Masatomi Ohno

Fullerene glycoconjugates: A general synthetic approach via cycloaddition of per-O-acetyl glycosyl azides to [60]fullerene

Abstract A general synthetic way to incorporate oligosaccharides into [60]fullerene via cycloadditon and deacetylation is presented. The cycloaddition reaction in refluxing chlorobenzene gave a mixture of two unseparable stereoisomers of N-β-glycopyranosyl [5,6]-azafulleroids in 13∼28% yields for per-O-acetyl glycosyl azide of d -glucopyranose, d -galactopyranose, lactose, maltose, and maltotriose.

An efficient functionalization of [60]fullerene. Diels-Alder reaction using 1,3-butadienes substituted with electron-withdrawing and electron-donating (silyloxy) groups

Abstract The Diels-Alder strategy was found suitable for the functionalization of C 60 using 1,3-butadienes substituted with an electron-withdrawing group as well as with an electron-donating group, giving cyclohexene-fused C 60 derivatives having ethoxycarbonyl, acetyl, cyano, phenylsulfonyl and nitro substituents. These cycloadducts were stabilized by conjugation with the substituent and no cycloreversion took place. Though the dienes are electron-deficient in nature, the HOMO (diene) - LUMO (C 60 ) interaction was significant as indicated by PM3 calculations.

Hetero-diels-alder reaction of fullerene: Synthesis of thiochroman-fused C60 with o-thioquinone methide and oxidation to its S-oxides

Cycloaddition reaction of C60 with o-thioquinone methide afforded a thiochroman-fused C60 derivative, using benzothiet as a precursor. The cycloadduct was further oxidized with mCPBA to the corresponding sulfoxide and sulfone. However, the self-sensitized photooxygenation to the sulfoxide was unsuccessful.

The first 1,3-dipolar cycloaddition reaction of [60]fullerene with thiocarbonyl ylide

Abstract A thiocarbonyl ylide generated by sila -Pummerer rearrangement of bis(trimethylsilylmethyl) sulfoxide reacted with C 60 to give a tetrahydrothiophene-fused C 60 derivative. The cycloadduct was readily oxidized with mCPBA to give the corresponding sulfoxide and fulfone derivatives, which are useful for further functionalization.

Diverse process in [4+2]cycloaddition reaction of silyl enol ethers of N-substituted 2-acetylpyrroles to an indole skeleton

Abstract The title reaction occurred with the diverse rearomatization process depending on the N -substituent: Air oxidation ( N -ethoxycarbonyl), elimination of PhSO 2 and Me 3 Si groups ( N -phenylsulfonyl), or ene reaction with another dienophile ( N -methyl).

Synthesis of heterocycle-linked [60]fullerene derivatives by heterocyclic o-quinodimethane Diels-Alder reaction and self-sensitized photooxygenation of the cycloadducts

[60]Fullerene underwent [4+2]cycloaddition reaction smoothly with heteroaromatic analogs of o-quinodimethanes including furan, thiophene, oxazole, thiazole, indole and quinoxaline to give the corresponding heterocycle-linked [60]fullerenes. Among them, the furan and oxazole derivatives were prepared with all equipments covered with an aluminum foil, because of lability to oxygen under exposure to room and sun lights. Intended self-sensitized photooxygenation afforded epoxy-γ-lactone from the former and diester from the latter after methanolysis and hydrolysis.

Ring transformation of 4-acylmethyl-2-chloro-4-hydroxy-2-cyclobutenone to γ-acylmethylenetetronate by thermal rearrangement: New synthetic aspect of squaric acid as a C4-synthon

Title cyclobutenones prepared from the TiCl4-catalyzed addition of a silyl enol ether to squaric acid dichloride and ester chloride were subjected to thermolysis (reflux in an aromatic solvent), and γ -acylmethylenetetronates were obtained stereoselectively with (Z)-geometry via an α,β unsaturated chloroketene intermediate. The mechanism, application of this novel rearrangement to synthesis of basidalin and related photolysis were described.

Base-catalysed oxidative [3 + 2]cycloaddition reaction of [60]fullerene with β-dicarbonyl compounds

The ambiphilic nature of β-keto esters and β-diketones allows cycloaddition to C60 in the presence of piperidine to give dihydrofuran-fused C60 derivatives via oxidative cyclization complimentary to the concerted process.

Synthesis and 1,3-dipolar cycloaddition reaction of homoadamantane-incorporated nitrones and rearrangement of the cycloadducts to homoadamantane-fused pyrroles

Abstract The bridging nitrones 7, 8 incorporated in a homoadamantane ring system were obtained by oxidation of 4-azahomoadamantane 5, 6 with SeO2/H2O2. The 1,3-dipolar cycloaddition reaction of these nitrones with the electron-deficient alkynes proceeded regiospecifically at 0 °C-r. t. to give 4-substituted isoxazolines. The reaction with phenylacetylene required forced conditions, where 5-substituted isoxazoline 9d was obtained from 7 using the dipolarophile as a solvent, and rearranged pyrrole 12d was formed directly from 8 at a higher reaction temperature. The resulted cycloadducts from ketonitrone 8 were further converted to homoadamantane-fused pyrroles. In this case, 2-substituted and 3-substituted pyrroles 12a and 12e were obtained respectively from the same starting material via the different mechanism. The former arose via an acylaziridine route by thermolysis and the latter via an enamine route in protic solvents.

Synthesis of squaric acid derivatives by Lewis acid-catalysed reaction of its dichloride, methyl ester chloride, diethylamide chloride, and ethyl diester with unsaturated organosilanes: new method for C–C bond formation on cyclobutenedione

The squaric acid family of derivatives, e.g. dichloride 2, methyl ester chloride 3, diethyl amide chloride 4, and ethyl diester 5, reacted with a variety of unsaturated organosilanes 6 in the presence of a catalyst, typically titanium tetrachloride, at –78 to 0 °C to give addition products (e.g., 7, 9, 11) and/or substitution products (e.g., 8, 10, 12, 13) after dechlorosilylation either via 1,2- or 1,4-addition. The mode of addition depended on the nature of the acid family and on the substitution pattern of the organosilane. The former product predominated in the reaction of the chlorides 2–4 with all silyl ketene ketals used, and with some allylsilanes and silyl enol ethers unless the reactive site (γ to a silyl group) of these silanes was more crowded, whereas the diester 5 gave rise to the latter product 13 irrespective of the substitution pattern. In some cases, catalyst and reaction temperature also affected the mode of addition. The reactivity was found to be in the order 2 > 3 > 4, being reflected in the reaction temperature.