Pyrone Diels-Alder Routes to Indolines and Hydroindolines: Syntheses of Gracilamine, Mesembrine, and Δ<sup>7</sup>-Mesembrenone
作者:Pei Gan、Myles W. Smith、Nathaniel R. Braffman、Scott A. Snyder
DOI:10.1002/anie.201510520
日期:2016.3.7
Although the Diels–Alder reaction has long been utilized for the preparation of numerous heterocycles, opportunities to extend its power remain. Herein, we detail a simple, modular, and robust approach that combines various amines regioselectively with 4,6‐dichloropyrone to create substrates which, under appropriate conditions, can directly deliver varied indolines and hydroindolines through [4+2]
Metal cation-exchanged montmorillonite (M
n+
-mont)
works in acetonitrile at 80 °C as a Lewis acid catalyst for
the intermolecular carbonyl-ene reaction of
α-methylstyrenes with paraformaldehyde to give the
corresponding homoallylic alcohols, Zr
4+
-mont being the most
effective of the many M
n+
-mont catalysts examined.
Similarly, the catalyst is also useful for the highly stereoselective
intramolecular cyclization of citronellals to afford isopulegols, the
reaction being much faster. Regeneration of the catalyst is confirmed
for Zr
4+
-mont, which can be effectively recycled at least
five times.
Directly opposing Keulemans rule! Phosphinites work as reversiblybounddirectinggroups allowing for the first highly regioselective hydroformylation of 3‐substituted homoallylic alcohols to construct quaternary carbon centers. This method enables the atom‐economical synthesis of a wide range of α,α‐disubstituted γ‐lactones and highly substituted tetrahydrofurans (see scheme; R1, R2=alkyl/aryl).
直接反对Keulemans统治!次膦酸盐作为可逆结合的导向基团起作用,从而允许3-取代均烯丙基醇的首次高度区域选择性加氢甲酰化以构建季碳中心。该方法可实现多种α,α-二取代的γ-内酯和高度取代的四氢呋喃的原子经济合成(参见方案; R 1,R 2 =烷基/芳基)。
Rhodium-Catalyzed Diverse Arylation of 2,5-Dihydrofuran: Controllable Divergent Synthesis via Four Pathways
The rhodium-catalyzed controllable diverse arylation of 2,5-dihydrofuran with arylboronic acids is reported. By fine-tuning of the reaction conditions, four different ring-opening or oxidative arylation pathways are controlled in the rhodium-catalyzedarylation of 2,5-dihydrofuran, granting selective access to 2-aryl or 3-aryl homoallylic alcohols and 3-aryl or 4-aryl-2,3-dihydrofurans. The catalytic
homoallyl sulfones were prepared from homoallyl alcohols, which are easily accessible through the recently reported Lewis acid isomerization of oxetanes. The iridium-catalyzed asymmetric hydrogenation of homoallylic sulfones afforded γ-chiral sulfones with excellent enantioselectivities (up to 98% ee). The synthetic potential of this novel methodology was demonstrated by the total synthesis of (R)-(−)-curcumene
报道了一种制备手性甲基苄基化合物的新方法。末端高烯丙基砜是由高烯丙醇制备的,可以通过最近报道的氧杂环丁烷的路易斯酸异构化轻松获得。铱催化的高烯丙基砜的不对称氢化提供了具有优异对映选择性(高达 98% ee)的 γ-手性砜。 ( R )-(−)-姜黄烯的全合成证明了这种新颖方法的合成潜力。