Michael Orfanopoulos

Acyl Radical Reactions in Fullerene Chemistry: Direct Acylation of [60]Fullerene through an Efficient Decatungstate-Photomediated Approach

A versatile and highly efficient photochemical methodology for the direct acylation of C(60) has been developed. This approach utilizes a wide variety of acyl radicals derived from aldehydes through a hydrogen atom abstraction process mediated by tetrabutylammonium decatungstate [(n-Bu(4)N)(4)W(10)O(32)]. The single addition reaction of these acyl radicals to [60]fullerene proceeded selectively to afford a novel class of previously unexplored fullerene-based materials. Product analysis of this reaction showed that decarbonylation and acylation pathways compete when a tertiary or phenylacetyl aldehyde is the starting material. However, a decrease of the reaction temperature was found to be effective in overcoming the decarbonylation encountered in certain acyl radical additions to C(60); the carbonyl radical addition precedes decarbonylation even in the cases where the decarbonylation rate constant exceeds 10(6) s(-1) (i.e., phenylacetaldehyde). The regiochemistry of the t-butyl radical addition was also found to be thermally controlled. The present methodology is directly applicable even in the cases of the cyclopropyl-substituted aldehydes, where rapid rearrangement of the cyclopropyl acyl radical intermediate can potentially occur. A mechanistic approach for this new reactivity of C(60) has been also provided, based mainly on intra- and intermolecular deuterium isotope effect studies.

Chemical evidence of singlet oxygen production from C60 and C70 in aqueous and other polar media

Abstract Fullerene C60- and C70-surfactant systems sensitize the photooxygenation of singlet oxygen acceptors in aqueous and other polar media.

Regioselective reaction of singlet oxygen with α,β-unsaturated esters

Abstract The reaction of singlet oxygen with α,β-unsaturated esters shows a general preference for hydrogen abstraction on the alkyl group geminal to the ester.

Fullerene C60 and C70 photosensitized oxygenation of olefins

Abstract C 60 and C 70 sensitize the photooxygenation of 2-methyl-2-butene as well as (E)-2-methyl-2-pentene-1,1,1-d 3 by the intermediacy of singlet oxygen. Addition of DABCO reduces substantially the rate of photooxygenation. The regio- and stereoselectivity of these reactions are reported.

Decatungstate-Mediated Radical Reactions of C60 with Substituted Toluenes and Anisoles: A New Photochemical Functionalization Strategy for Fullerenes

A convenient, highly efficient, decatungstate-mediated chemical methodology to functionalize fullerenes is demonstrated. A variety of radicals have been generated by the photochemical interaction of tetrabutylammonium decatungstate [(n-Bu4N)4W10O32] and para-substituted toluenes, anisoles, and thioanisole and effectively trapped by the [60]fullerene affording the corresponding 1,2-dihydro[60]fullerene monoadducts in moderate to good yields.

Selective Reduction of Diaryl or Aryl Alkyl Alcohols in the Presence of Primary Hydroxyl or Ester Groups by Etherated Boron Trifluoride-Triethylsilane System

Abstract Diaryl or aryl alkyl carbinols bearing a second reducible functional group (such as hydroxyl or ester) are selectively deoxygenated in high yields by the action of etherated boron trifluoride and triethyl silane reducing system.

Unraveling the Mechanism of the Singlet Oxygen Ene Reaction: Recent Computational and Experimental Approaches

The mechanism of the singlet oxygen ene reaction has been a subject of renewed interest within the last few years. The main question being whether this reaction proceeds through a concerted mechanism or if it involves discrete intermediates. In general, the majority of experimental and computational studies support a traditional stepwise mechanism involving a perepoxide-like intermediate. In this minireview we highlight the most prominent and recent theoretical, as well as experimental results relating to the challenging mechanism of the singlet oxygen ene oxyfunctionalization.

Regioselective reaction of singlet oxygen with cis-alkenes

Abstract The reaction of singlet oxygen with cis olefins is regioselective and shows a general preference for hydrogen abstraction on the larger alkyl group of the double bond.

Photosensitized Oxidations of Substituted Pyrroles: Unanticipated Radical-Derived Oxygenated Products

Photooxidation of pyrrole adducts 7-10 has been investigated in order to establish a general reaction pattern and mechanism for the formation of the resulting oxygenated products. The reactions were performed in several solvents utilizing both type I and type II sensitizers. In most cases, photooxidations gave complex mixture of products. Among these products, 5,5- or 6,5-bicyclic lactams (11, 15, and 19), maleimide 12 unsaturated gamma-lactams (16 and 20), 5-hydroxylactams (13, 17, and 21), and 5-methoxylactams (14, 18, and 22) were isolated and characterized. Photooxidation of 2,5-dimethyl-substituted pyrrole 10 in aprotic solvents unexpectedly afforded aldehyde 23 as the major product. Moreover, photooxidation of pyrrole adduct 10 in protic solvents exclusively gave the unprecedented solvent-trapped products 24-27. The formation of products 11-22 was rationalized by the intermediacy of a common endoperoxide intermediate, which could be formed by both type I and type II mechanisms. Compounds 23-27 were most probably formed via an electron-transfer mechanism.

Radical Reactivity of Aza[60]fullerene: Preparation of Monoadducts and Limitations

Six aza[60]fullerene monoadducts were synthesized by the thermal reaction between the azafullerene radical C(59)N* and 9-alkyl-substituted fluorenes, 9,10-dihydroanthracene, or xanthene. Unlike fluorenes, dihydroanthracene, and xanthene, the structurally related substituted diphenylmethanes, ethylbenzene, cumene, 1,2-diphenylethane, 5,6,11,12-tetrahydrodibenzo[a,e]cyclooctene, 10,11-dihydro-5H-dibenzo[a,d]cycloheptene, 9-methylanthracene, and 9-benzylanthracene do not lead to the isolation of azafullerene monoadducts. Moreover, 1,2-dichlorobenzene, the most commonly utilized solvent for azafullerene reactions, reacts slowly with the azafullerenyl radical C(59)N* affording the corresponding aza[60]fullerene monoadduct.