Computational insight into the mechanism and origin of high regioselectivity in the ring-opening cyclization of spirocyclopropanes with stabilized sulfonium ylides by the DFT

Chromanes with high bioactivity play an important role in nature, and cyclization reactions of cyclopropanes with sulfonium ylides to form chromane skeletons have attracted great attention of scientists. The mechanism as well as origins of regioselectivity and stereoselectivity for the ring-opening/cyclization reactions between cyclohexane-1,3-dione-2-spirocyclopropanes and stabilized sulfonium ylides in CH₂Cl₂ were investigated by using the density functional theory (DFT) M06-2X/6-311+G(d,p)//M06-2X/6-31G(d,p) method combined with the SMD model. The calculated results revealed that the reaction process involved two key steps: the ring-opening step and the cyclization step, with the former being the rate-determining and stereoselectivity-determining step. The regioselectivity of the ring-opening step of spirocyclopropane indicated that the tertiary carbon was more preferential than the secondary one when sulfonium ylide attacked spirocyclopropane. The theoretical results confirmed that the stereoselectivity of the reaction to form the trans-isomer product is more favorable than the cis-isomer, and the calculated trans/cis ratio is in accordance with the experiment. Moreover, the conceptual density functional theory reactivity indices suggest that the electronic effect controls the regioselectivity. What is more, the stereoselectivity analyzed by weak non-covalent interaction also shows the importance of electronic effect. Graphical Abstract.

InCl3: A Versatile Catalyst for Synthesizing a Broad Spectrum of Heterocycles

This review deals with the recent applications of the indium trichloride (InCl₃) catalyst in the synthesis of a broad spectrum of heterocyclic compounds. Over the years, a number of reviews on the applications of InCl₃-catalyzed organic synthesis have appeared in the literature. It is evident that InCl₃ has emerged as a valuable catalyst for a wide range of organic transformations due to its stability when exposed to moisture and also in an aqueous medium. The most attractive feature of this review is the application of the InCl₃ catalyst for synthesizing bioactive heterocyclic compounds. The study of InCl₃-catalyzed organic reactions has high potential and better intriguing aspects, which are anticipated to originate from this field of research.

Intramolecular Umpolung Allylation of Imines

An intramolecular umpolung allylation of imines is reported. This reaction occurs via the intermediacy of 2-azaallyl anions. It could proceed either under transition-metal-catalyzed conditions or under transition-metal-free conditions. Importantly, this approach afforded trans-3-vinyl-4-aminochromanes with high diastereoselectivity, while conventional, nonumpolung methods often display high cis-selectivity.

Asymmetric palladium-catalyzed umpolung cyclization of allylic acetate-aldehyde using formate as a reductant

Asymmetic palladium/chiral diphosphine-catalyzed umpolung cyclization of allylic acetate-aldehyde using formate as a reductant affordscis-disubstituted pyrrolidine, tetrahydrofuran, and spiro carbocycle.

Cooperative titanocene and phosphine catalysis: accelerated C-X activation for the generation of reactive organometallics

The study presented herein describes a reductive transmetalation approach toward the generation of Grignard and organozinc reagents mediated by a titanocene catalyst. This method enables the metalation of functionalized substrates without loss of functional group compatibility. Allyl zinc reagents and allyl, vinyl, and alkyl Grignard reagents were generated in situ and used in the addition to carbonyl substrates to provide the corresponding carbinols in yields up to 99%. It was discovered that phosphine ligands effectively accelerate the reductive transmetalation event to enable the metalation of C-X bonds at temperatures as low as -40 °C. Performing the reactions in the presence of chiral diamines and amino alcohols led to the enantioselective allylation of aldehydes.

Asymmetric synthesis of aminochromanes via intramolecular indium-mediated allylation of chiral hydrazones

The asymmetric intramolecular indium-mediated cyclization reaction delivers chromanes with excellent diastereoselectivity (68-91% yield, dr >99:1). The reaction was efficient for aryl substrates with both electron-withdrawing and -donating groups. Carboxylic acid additives were found to be necessary for optimal reaction.

Inter- and intramolecular palladium-catalyzed allyl cross-coupling reactions using allylindium generated in situ from allyl acetates, indium, and indium trichloride

Inter- and intramolecular palladium-catalyzed allyl cross-coupling reactions using allylindium generated in situ by treatment of allyl acetates with indium and indium trichloride in the presence of Pd(0) catalyst and nBuNMe(2) in DMF were successfully demonstrated. Allylindium species generated in situ by reductive transmetalation of pi-allylpalladium(II) complexes, obtained from a variety of allyl acetates in the presence of Pd(0) catalyst together with indium and indium trichloride, were found to be capable of acting as effective nucleophilic coupling partners in Pd-catalyzed cross-coupling reactions. A variety of allyl acetates such as but-1-en-3-yl acetate, crotyl acetate, and 2-methylallyl acetate afforded the corresponding allylic compounds in good yields in cross-coupling reactions. Various electrophilic cross-coupling partners such as aryl iodides and vinyl bromides and triflates participate in these reactions. Not only intermolecular but also intramolecular Pd-catalyzed cross-coupling reactions work equally well to produce the desired allylic coupling products in good yields.