Regiochemical control of the ring opening of 1,2-epoxides by means of chelating processes. 5. Synthesis and reactions of some 2,3-epoxy-1-alkanol derivatives
摘要:
In order to study the effect of a remote polar functionality on the regiochemistry of the ring opening of aliphatic epoxides, the synthesis and some nucleophilic additions (methanolysis, azidolysis, and aminolysis) of suitable 2,3-epoxy-1-alkanol derivatives (epoxides trans-1a-d and cis-2) were carried out. The C-3 selectivity commonly observed when nonchelating ring opening conditions are used is lower than when the epoxides are allowed to react in the presence of metal ions (Li+, Mg2+, Zn2+) due to the probable intervention of bidentate-chelated intermediates in the latter case, and in some instances an almost complete C-3 regioselection is obtained. Under identical conditions involving chelation control, trans epoxide la shows higher C-3 selectivity than cis isomer 2. A free hydroxyl functionality is not necessary in order to observe chelation-controlled regioselectivity in the epoxides that we examined.
Allylic Etherification via Ir(I)/Zn(II) Bimetallic Catalysis
作者:Justin P. Roberts、Chulbom Lee
DOI:10.1021/ol0508328
日期:2005.6.1
[reaction: see text] An efficient allylic etherification of aliphatic alcohols with allylic carbonates has been achieved by an iridium catalysis using stoichiometric zinc alkoxides or a two-component bimetallic catalytic system where the Ir(I) catalyst acts on allylic carbonates to generate electrophiles while aliphatic alcohols are separately activated by Zn(II) coordination to function as nucleophilies
Arabinose-Derived Ketones as Catalysts for Asymmetric Epoxidation of Alkenes
作者:Tony K. M. Shing、Gulice Y. C. Leung、To Luk
DOI:10.1021/jo050928f
日期:2005.9.1
Readily available arabinose-derived ketones, containing a tunable butane-2,3-diacetal as the steric blocker, displayed increasing enantioselectivity (up to 90% ee) with the size of the acetal alkyl group in catalytic asymmetricepoxidation of trans-disubstituted and trisubstituted alkenes. The stereochemical communication between our ketonecatalysts and the alkene substrates is mainly due to steric
Diastereoselective Borocyclopropanation of Allylic Ethers Using a Boromethylzinc Carbenoid
作者:Guillaume Benoit、André B. Charette
DOI:10.1021/jacs.6b09090
日期:2017.2.1
borocyclopropanation of (E)- and (Z)-allylic ethers and styrene derivatives via the Simmons-Smith reaction using a novel boromethylzinc carbenoid is described. The carbenoid precursor is prepared via a 3-step sequence from inexpensive and commercially available starting materials. This methodology allows for the preparation of 1,2,3-substituted borocyclopropanes in high yields and diastereoselectivities
Iridium‐catalyzed hydroarylation of alkenyl ethers, such as allylic and homoallylic ethers, by C−H bond activation gave high yields of the corresponding addition products, where the aryl groups were selectively installed at the α‐carbon atom to the alkoxy group. The reaction involves an isomerization of the alkenyl ethers into the corresponding 1‐alkenyl ethers, which then undergo the regio‐ and enantioselective
<i>Z</i>-Selective alkyne semi-hydrogenation catalysed by piano-stool <i>N</i>-heterocyclic carbene iron complexes
作者:Chloe Johnson、Martin Albrecht
DOI:10.1039/c8cy00681d
日期:——
NHC iron(II) piano-stoolcomplexes catalyse the selective semi-hydrogenation of alkynes to alkenes using silanes as reducing agents. Aromatic terminal alkynes are converted to styrenes without over-reduction to ethylbenzene derivatives. Furthermore, internal aryl alkynes afford cis-alkenes with excellent Z-selectivity.