Perfluoro-oxa-alkanoyl peroxides were prepared from the corresponding acyl fluorides and hydrogen peroxide under alkaline condition. The decomposition of these peroxides was found to occur more easily in comparison with those of perfluoroalkanoyl peroxides such as perfluorooctanoyl peroxide. Perfluoro-oxa-alkanoyl peroxides could be used as a reagent for perfluoro-oxa-alkylation of aromatic compound such as benzene, thiophene, furan, or pyrrole, and were found to be applied to direct aromatic perfluoro-oxa-alkylation of polystyrene in the same manner as with perfluoroalkanoyl peroxides. Furthermore, both perfluoro-oxa-alkanoyl peroxides and perfluoroalkanoyl peroxides were shown to be a usuful reagent for the generation of perfluoro-oxa-alkyl and perfluoroalkyl radicals, and to be used for the introduction of perfluoro-oxa-alkyl and perfluoroalkyl groups into monomers possessing lower HOMO energy levels than that of styrene such as vinylsilanes, 3-methacryloxypropylsilane, 3-acryloxypropylsilane, and acrylic acid Especially, perfluoro-ox-a-alkylated aromatic and silicon compounds exhibited excellent surface activity not shown by the perfluoroalkylated ones.
A variety of allylic nitro compounds can be prepared by taking advantage of a unique feature of the nitro group arising from its high electron-withdrawing property. They undergo (i) partial reduction into α, β-unsaturated ketones, aldehydes, or oximes, (ii) replacement of the nitro group by various nucleophiles in the presence of Pd (0) catalyst or stannic chloride, or under solvolysis conditions and (iii) rearrangement of the nitro group or the double bond. Further, 2- (nitromethyl) - and 2- (phenylsulfonylmethyl) -2-cycloalken-1-ones, allylic compounds activated by a keto group, are shown to be readily available and to undergo (i) regioselective SN2 type substitution of the nitro or sulfonyl group by soft nucleophiles via either ionic or radicalchain mechanism, depending on the nature of the nucleophiles and the structure of the substrates, and (ii) eventual SN2' reaction by organocopper reagents and silylated nucleophiles with the aid of trialkylsilyl chloride or triflate and fluoride ion. Chiral 2- (aminomethyl) -2-cycloalken-1-ones, the SN2 products, are utilized for asymmetric synthesis of optically active 3-substituted 2-methylenecycloalkan-1-ones with high enantiomeric excess.
Benzocyclobutene, its homologs, and derivatives are reviewed on the respects of their syntheses, structures, properties, and applications. They are prepared by many methods including cheletropic reaction, ring contraction, 1, 4-dehydrohalogenation, ring closure, cycloaddition to benzyne, aromatization of compounds containing four-membered ring, etc. Upon heating they open the cyclobutene ring to form ο-quinodimethane type diene, which readily undergoes Diets-Alder reaction with a dienophile combined in the reaction system. Cyclobutene ring in these compounds loads strain on the aromatic ring systems, which affects their properties such as basicity, reactivity, etc. These compounds are applied to synthesize many natural products and also make advanced materials such as conductive materials and crosslinking agents. These kind of applications are briefly mentioned.
Ring transformation reaction seems to be one of the important strategies in synthetic chemistry, because it enables otherwise synthetically difficult targets to be accessible by ring transformation from other, readily prepared ring systems. Recently, a novel ring transformation based on aldol condensation followed by acetalization and subsequent Grob fragmentation has been developed by our group. This ring transformation using BF3 etherate/diol such as ethylene glycol seems to be widely applied for the synthesis. In this review, several reaction types of this ring transformation and its application to the synthesis of natural products having the unique skeleton are described.
Recent studies on intramolecular epoxide cyclizations were reviewed. Regio- and stereoselective anionic cyclization of epoxy-nitriles, -olefins, -carbamates and -alcohols were discussed. Also regio- and stereoselective Lewis acid promoted epoxide cyclizations, radical and paradium-catalyzed ones were described.