Michikazu Yoshioka

Stepwise oxidation of the stannole dianion.

Tin oxidation of stannole dianion 1 with 1.3 equivalents of oxygen gave terstannole-1,3-dianion 3. The non-aromatic nature of 3 was confirmed by X-ray crystallographic analysis. Treatment of 1 with 1,2-dibromoethane (3 equiv) gave poly(1,1-stannole) 4, the formation of which was proven by reduction of 4 with lithium to revert to the starting dianion 1. Reaction of 1 with 1,2-dibromoethane (3 equiv) in the presence of phenyllithium gave phenyl-capped ter(1,1-stannole) 7. The electronic absorption spectra of newly obtained stannoles were also measured.

Photocyclization of (ω-dialkylamino)alkyl β-oxoesters via remote hydrogen transfer

The (ω-dialkylamino)alkyl β-oxoesters (1) undergo photocyclization via remote hydrogen transfer to give the medium-sized azalactones (2) and/or aminolactones (3). Intramolecular electron transfer from nitrogen to the excited carbonyl group of (1) occurs prior to the remote hydrogen transfer.

Type II photoreactions of α-alkyl β-oxoesters. Neighboring group effect on 1,4-biradical reactions and effective internal filter effect by the type II photoproduct

Abstract The α-alkyl β-oxoesters 1 undergo type II photoreactions. The process of back hydrogen transfer in the 1,4-biradical intermediate to revert to the starting ester is suppressed because of the intramolecular hydrogen bonding between the hydroxyl and carboalkoxyl groups in the biradical intermediate. The hydrogen bonding determines the stereochemistry of 1,4-biradical cyclization. The cyclobutanols having the hydroxyl group cis to the carboalkoxyl group are formed exclusively from the α-alkyl β-oxoesters 1 . The enol form of the type II elimination product, the benzoylacetate 2 , acts as an effective internal filter for the photoreaction of the α-alkyl β-oxoester 1 .

SIMPLE METHOD FOR THE SYNTHESIS OF STANNOLE DIANION

Reduction of 1-t-butyl-1,2,3,4,5-pentaphenylstannole by lithium gave the stannole dianion. Reduction of the bi(1,1-stannole) having a t-butyl group on the tin by lithium also gave the stannole dianion, the formation of which was evidenced by spectral analysis and chemical trapping reaction.

Unusual substituent effect by the α-acetyl group on the type II photoreaction of valerophenones : strong wavelength dependence of quantum yields

Abstract α-Acetyl-γ-methylvalerophenone ( 1a ) and α-acetylvalerophenone ( 1b ) show wavelength-dependent type II photoreactivity. Their quantum yields of disappearance are 0.01 at 313 nm and unity at 366 nm. The wavelength dependence was analysed on the basis of the kinetics by considering the internal filter effect caused by the enol form of both the product and the starting material. The enol form of the starting material was found to play a much more important role in the wavelength dependence than the endol form of the product. α-Acetylα-methylvalerophenone ( 1c ), which has no enolizable hydrogen, also undergoes the type II reaction. However, the quantum yields for the disappearance of 1c are low at both 313 and 366 nm. This is probably due to the effective reverse hydrogen transfer to yield the ground state starting material from the 1,4-biradical intermediate or the effective recombination of radicals produced via rapid α cleavage.

Reaction of singlet oxygen with enolic tautomers of β-dicarbonyls. α-hydroxylation of 2-acyl- and 2-carboalkoxy-3,4-dihydronaphthalen-1(2H)-ones

Abstract Dye-sensitized photooxidation of enolic tautomers of naphthalenones (5) gave hydroperoxynaphthalenones (6) and naphthols (7). Deoxygenation of 6 by triphenylphosphine gave hydroxynaphthalenones (8).

Type I and type II photochemical reaction of ω-isobutyryl-ω-methyl-2,3-benzocycloalk-2-en-1-ones

Abstract ω-Isobutyryl-ω-methyl-2,3-benzocycloalk-2-en-l-ones. (6a-c) undergo both type I and type II photoreactions. The type I/type II product ratio depends on the ring size; the six-membered ketone 6a is subject to type II reaction and the eight-membered ketone 6c is subject to type I reaction predominantly. The cyclization/elimination ratio of the type II reaction of 6 also depends on the ring size; the ratio decreases with increasing ring size.

Photochemical reaction of 3-hydroxy-1-(o-methylaryl)alkan-1-ones: formation of cyclopropane-1,2-diols and benzocyclobutenols through β- and γ-hydrogen abstractions

Irradiation of 3-hydroxy-2,2-dimethyl-1-(o-methylaryl)-alkan-1-ones 1a–h having a bulky alkyl group or an aryl group on C-3 in methanol gave trans- and cis-cyclopropane-1,2-diols 2a–g and 3a, c–f, h and benzocyclobutenols 4a–h through β- and γ-hydrogen abstractions. Irradiation of 3-hydroxy-2,2-dimethyl-1-(o-methylphenyl)-alkan-1-ones 1i–k having ethyl, methyl or no substituent at C-3 gave benzocyclobutenols 4i–k and 1,3-diketones 5i, j, but no cyclopropane-1,2-diols. The cyclopropane-1,2-diols were sensitive to air and readily oxidized to the corresponding 1,3-diketones. Irradiation of 3-hydroxy-4,4-dimethyl-1-(o-methylaryl)pentan-1-ones 8a, b having a methyl group or no substituent on C-2 gave benzocyclobutenols 9a, b, the peroxide 10 and phthalides 11a, b. 3-Hydroxy-2,2-dimethyl-1,3-diphenylpropan-1-one 12a and 3-hydroxy-2,2,4-trimethylpentan-1-one 12b also underwent photocyclization through β-hydrogen abstraction to give cyclopropane-1,2-diols 13a, b and 14.

Photochemical reaction of β-hydroxyketones. Formation of cyclopropane-1,2-diols

Irradiation of 3-hydroxy-1-(o-methylaryl)-2,2,4-trimethylpentan-1-ones 1 in methanol gave cyclopropane-1,2-diols 2, 1,3-diketones 3 and benzocylobutenols 4.

Reaction of singlet oxygen with enolic tautomers of 1-aryl-2-methyl 1,3-diketones

The 1-(2′,4′,6′-trialkylphenyl)-2-methyl 1,3-diketones 6 exist in the enol form in solution, and on reaction with singlet oxygen in acetonitrile give products arising from hydrogen abstraction from both the enolic hydroxy and the 2-methyl groups by the singlet oxygen; namely, the 2-hydroperoxy 1,3-diketones 7, the 2-methylene 1,3-diketones 8 and the epoxy ketones 9. The 2-hydroperoxy 1,3-diketones 7 readily undergo deoxygenation by triphenylphosphine to give the 2-hydroxy 1,3-diketones 12. In the reaction of 6 in methanol or ethanol, the initially formed enedione 8 reacts with the solvent to give the corresponding Michael adducts 10 and 11.