- Alkylation of alkenes by radicals generated through photoinduced single electron transfer
-
Irradiation of 1,2,4,5-benzenetetracarbonitrile (TCB) in the presence of several donors (some 2-t-butyl-1,3-dioxolanes, pivalic acid, t-butyltrimethylstannane, t-butyldimethylsilyl n-octyl ether) leads to fragmentation of the donor radical cation to give
- Fagnoni, Maurizio,Mella, Mariella,Albini, Angelo
-
-
Read Online
- Radical addition to alkenes via electron transfer photosensitization
-
A method for radical addition to alkenes is reported which is based on the photosensitized oxidation of a tetraalkylstannane by an excited acceptor (A*), fragmentation of the radical cation, and addition of the thus formed radical to an electron-withdrawing substituted alkene (acrylonitrile and dimethyl maleate). Aromatic nitriles and esters can be used as the electron acceptors, and they are chosen in such a way that their radical anion (A?-) reduces the adduct (and not the educt) radical. In this way the adduct radical is reduced and protonated to yield the end product, and the acceptor functions as a nonconsumed electron transfer sensitizer. In several cases the alkylation occurs more efficiently in the presence of a secondary donor (phenanthrene or biphenyl). However, when the acceptor is too easily reduced in the ground state (as with 1,2,4,5-benzenetetracarbonitrile), coupling of the adduct radical with A?- competes with its reduction.
- Fagnoni,Mella,Albini
-
p. 7877 - 7880
(2007/10/02)
-
- Aliphatic Radicals from Ethers via Photoinduced Electron Transfer: Selective Formation and Chemistry
-
Irradiation of aliphatic ethers in the presence of benzene-1,2,4,5-tetracarbonitrile (TCB) has been found to cause electron transfer.The radical cations of methyl tert-butyl ether and of 1,4-dioxane are deprotonated under these conditions, and in the case of methyl neopentyl ether, both C-C and C-H bond cleavage take place.The selectivity of the cleavage is rationalized on the basis of thermochemical considerations.The alkyl radicals thus formed add to the TCB radical anion (thus aromatic substitution results) or are trapped with acrylonitrile, followed by coupling with TCB anion radical (radical-alkene addition, followed by aromatic substitution).
- Fasani, Elisa,Mella, Mariella,Albini, Angelo
-
p. 449 - 452
(2007/10/02)
-
- Radicals through Photoinduced Electron Transfer. Addition to Olefin and Addition to Olefin-Aromatic Substitution Reactions
-
The radical cations of 2,2-dialkyl- and 2-alkyl-2-aryl-1,3-dioxolanes, when generated in solution by photoinduced electron transfer to 1,2,4,5-benzenetetracarbonitrile (TCB), fragment to yield alkyl radicals.These are trapped by electron-withdrawing substituted alkenes (acrylonitrile, methyl acrylate, methyl vinyl ketone, as well as dimethyl maleate and fumarate).The radicals thus formed are either reduced by the TCB radical anion or add to it.In the first process (observed only with the diesters) the end result is reductive alkylation of the olefin, while the latter process results in an addition to the olefin-aromatic substitution reaction.The selectivity of the process is explained on the basis of steric hindrance, since the radicals react when still in the cage with the aromatic radical anion.
- Mella, Mariella,Fagnoni, Maurizio,Albini, Angelo
-
p. 5614 - 5622
(2007/10/02)
-
- Photochemical Reaction of Arenecarbonitriles in the Presence of Alkylsilanes, Silyl Ethers and Silyl Amines
-
The irradiation of benzene-1,2,4,5-tetracarbonitrile, and benzene-1,2,4- as well as benzene-1,3,5-tricarbonitrile in the presence of various tetraalkylsilanes, alkoxytrialkylsilanes, hexamethyldisiloxane or heptamethyldisilazane leads to alkylation of the aromatics.The more substituted alkyl group is selectively fragmented, and the attack takes place at the position(s) of highest spin density in the nitrile radical anion.The reaction involves electron transfer to the nitrile's singlet excited state, and the radical cation appears to cleave mainly in the initial radical ion pair.
- Mella, Mariella,d'Alessandro, Nicola,Freccero, Mauro,Albini, Angelo
-
p. 515 - 519
(2007/10/02)
-
- Electron Transfer Photoinduced Cleavage of Acetals. A Mild Preparation of Alkyl Radicals
-
Electron transfer from 2-alkyl- and 2,2-dialkyldioxolanes as well as from open-chain ketals to singlet excited benzene-1,2,4,5-tetracarbonitrile (TCNB) is followed by fragmentation of the donors radical cation to yield alkyl radicals and dialkoxy carbocations.The first species are trapped by TCNB to yield alkylbenzenetricarbonitriles (substitution of a second cyano group can be obtained sequentially) and in a minor path are reduced to alkanes, while the latter ones react with nucleophiles to give ortho acid derivatives.In view of the results of radical clock experiments, it is assumed that part of the process is a concerted (radical cation cleavage-addition to the aromatic) reaction, while another part involves the free-radical cation.On the other hand, intersystem crossing from the singlet radical ion pair to the triplet manifold causes cleavage of the acetal to the corresponding carbonyl derivative.This reaction offers a mild method for the preparation of alkyl radicals via C-C bonds cleavage.
- Mella, M.,Fasani, E.,Albini, A.
-
p. 3051 - 3057
(2007/10/02)
-
- Electron-donating Behaviour of Aliphatic Carboxylic Acids in the Photoreaction with 1,2,4,5-Tetracyanobenzene
-
Irradiation of an acetonitrile solution of 1,2,4,5-tetracyanobenzene with aliphatic carboxylic acids gives 2,4,5-tricyanoalkylbenzenes efficiently; electron transfer from the carboxylic acids to the excited tetracyanobenzene is essential.
- Tsujimoto, Kazuo,Nakao, Nobuhisa,Ohashi, Mamoru
-
p. 366 - 367
(2007/10/02)
-
- NOVEL ALKYLATION OF AROMATIC NITRILES VIA PHOTO-INDUCED ELECTRON TRANSFER OF GROUP 14 METAL-CARBON ? DONORS
-
Photo-induced electron transfer reactions of tetraalkylsilanes, -germanes, and -stannanes with aromatic nitriles afforded alkylated products.The mechanism was investigated by use of a radical clock.
- Kyushin, Soichiro,Masuda, Yukihiro,Matsushita, Kazuhiro,Nakadaira, Yasuhiro,Ohashi, Mamoru
-
p. 6395 - 6398
(2007/10/02)
-