Stereoselective synthesis of tetralins using cationic cyclisations
摘要:
Tetralins, including the terpene calamenene, were prepared by 6-endo cationic cyclisations, effected by addition of an l(l) reagent to alkenylarenes, followed by reductive deiodination. An activating group on the arene was required for efficient cationic cyclisation. Good diastereoselectivity, relative to a chiral centre in the chain linking the alkene to the arene, was observed, with Z-alkenes giving predominantly 1,4-cis disubstituted tetralins, and E-alkenes giving predominantly 1,4-trans derivatives. Analogous 6-exo cationic cyclisations proved very limited in scope. (C) 2003 Elsevier Ltd. All rights reserved.
Aryl- and alkenyl substituted oxiranes, when submitted to treatment with superbasic reagents, undergo a highly regio- and stereoselective rearrangement leading to cyclopropylmethanol derivatives. The process can also be applied to mono- and dihydroxy substituted substrates thus leading to polyhydroxylated cyclopropanes.
Mild and simple catalytic systems consisting of molybdenum(VI) dichloride dioxide [MoO2Cl2] as a catalyst and a phosphine as reductant have been developed for the stereospecificdeoxygenation of epoxides to alkenes. The reactions using 1,2‐bis(diphenylphosphino)ethane (dppe) and triphenylphosphine (PPh3) proceed with retention and inversion of stereochemistry, respectively. The mild reaction tolerates
Stereospecific Deoxygenation of Aliphatic Epoxides to Alkenes under Rhenium Catalysis
作者:Takuya Nakagiri、Masahito Murai、Kazuhiko Takai
DOI:10.1021/acs.orglett.5b01583
日期:2015.7.2
is effective for the deoxygenation of unactivated aliphatic epoxides to alkenes. The reaction proceeds stereospecifically with variously substituted epoxides under neutral conditions and is compatible with various functional groups. Protection and deprotection of a double bond functionality using an epoxide are shown as an example of the current rhenium-catalyzed deoxygenation protocol. The effect
催化量的Re 2 O 7和亚磷酸三苯酯作为还原剂的组合对于未活化的脂族环氧化物脱氧为烯烃是有效的。该反应在中性条件下与各种取代的环氧化物立体定向进行,并且与各种官能团相容。作为当前rh催化的脱氧方案的实例,显示了使用环氧化物对双键官能团的保护和脱保护。还研究了还原剂对立体选择性的影响,表明使用缺电子的膦或亚磷酸酯是立体特异性脱氧的关键。
Simple protocol for enhanced (E)-selectivity in Julia–Kocienski reaction
作者:Jiří Pospíšil
DOI:10.1016/j.tetlet.2011.02.086
日期:2011.5
A short and efficient Julia-Kocienski olefination protocol, based upon the use of chelating agents (18-crown-6 or TDA-1 for K(+); 12-crown-4 or HMPA for Li(+)), was developed. This protocol enhances the (E)selectivity of the reaction and the desired olefins are obtained generally with >10:1 (E/Z)-selectivity. (C) 2011 Elsevier Ltd. All rights reserved.