Ken-ichi Hirao

Photochemical synthesis of 1,2,3,4-tetrahydroisoquinolin-3-ones from N-chloroacetylbenzylamines

When N-chloroacetyl-3-hydroxybenzylamine (37) in aqueous acetonitrile was irradiated, both ortho and para photocyclizations with reference to the OH group occurred to give 7- and 5-hydroxy-3-oxo-1,2,3,4-tetrahydroisoquinolines (52,53). Similarly, 1-methylisoquinoline derivatives (54,55) were synthesized. N-Chloroacetyl-3,5-dihydroxybenzylamine (39) gave a single photoproduct, 5,7-dihydroxy-3-oxo-1,2,3,4-tetrahydroisoquinoline (56). These photocyclizations were smoothly extended to the synthesis of 1-benzyl, 1-(4′-methoxybenzyl)- and 1-(3′,4′,5′-trimethoxybenzyl)-isoquinoline derivatives (58∼64).

Potential intermediates for syntheses of natural diterpenoids : Syntheses of 10β, 15-epoxy- and 10α, 17-epoxy-enantio-podocarpa-5,7,13-trien-16-oic acid derivatives

Abstract Methyl 10β,15-epoxy-enantiopodocarpa-5,7,13-trien-16-oate(XVIII),methyl10α, 17-epoxy-enantiopodocarpa-5,7,13-trien-16-oate (XIX) and their derivatives were prepared as potential intermediates for syntheses of natural diterpenoids from abietic acid (I).

The baeyer-villiger reaction of strained cage compounds, 1,3-bishomocubanones, via carbocations

Abstract The Baeyer-Villiger oxidation of 1,3-bishomocubanone 1a in chloroform with m-chloroperbenzoic acid (m-CPBA) at room temperature proceeds quite rapidly and gives the ordinary lactone, 10-oxapentacy-clo[5.4.0.02.5.03.9.04.8]undecan-11-one 2a and the skeletal rearrangement product, 11-oxapentacy-clo[6.3.0.02.4.03.7.05.9]undecan-10-one 4a. Methyl substituted homologs (1d, 1e, 1f) of 1a give the corresponding ordinary and rearranged lactones (2d, 2e, 2f, 4d, 4e, 4f). In these oxidations, the mechanism via carbocations, cyclobutyl 18 and cyclopropylcarbinyl cations 19, plays a major role different from the ordinary concerted migration mechanism. Solvent effects, kinetic treatments, and methyl substituent effects on product ratios support this carbocation mechanism. The adduct formation process between a ketone and m-CPBA must be rate-determining.

Fluoroalkylnorbornadienes and their corresponding valence isomer quadricyclanes — a light energy storage system

Abstract As a model for light energy conversion, some fluoroalkylnorbornadienes were prepared using the Diels-Alder reaction between fluoroalkylpropiolates and cyclopentadienes having electron donating substituents (H-, Me-, C 6 H 5 -). Trifluoromethylpropiolate (5) shows the highest reactivity as a dienophile. Esters were converted to ketones which show an intramolecular charge transfer absorption. Irradiation of trifluoromethylnorbornadienes which have a ketonic group using a high pressure Hg lamp quantitatively gave the corresponding quadricyclanes. The later compounds are rather unstable in benzene at room temperature gradually reverting to the original norbornadienes.

Cycloreversion of acylquadricyclane to acylnorbornadiene promoted by metal oxides

The very mild, stable, immobilized, and inexpensive metal oxides effectively catalyzed the cycloreversion of methyl 2,4-dimethyl 6,7-diphenyl-5-propionyltetracyclo[3.2.0.02,−7.04,6] heptan-1-carboxylate (1).

Effect of fluorine substitution of α-and β-hydrogen atoms in ethyl phenylacetate and phenylpropionate on their stereoselective hydrolysis by cultured cancer cells

Abstract ( ±) -Ethyl 2-fluoro-2-phenylacetate was stereoselectively hydrolyzed by cultured cells of several rat cancer cell lines to give the carboxylic acid rich in the R enantiomer. The stereoselectivity increased for ( ±)-ethyl 2-fluoro-2-phenylpropionate ( 2b ) with all present cell lines and for ( ±)-ethyl 2-phenyl-3,3,3-trifluoropropionate (3b) with rat hepatoma McA-RH7777 cell line. The stereoselectivity was different for the different cell lines, as McA-RH7777 cells preferred ( R ) - 2b in contrast with the preference towards ( S ) - 2b by other cells such as ras oncogenetransformed rat liver Anr4 cells. These stereoselectivities were different from those for non-fluorinated ( ±)-ethyl 2-phenylpropionate. Thus fluorine atoms are recognized by ester hydrolases of cancer cells, and fluorine substitution on the acyl group will be useful for making estertype anticancer prodrugs more specific to cancer cells.

New route to 2-substituted indoles by pyrolysis of N-acylacetylphenylhydroxylamines

Convenient and regiospecific synthesis of 2-substituted indol (3) by thermolysis of N-acylacetylphenylhydroxylamine (1 and its mechanism including the formation of a radical intermediate are reported.

Valence isomer interconversion of norbornadienes and quadricyclanes having an acyl group

As a model for light energy conversion, various acylnorbornadienes and their corresponding valence isomers acylquadricyclanes have been prepared. Among these (19) and (31) were found to be the best pair for the purpose because of the visible light absorption of (19), a high quantum yield for its photocycloaddition and a rapid and complete reversion of (31) to (19) with an acid catalyst.

Valence isomerisation between coloured acylnorbornadienes and quadricyclanes as a promising model for visible (solar)light energy conversion

Among many coloured norbornadienes which have been synthesized bearing electron-donating and electron-withdrawing substituents, the 2,3-diphenyl-5-methoxycarbonyl-6-propionly derivative was found to satisfy many important requirements for the chemical conversion of solar light energy because of its visible light absorption, a high quantum yield for its photocycloaddition to the corresponding quadricyclane and a rapid and complete reversion of the quadricyclane to the norbornadiene with an acid catalyst.

Photo-Reimer-Tiemann reaction of phenols, anilines and indolines☆

Abstract The photo-reaction of phenol (1) with chloroform in the presence of diethylamine gave salicylaldehyde (2) and 4-hydroxybenzaldehyde (3) in fair yield. Dihydroxybenzenes, sensitive to alkali, under similar conditions without the base gave corresponding aldehydes and a cyclohexa-2,5-dienone (15). The photo-reaction was also applied to diethylaniline (18), indoline (21) and N-methylindoline (24). In carbon tetrachloride instead of chloroform in an alcohol solution the same type of reaction took place to give esters. The mechanism involving the coupling of a phenoxy radical or a radical cation with dichloromethyl radical and not involving dichlorocarbene is proposed.