Utilization of Aldoses as a Carbonyl Source in Cyclocarbonylation of Enynes

The reaction of enynes with acetyl-masked aldoses in the presence of a rhodium(I) catalyst resulted in cyclocarbonylation, thus avoiding the direct use of carbon monoxide, to afford bicyclic cyclopentenones. In rhodium catalysis, aldoses serve as a carbon monoxide equivalent by donating their carbonyl moieties on the acyclic aldehyde form to enynes. A variety of aldoses, including d-glucose, d-mannose, d-galactose, d-xylose, and d-ribose, can be used as a carbonyl source. Using the method, a wide variety of enynes were cyclocarbonylated in 22−67% yields. An asymmetric variant also proceeded with moderate to high enantioselectivity

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

Facile Preparation of a New BINAP-Based Building Block, 5,5‘-DiiodoBINAP, and Its Synthetic Application

Bis(pyridine)iodonium tetrafluoroborate was successfully used for regioselective iodination of BINAP dioxide to give 5,5‘-diiodoBINAP dioxide in an excellent yield of 92%, with no observed formation of 4,4‘-diiodoBINAP dioxide. A Sonogashira cross-coupling reaction with 5,5‘-diiodoBINAP dioxide gave the desired bis(trimethylsilylethynyl) product in 86% yield. The resulting 5,5‘-disubstituted BINAP dioxides were reduced to the corresponding phosphines, which were used as chiral ligands for rhodium-catalyzed asymmetric 1,4-addition of phenylboronic acid to 2-cyclohexenone to give 3-phenylcyclohexanone in excellent yield with high enantioselectivity

Design and Synthesis of Novel <i>C</i>₂-Symmetric Chiral Piperazines and an Application to Asymmetric Acylation of σ-Symmetric 1,2-Diols

A novel alicyclic chiral C2-symmetric piperazine, (S,S)-7, is designed and synthesized from l-proline. Benzoylation of a series of cyclic and acyclic meso-1,2-diols with a catalytic amount of (S,S)-7 and CuCl2 provided optically active monobenzoates with high enantioselectivity

CO-Transfer Carbonylation Reactions. A Catalytic Pauson−Khand-Type Reaction of Enynes with Aldehydes as a Source of Carbon Monoxide

The reaction of enynes with aldehydes in the presence of a catalytic amount of [RhCl(cod)]2/dppp results in the Pauson−Khand-type reaction without the use of gaseous carbon monoxide to give bicyclic cyclopentenones in high yields (14 examples). Aldehydes serve as a source of carbon monoxide, and their carbonyl moiety is transferred to enynes, resulting in the formation of the carbonylated products. This reaction represents the first example of a CO-transfer carbonylation

Site-Selective Conversion of Azido Groups at Carbonyl α‑Positions to Diazo Groups in Diazido and Triazido Compounds

This paper reports on the selective conversion of alkyl azido groups at the carbonyl α-position to diazo compounds. Through β-elimination of dinitrogen, followed by hydrazone formation/decomposition, α-azidocarbonyl moieties were transformed into α-diazo carbonyl groups in one step. As these reaction conditions do not involve aryl or general alkyl azides, site-selective conversions of di- and triazides were achieved. Through this method, the successive site-selective conjugation of the triazido molecule with three different components is demonstrated

Site-Selective Conversion of Azido Groups at Carbonyl α‑Positions to Diazo Groups in Diazido and Triazido Compounds

This paper reports on the selective conversion of alkyl azido groups at the carbonyl α-position to diazo compounds. Through β-elimination of dinitrogen, followed by hydrazone formation/decomposition, α-azidocarbonyl moieties were transformed into α-diazo carbonyl groups in one step. As these reaction conditions do not involve aryl or general alkyl azides, site-selective conversions of di- and triazides were achieved. Through this method, the successive site-selective conjugation of the triazido molecule with three different components is demonstrated

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

Lewis Acid-Promoted Cyclization Reactions of Alkenyl Ethenetricarboxylates: Stereoselective Synthesis of 2‑Oxotetrahydrofurans and 2‑Oxopyrrolidines

Lewis acid-promoted intramolecular reactions of alkenyl ethenetricarboxylates and the corresponding amides have been examined. Reaction of allyl ethenetricarboxylates and the amides with Lewis acids (1–2 equiv) such as TiCl₄, TiBr₄, AlCl₃, and AlBr₃ gave 3,4-<i>trans</i>-halogenomethyl 2-oxotetrahydrofuran and pyrrolidine derivatives stereoselectively in high yields. The stereochemistries were determined by NOE experiments. Reaction of alkyl-substituted allylic ethenetricarboxylates with Lewis acids gave chloro 2-oxotetrahydrofurans and pyrans. For some alkyl-substituted substrates, cationic intermediates may be formed under the reaction conditions, and rearranged products have been obtained

Lewis Acid-Promoted Cyclization Reactions of Alkenyl Ethenetricarboxylates: Stereoselective Synthesis of 2‑Oxotetrahydrofurans and 2‑Oxopyrrolidines

Lewis acid-promoted intramolecular reactions of alkenyl ethenetricarboxylates and the corresponding amides have been examined. Reaction of allyl ethenetricarboxylates and the amides with Lewis acids (1–2 equiv) such as TiCl₄, TiBr₄, AlCl₃, and AlBr₃ gave 3,4-<i>trans</i>-halogenomethyl 2-oxotetrahydrofuran and pyrrolidine derivatives stereoselectively in high yields. The stereochemistries were determined by NOE experiments. Reaction of alkyl-substituted allylic ethenetricarboxylates with Lewis acids gave chloro 2-oxotetrahydrofurans and pyrans. For some alkyl-substituted substrates, cationic intermediates may be formed under the reaction conditions, and rearranged products have been obtained