Reactions of a Ga/P‐Based Frustrated Lewis Pair with HX (X = F – I), Heterocumulenes R–NCY (Y = O,S) and Chalcogens–Adduct Formation and Surprising Stability towards Protolysis

Treatment of the geminal Ga/P‐based frustrated Lewis pair (FLP) Mes₂P–C(GatBu₂)=C(H)–Ph ( 1 ) with HX (X = F, Cl, Br, I) afforded the corresponding adducts 2 with the protons bound to the P and the halide anions coordinated to the Ga atoms. Short intramolecular contacts may indicate P–H ··· X hydrogen bonding interactions. The Br and I compounds ( 2c , 2d ) were accessible in moderate yields even when aqueous solutions of the acids were employed. These unexpected reactions confirm the surprising stability of FLP 1 towards protolysis. Heterocumulenes R–N=C=Y (Y = O, S) and 1 yielded adducts with two different structural motifs. The N=C=Y groups were coordinated to the FLP either via the C=Y (Y = S; Ph–N=C=O) or the C=N bonds (Ph–N=C=O, Et–N=C=O). For phenyl isocyanate the C=O bonded isomer was observed in the solid state, while both isomeric forms were detected in solution. Steric shielding and the hardness of the atoms may influence the formation of the respective isomer. Cleavage of the C=S bonds of isothiocyanates was observed for the first time and afforded a sulfur adduct 9a , in which an S atom (electron sextet) was bound to the lone pair of electrons at phosphorus and to the Lewis acidic Ga atom. Four‐membered PCGaY heterocycles resulted, which were also synthesized in high yields by the direct reaction of 1 with propylene sulfide or selenium.     

分子内孤对(n)轨道间相互作用的又一例证——某些杂氮环已烷系列化合物的气相HeIα紫外光电子能谱(UPS)研究

Ione pair orbital and their interaction in some nitrogen heterocyclic compound series have been interpreted in terms of through-space and through-bond mechanisms through the study of their gas phase ultraviolet photoelectron spectrocopy. The HAM/3 molecular orbital calculations on each molecule of the studied series were also carried out. The order of experimental vertical ionization potentials of the molecules can be not only predicated, but the spacing of through-space and through-bond interactions splitting of the studied compounds are consistent with the results of HAM/3 calculations.     

Design and Application of m-Hydroxybenzyl Alcohols in Regioselective (3 + 3) Cycloadditions of 2-Indolymethanols†

A new class of m-hydroxybenzyl alcohols has been designed as competent three-carbon building blocks and achieved their application in 2-indolylmethanol-involved regioselective (3 + 3) cycloadditions under the catalysis of Brønsted acids. By this appoach, a series of indole-fused six-membered cycloadducts have been synthesized in overall good yields (up to 98%) with excellent regioselectivity (all >95: 5 rr), thus affording a powerful method for the construction of indole-fused six-membered rings. Moreover, a catalytic asymmetric version of this (3 + 3) cycloaddition has been preliminarily investigated, which revealed the potential of the reaction for constructing chiral indole-fused six-membered rings in an enantioselective manner. This work not only has accomplished the first design of m-hydroxybenzyl alcohols as competent reactants, but also represents the first application of m-hydroxybenzyl alcohols as three-carbon building blocks in cycloadditions. In addition, this work provides a good example for regioselective and C3-nucleophilic (3 + 3) cycloadditions of 2-indolylmethanols, which will substantially enrich the chemistry of 2-indolylmethanols.     

An Enantioselective Approach to Heteroatom-Containing Bicyclic Derivatives via Inverse-Electron-Demand Diels−Alder Reactions

Chiral heteroatom-containing bicyclic scaffolds are important pharmacophores and prevalent in bioactive natural products and drug molecules. Herein, we report a unified approach for the divergent synthesis of chiral heteroatom-containing bicyclic derivatives by lanthanide (III)-catalyzed asymmetric inverse-electron-demand Diels–Alder reactions of 2-pyrones. These reactions occur with various readily available dihydropyrroles and dihydrofurans as dienophiles, providing a step-economical synthetic platform for densely functionalized cis-hydroindoles and cis-hydrobenzofurans with excellent yields and enantioselectivities. The synthetic utility of this approach is demonstrated by the concise synthesis of (–)-α-lycorane and (–)-lycorine alkaloids.