Shuki Araki

Regioselective allylation and alkylation of electron-deficient alkenes with organogallium and organoindium reagents

Abstract Triorganogallium and -indium reagents reacted with α,β-unsaturated nitrile and carbonyl compounds to give 1,4-addition products regioselectively. The reaction of allylgallium and allylindium sesquihalides with α,β-unsaturated carbonyl compounds proceeded in a 1,2-addition mode, whereas a 1,4-addition took place with α,β-unsaturated nitriles.

Allylindation of Cyclopropenes in Organic and Aqueous Media: Switching the Regio- and Stereoselectivity Based on the Chelation with a Hydroxyl Group and the Crystal Structure of the Cyclopropylindium Product

Hydroxy-bearing cyclopropenes react with allylindium reagents to undergo clean allylindation both in organic and aqueous media, in which the chelation of the hydroxyl group to indium plays the central role. The regio- and stereoselectivity have been regulated both by the location of the hydroxyl group in the molecules and the reaction solvents. In particular, the allylindation in water shows marked differences from that in organic solvents; the regio- and stereoselectivity have totally been reversed compared with those in organic solvents. Unusually stable cyclopropyl-indium compounds have been isolated from the reaction of 1-(omega-hydroxyalkyl)cyclopropenes and the structure has fully been established by X-ray crystallography.

Control of diastereoselectivity in the crotylation and cinnamylation of aldehydes by the selection of ligands on allylic indium reagents

Diastereoselective couplings of salicylaldehyde, anisaldehyde and 2-pyridylaldehyde with crotyl- and cinnamylindium reagents were studied. The syl/anti selectivity was found to depend largely on the ligands on the indium atom of the allylic indium reagents. A syn-selective cinnamylation of salicylaldehyde was realized by the combination of cinnamyl acetate and indium(I) iodide, whereas an anti-selective coupling with salicylaldehyde was achieved by the indium trichloride/aluminium-mediated cinnamylation.

Stereoselective synthesis of halocyclopropanes via halogenation of cyclopropylindium reagents

A stereoselective synthesis of halocyclopropanes has been achieved via halogenation of the cyclopropylindium reagents prepared from allylindation of cyclopropenes.

Nitrogen‐Rich Mesoionic Compounds from 1,3‐Diaryl‐5‐chlorotetrazolium Salts and Nitrogen Nucleophiles − Synthesis and Properties of 1,3‐Diaryl‐5‐azidotetrazolium Salts

Nitrogen-rich mesoions have been synthesized by the reaction of the 5-chloro-1,3-diaryltetrazolium salt 1 with various nitrogen nucleophiles. The reactions with aqueous ammonia and hydroxylamine gave tripolar mesoionic amide 2 and mesoionic hydroxylamide 4, respectively. N-Substituted and N,N-disubstituted hydrazines yielded the corresponding hydrazides 5, whereas N,N-diphenylhydrazine gave the rearranged product 6. The reaction with sodium azide gave 5-azidotetrazolium salt 8. The azido group of 8 was reduced to give aminotetrazolium salt 9, deprotonation of which yielded the corresponding conjugate base 3. Hard nucleophiles attacked the tetrazolium carbon atom of 8 to give substitution products, whereas soft nucleophiles added the terminal nitrogen atom of the azido group to give addition products. Azidotetrazolium salt 8 reacted further with sodium azide to give a high yield of the tetrazol derivative 11, together with a small amount of triazene 17. The intermediacy of mesoionic carbene 19 is postulated.

CHELATION-CONTROLLED REGIO- AND STEREOSELECTIVE ALLYLINDATION OF NORBORNENOLS

The first allylindation of norbornenol derivatives has been realised highly regio- and stereoselectively. The reactions of allylindium sesquiiodide with syn-bicyclo[2.2.1]hept-2-en-7-ol and endo-bicyclo[2.2.1]hept-5-en-2-ol gave allylated products together with iodinated and oxygenated compounds. The product distribution could be controlled by changing the reaction solvent. In these reactions, the regio- and stereochemistry of the addition of the allylindium reagent is highly regulated via the chelation with the neighbouring hydroxyl group.

A new synthesis of pyrroles by the condensation of cyclopropenes and nitriles mediated by gallium(III) and indium(III) salts

Gallium(III) and indium(III) halides were found to mediate the condensation of cyclopropenes and nitriles to give pyrrole derivatives in moderate yields. When excess nitrile was present, diazepine was also formed.

Nitrogen NMR study of some mesoionic oxadiazoles and thiadiazoles

15N chemical shifts are reported for 10 mesoionic oxadiazoles and thiadiazoles. Some supporting 14N and 13C NMR data are also reported, together with some ab initio molecular orbital calculations and x‐ray diffraction data. The relation between compound structure and 15N chemical shifts is discussed. 14N NMR measurements and ab initio molecular orbital calculations are employed to identify the charge distributions within the molecules studied. Some 1J(C4,C5), 2J(15N,13C) and 1J(15N,13C) spin coupling data for mesoionic oxadiazoles, thiadiazoles and acetylosydnonimines are given. X‐ray diffraction data for the picrate of acetylsydnonimine and a 3,1,2,‐thiadiazole are reported. The bond lengths within the mesoionic backbone are intermediate between the values for single and double bonds, suggesting a conjugated bond system. The arrangement of the exocyclic group observed in the solid state for acetylosydnonimine corresponds to the arrangement predicted by solution NMR studies. Copyright

Ionic TEMPO in Ionic Liquids: Specific Promotion of the Aerobic Oxidation of Alcohols

The main objective of this study was to design a recyclable TEMPO (2,2,6,6‐tetramethylpiperidinyl‐N‐oxyl) derivative that could be used as a catalyst in an ionic liquid solvent for the aerobic oxidation of alcohols by using NaNO2 and HCl as co‐catalysts. To this end, a TEMPO derivative bearing a quaternary ammonium group, [4‐Bu2MeN‐TEMPO][PF6] (1), was prepared. It was subsequently shown that this ionic TEMPO derivative is an efficient catalyst for the aerobic oxidation of a variety of primary and secondary alcohols. It exhibits a synergistic effect with ionic liquid solvents and readily outperforms analogous oxidations in methylene chloride. Moreover, the ionic TEMPO could be recycled five times with no loss of activity.

Synthesis of 3-(phenylazo)-1,2,4-triazoles by a nucleophilic reaction of primary amines with 5-chloro-2,3-diphenyltetrazolium salt via mesoionic 2,3-diphenyltetrazolium-5-aminides.

Summary The reactions of a 5-chloro-2,3-diphenyltetrazolium salt with amines have been examined. In the presence of an inorganic base such as NaHCO3, primary and secondary amines undergo a nucleophilic substitution to give the corresponding 5-aminotetrazolium salts. When triethylamine is used as a base, primary amines give 3-phenylazo-1,2,4-triazoles. A plausible dual-path mechanism is proposed for the formation of the triazoles via Type B mesoionic tetrazolium-5-aminides.