The highly enantioselective Diels–Alderreaction of acetylenic dienophiles is shown to be effectively catalyzed by cationic chiral palladium complexes. Not only the degree but also the sense of enantioselectivity critically depends on the steric demand of ligands. Computational analyses indicate that the steric demand does not affect the endo/exo‐selectivity but the enantioface selectivity of dienes
Asymmetric “Acetylenic” [3+2] Cycloaddition of Nitrones Catalyzed by Cationic Chiral Pd<sup>II</sup>
Lewis Acid
作者:Kazuya Honda、Koichi Mikami
DOI:10.1002/asia.201801016
日期:2018.10.4
Highly enantioselective [3+2] cycloaddition of ynones and nitrones has been developed. Very bulky ligand, DTBM‐SEGPHOS, was used for an effective asymmetric induction over distal reaction centers on the linear ynone dipolarophile and for prevention of PdII catalyst deactivation by coordination of the nitrones. The reaction has wide scope of substrates in both ynones and nitrones.
Synthesis of tetrasubstituted pyridines by the acid-catalysed Bohlmann–Rahtz reaction
作者:Mark C. Bagley、Christian Brace、James W. Dale、Maren Ohnesorge、Nathan G. Phillips、Xin Xiong、Justin Bower
DOI:10.1039/b203397f
日期:2002.7.11
New facile experimental procedures for the preparation of 2,3,4,6-tetrasubstituted pyridines in a single synthetic step have been developed. Thus, an enamino ester and alkynone react by Michael additionâcyclodehydration in a heterocyclisation process that is catalysed by acetic acid, Amberlyst 15 ion exchange resin, zinc(II) bromide or ytterbium(III) triflate. The new one-step Brønsted or Lewis acid-catalysed BohlmannâRahtz reaction is a simple, direct and highly expedient method for the synthesis of pyridines that proceeds at a lower reaction temperature and avoids the need to isolate reaction intermediates.
One or Two-Step Bohlmann-Rahtz Heteroannulation of 6-Aminouracil Derivatives for the Synthesis of Pyrido[2,3-<i>d</i>]pyrimidines
作者:Mark C. Bagley、David D. Hughes
DOI:10.1055/s-2002-32953
日期:——
The Michael addition-cyclodehydration of a 6-aminouracil and alkynone proceeds to give 5-deazapterin derivatives with total control of regiochemistry. This simple and facile cyclocondensation process is catalyzed by zinc(II) bromide or ytterbium(III) trifluoromethanesulfonate at 110 °C, providing the heteroannulated products in up to 94% yield.
6-氨基尿嘧啶和炔酮的迈克尔加成环脱水反应得到完全控制区域化学的5-去氮杂蝶呤衍生物。这种简单易行的环缩合反应由溴化锌 (II) 或三氟甲磺酸镱 (III) 在 110 °C 催化,以高达 94% 的产率提供杂环化产物。
Synthesis of tetrasubstituted thiophenes from pyridinium 1,4-zwitterionic thiolates and modified activated alkynes
affording various tetrasubstituted thiophenes with aryl, alkenyl, alkyl, or silylgroup at the special position. The structural modification of alkyne substrates enabled the synthesis of diverse thiophenes to be achieved using the pyridinium 1,4-zwitterionic thiolates as the sulfur-containing building blocks. This approach is metal-free and catalyst-free.