Diastereoselective Bromocyclization of O-Allyl-N-tosyl-hydroxylamines
摘要:
The intramolecular bromoamination of O-allyl-N-tosyl-hydroxylamines results in the formation of isoxazolidines via selective 5-endo-tet cyclization. This process occurs trans-selectively in high yield and diastereoselectivity. The obtained bromo-isoxazolidines provide access to other useful building blocks, such as 2-azido-aminoalcohols, diaminoalcohols, and aziridines.
Enantioselective Synthesis of <i>trans</i>-Aryl- and -Heteroaryl-Substituted Cyclopropylboronates by Copper(I)-Catalyzed Reactions of Allylic Phosphates with a Diboron Derivative
作者:Chongmin Zhong、Shun Kunii、Yuki Kosaka、Masaya Sawamura、Hajime Ito
DOI:10.1021/ja103783p
日期:2010.8.25
A new asymmetric route for the synthesis of trans-2-aryl- and -heteroaryl-substituted cyclopropylboronates has been developed. (Z)-3-arylallylic phosphates were converted to the opticallyactive products with high yield and diastereo- and enantioselectivitythrough a copper(I)-catalyzed reaction with a diboron derivative. Under mild reaction conditions, the reaction affords the arylcyclopropane products
A copper catalyst generated in situ from widely available copper salt and imidazolium salt in the presence of t-BuOK showed high efficiency for the semihydrogenation of a wide range of internal and terminal alkynes to their corresponding alkenes without obvious over-reduction. Functional groups, such as hydroxyl, nitro, halides, and amino, etc. were tolerated. The Z/E ratios of the obtained alkenes were generally >99%. Finally, semireduction of bulky alkynes also went smoothly. (C) 2014 Elsevier Ltd. All rights reserved.