Naslov
A REVISED MECHANISM FOR THE SULFUR DIOXIDE CATALYZED ALKENE ISOMERIZATION

Autori
Dean Marković, Pierre Vogel

Vrsta, podvrsta i kategorija rada
Sažeci sa skupova, sažetak, znanstveni

Izvornik
Book of abstracts 13th European Symposium of Organic Chemistry (ESOC 13) / - , 2003

Skup
13th European Symposium of Organic Chemistry (ESOC 13)

Mjesto i datum
Cavtat, Hrvatska; Dubrovnik, Hrvatska, 10.09.2003. - 15.09.2003

Vrsta sudjelovanja
Predavanje

Vrsta recenzije
Međunarodna recenzija

Ključne riječi
SO2, radicals, Isomerization, allyl, deuterium labelling, mechanistic studies

Sažetak
A NEW SEQUENTIAL METOD FOR THE HYDROLYSIS OF ALLYL ETHERS INDUCED BY A "GREEN" CATALYST: A NEW STIRATEGY FOR ALCOHOL DEPROTECTION. Dean Marković and Pierre Vogel* Swiss Federal Institute of Technology, Institute of Molecular and Biological Chemistry Laboratory of Glycochemistry and Asymmetric Synthesis, BCH CH-1O15 Lausanne- Dorigny Dean.Markovic@epfl.ch ; Pierre.Vogel@epfl.ch Polysulfones ( copolymers of alkene and S02) are capable to isomerise alkenes. The proces simplies the formation of an initial allyl radical, formed by a chain-process involving the hydrogen transfer between the alkene and the intermediate allyl radical. The formation of the latter intermediate is two steep process in which a RSO2 radical abstracts first an electron from the alkene with formation of an radical cation. In the second steep the latter loses a proton with formation of an allyl radical. Accordingly, the rate of the polysulfone catalysed alkene isomerisation depends strongly uopon its ionisation potential. This fact has been used to invent a new strategy for alcohol, aldehyde, ketone and hemiacetal protections. While allyl ethers are not isomerised with polysulfone, methallyl ethers are isomerised into the corresponding enol ethers (and then hydrolysed) on heating with polysulfone catalyst. Prenyl ethers and methylprenyl ethers are isomerised much faster. A polyol protected as allyl, metallyl and methylprenyl ethers will be deprotected under neutral conditions by the polysulfone with the following reaction sequence: methylprenyl> prenyl>> methallyl, allyl (not reactive). Under our conditions (neat + polysulfone catalysts ; or octane ; or CH2Cl2 solution + polysulfone catalyst) sillyl and benzyl as well as esters were not hydrolyzed. The metod has been applied to the protection of aldehydes and ketones as isoprenylketals. The later are deprotected by our polysulfone under neutral conditions! A REVISED MECHANISM FOR THE SULFUR DIOXIDE CATALISED ALKENE ISOMERISATION Dean Marković and Pierre Vogel Swiss Federal Institute qf Technology, Institute oj Molecular and Biological Chemistry Laboratory of Glycochemistry and Asymmetric Synthesis, BCH CH-1015 Lausanne- Dorigny Dean.Markovic@epfl.ch ; Pierre. Vogel@epjl.ch When dissolved in SO2 methylidenecyclopentane undergo two reactions: 1. Formati on of poly(methylidenecyclopentane su I fone). 2. Isomerisation into l-methylcyclopent-1-ene. EPR studies of the copolymerization reaction confirms the presence of sulfonyl and carbon centered radicals. If Bu3SnH or TEMPO are added to the reaction mixture neither polysulfone nor isomerized olefin are seen. Kinetics of the isomerization and polymerization reactions of the methylidenecyclopentane and sulfur dioxide confirmed the role of polysulfone in the isomerization reaction. Mechanistical studies shows that sulfonyl radicals trapped in the polysulfone can catalyze the isomerization. It occurs via the intermediary of methylidenecyclopent-2-yl radical (radical chain process (eq. 3.)), as demonstrated by deuterium Iabelling experiments. This is not the mechanism proposed earlier.1 (a) D. Masilamani, M. M. Rogic, J. Am. Chem. Soc. 1978, 100, 4634 ; (b) D. Masilarnani M. E. Reuman, M. M. Rogic, J. Org. Chem. 1980, 45, 4602 ; (c) M. Rogic, D. Masilamani, J. Am. Chem. Soc. 1977, 99, 5219

Izvorni jezik
Engleski

Znanstvena područja
Kemija

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