Entrainer Effects on Enantiodifferentiating Photocyclization of 5-Hydroxy-1,1-diphenylpentene in Near-Critical and Supercritical Carbon Dioxide

Enantiodifferentiating photocyclization of 5-hydroxy-1,1-diphenyl-1-pentene (<b>1</b>) sensitized by bis­(1,2;4,5-di-<i>O</i>-isopropylidene-α-fructopyranosyl) 1,4-naphthalenedicarboxylate (<b>2</b>) was performed in near-critical and supercritical carbon dioxide media containing organic entrainers to obtain a chiral tetrahydrofuran derivative (<b>3</b>) in enantiomeric excess (ee) higher than those obtained in conventional organic solvents. Interestingly, the entrainer-driven ee enhancement did not depend on the entrainer polarity, which is in contrast to the behavior of the ee observed upon selective solvation in nonpolar organic solvents. This indicates that entrainer clustering around the intervening exciplex is essential in order to keep the intimate sensitizer–substrate contact within the exciplex. Therefore, the clustering itself, rather than its property, is more crucial to prevent the dissociative diffusion to gaseous CO₂. The wider allowance in choosing the entrainer enables us to use more “green” solvents for achieving the ee enhancement, while reducing the environmental risk

Regioselective Rapid Synthesis of Fully Substituted 1,2,3-Triazoles Mediated by Propargyl Cations

Regioselective rapid triazole syntheses at low temperature are described. Organic azides and propargyl cations generated by acids gave fully substituted 1<i>H</i>-1,2,3-triazoles. Most reactions could be performed in 5 min at not only rt but also −90 °C. Both terminal and internal alkynes were acceptable, and the sterically bulky substituents could afford the products smoothly. Various types of three-component coupling reactions were demonstrated, and the presence of allenylaminodiazonium intermediates was indicated

Rh(I)-Catalyzed Asymmetric Synthesis of 3-Substituted Isoindolinones through CO Gas-Free Aminocarbonylation

A highly efficient and accessible synthesis of chiral 3-substituted isoindolinone frameworks is described. The synthesis involved the Rh­(I)-catalyzed asymmetric arylation of boronic acids to 2-halobenzaldimines and the subsequent Rh­(I)-catalyzed intramolecular aminocarbonylation of the resulting 2-halobenzylamines using an aldehyde as the carbonyl source. The method tolerates a variety of functional groups, yielding isoindolinone derivatives in moderate to high yields with high ee-values. In addition, two Rh­(I)-catalyzed transformations could be efficiently accomplished in a one-pot sequence to give chiral isoindolinones by the simple addition of a ligand and an aldehyde after the Rh­(I)-catalyzed asymmetric arylation

Enantiodifferentiating Photoaddition of Alcohols to 1,1-Diphenylpropene in Supercritical Carbon Dioxide: Sudden Jump of Optical Yield at the Critical Density

In the enantiodifferentiating photoaddition of ROH (R = Me, Et, i-Pr) to 1,1-diphenylpropene sensitized by fructosyl 1,4-naphthalenedicarboxylate in supercritical carbon dioxide, the enantiomeric excess of photoadduct increased with increasing bulkiness of the alcohol at all pressures used, with an accompanying sudden jump at the critical density, for which the enhanced clustering of alcohol, particularly in the subcritical pressure region, was revealed to be responsible from the fluorescence spectral examinations

Rh(I)-Catalyzed Asymmetric Synthesis of 3-Substituted Isoindolinones through CO Gas-Free Aminocarbonylation

A highly efficient and accessible synthesis of chiral 3-substituted isoindolinone frameworks is described. The synthesis involved the Rh­(I)-catalyzed asymmetric arylation of boronic acids to 2-halobenzaldimines and the subsequent Rh­(I)-catalyzed intramolecular aminocarbonylation of the resulting 2-halobenzylamines using an aldehyde as the carbonyl source. The method tolerates a variety of functional groups, yielding isoindolinone derivatives in moderate to high yields with high ee-values. In addition, two Rh­(I)-catalyzed transformations could be efficiently accomplished in a one-pot sequence to give chiral isoindolinones by the simple addition of a ligand and an aldehyde after the Rh­(I)-catalyzed asymmetric arylation

Formal [3+2] Cycloaddition of Nitrosoallenes with Carbonyl and Nitrile Compounds to Form Functional Cyclic Nitrones

The synthesis of functional cyclic nitrones via [3+2] cycloadditions of allenamide-derived nitrosoallenes with carbonyl/nitrile compounds, including ketones, esters, and nitriles, is presented herein. Rapid carbon–carbon, carbon–oxygen, and carbon–nitrogen bond formations were achieved with <i>in situ</i> prepared nitrosoallenes, and densely substituted oxacyclic and carbocyclic nitrones containing tetrasubstituted carbon centers were successfully synthesized. The spirocyclic nitrone products synthesized from cyclic dicarbonyl compounds underwent the unique skeletal rearrangements to cyclic α-ketonitrones

Efficient Synthesis of α,β-Unsaturated Alkylimines Performed with Allyl Cations and Azides: Application to the Synthesis of an Ant Venom Alkaloid

An efficient synthesis of α,β-unsaturated alkylimines at low temperature using azides has been developed. Carbocations generated from allyl alcohols helped achieve a rapid conversion under mild conditions with azides to afford reactive α,β-unsaturated imines. Hydroxy or alkoxy groups are essential for these transformations, and utilizing readily accessible allyl alcohols gave a wide extension of substrates. The efficiency of this novel method is demonstrated in the total synthesis of an iminium ant venom alkaloid

Synthesis of α‑Substituted Enoximes with Nucleophiles via Nitrosoallenes

This paper reports nitrosoallene-mediated synthesis of α-substituted enoximes. Nucleophilic substitution of nitrosoallenes, a novel chemical species prepared from allenyl <i>N</i>-hydroxysulfonamides, afforded α-functionalized enoximes. Introduction of various nucleophiles proceeded smoothly to form C–N, C–O, C–S, C–F, and C–C bonds in the presence of azodicarboxylates

Synthesis of α‑Substituted Enoximes with Nucleophiles via Nitrosoallenes

This paper reports nitrosoallene-mediated synthesis of α-substituted enoximes. Nucleophilic substitution of nitrosoallenes, a novel chemical species prepared from allenyl <i>N</i>-hydroxysulfonamides, afforded α-functionalized enoximes. Introduction of various nucleophiles proceeded smoothly to form C–N, C–O, C–S, C–F, and C–C bonds in the presence of azodicarboxylates

Entrainer Effect on Photochirogenesis in Near- and Supercritical Carbon Dioxide: Dramatic Enhancement of Enantioselectivity

Entrainer Effect on Photochirogenesis in Near- and Supercritical Carbon Dioxide: Dramatic Enhancement of Enantioselectivit