamabe
DOI:10.1021/jo9820925
日期:1999.4.1
Reaction of 1-seleno-2-silylethenes 1 with the chiral electrophiles 2, 3, and 4 derived from (-)menthol, in the presence of zinc halides gave the cyclopropane products 5, 6, and 7, respectively, with high diastereoselectivity. The absolute configuration of 5a, prepared by the reaction of 1-(phenylseleno)-2-(trimethylsilyl)ethene (la) and di-(-)-menthyl methylenemalonate (2), was determined to be 2S by conversion to the known chiral compound 11. The proposed mechanism, involving fixation of the (-)-menthyl group to the C=C plane by the Lewis acid in the addition step, is consistent with the experimental observations. A selenium-participating secondary orbital interaction in the synclinal addition path was elucidated by ab initio calculations and explained the observed diasteroselectivity.