Unique Reactivity of anti- and syn-Acetoxypyranones en Route to Oxidopyrylium Intermediates Leading to a Cascade Process
摘要:
Unique reactivity of anti- and syn-acetoxypyranones was observed in oxidopyrylium-alkene [5 + 2] cycloadditions. The subtle interplay between the corresponding acetoxypyranone conformation and steric bulk of tertiary amine bases causes syn-acetoxypyranones to undergo [5 + 2] cycloaddition appreciably faster than anti-acetoxypyranones. Additionally, the efficiency of a cascade process that afforded a novel tetracyclic lactol was determined to be dependent on the relative stereochemistry of each diastereomer, the amine base utilized, and the addition of water.
Enantioselective Organo-Photocatalysis Mediated by Atropisomeric Thiourea Derivatives
作者:Nandini Vallavoju、Sermadurai Selvakumar、Steffen Jockusch、Mukund P. Sibi、Jayaraman Sivaguru
DOI:10.1002/anie.201310940
日期:2014.5.26
this, organo‐photocatalysts that are based on atropisomericthioureas and display lower excited‐state energies than the reactive substrates have been developed. These photocatalysts were found to be efficient in promoting the [2+2] photocycloaddition of 4‐alkenyl‐substituted coumarins, which led to the corresponding products with high enantioselectivity (77–96 % ee) at low catalyst loading (1–10 mol %)
Direct Access to Versatile Electrophiles via Catalytic Oxidative Cyanation of Alkenes
作者:De-Wei Gao、Ekaterina V. Vinogradova、Sri Krishna Nimmagadda、Jose M. Medina、Yiyang Xiao、Radu M. Suciu、Benjamin F. Cravatt、Keary M. Engle
DOI:10.1021/jacs.8b03704
日期:2018.7.5
discovery. Reactions that directly transform inexpensive chemical feedstocks into versatile carbon electrophiles would therefore be highly enabling. Herein, we report the catalytic, regioselective oxidative cyanation of conjugated and nonconjugated alkenes using a homogeneous copper catalyst and a bystanding N-F oxidant to furnish branched alkenyl nitriles that are difficult to prepare using existing methods
REACTIONS OF ORGANOALUMINUMS WITH COPPER(II) HALIDES. A CONVENIENT ROUTE TO ALKYL HALIDES PROM OLEFINS VIA HYDROALUMINATION
作者:Fumie Sato、Yoshikuni Mori、Masao Sato
DOI:10.1246/cl.1978.833
日期:1978.8.5
The reaction of lithium tetraalkylaluminums with copper(ll) chloride or bromide gives the corresponding alkyl halides in good yield. The facile reaction offers a convenient method for the preparation of 1-haloalkanes or 1-haloalkenes from 1-alkenes or nonconjugated diolefins, respectively.
Alk-4-enyl bromides and iodides 1, when treated with the tributyltin hydride/CO system, undergo carbonylative cyclisation to give Cyclopentanones in good yields (AIBN cat., benzene, 75–90 atm, [1]= 0.025–0.05 mol dm–3, 80 °C, 2–3 h).
A potentially general method to control relative stereochemistry in enone–olefin 2+2-photocycloaddition reactions by using eniminium salt surrogates
作者:Xiaolu Cai、Virginia Chang、Chuanfeng Chen、Hyun-Jin Kim、Patrick S Mariano
DOI:10.1016/s0040-4039(00)01581-1
日期:2000.12
A new strategy to control the stereochemistry of enone–olefin2+2-photocycloaddition reactions, based on the use of eniminium salt surrogates, is experimentally tested. In contrast to enone–olefinphotocycloadditions, which emanate from enone triplet excited states and follow non-concerted pathways, analogous reactions of conjugated eniminium salts can occur by singlet, concerted routes and, as a result