Regioselective chemistry of methoxyxenon fluoride

Abstract

Xenon difluoride (XeF2) reacts with methanol to form an unstable reactive species CHgOXeF (1). Formaldehyde is produced quantitatively by disproportionation in the absence of unsaturated hydrocarbons or with unreactive alkenes. Hydrogen fluoride generated in situ complexes with 1 to form 2 which reacts with unsaturated hydrocarbons of intermediajte reactivity such as cisor trtms-l-phenylpropene (5c, 5t), indene (6), 2,3-dimethyl-l,3-butadiene (7), and norbornene (8) as an apparent fluorine electrophile and Markovnikov fluoromethoxy products are found.Reaction of XeF2 with methanol in the presence of boron trifluoride as catalyst forms the complex 3 which disproportionates to formaldehyde. Intermediate 3 reacts with unsaturated hydrocarbons of intermediate reactivity (5c, 5t, 6, 7, and 8) as a positive oxygen electrophile to give anti-Markovnikov fluoromethoxy products. However, very reactive (electron rich) alkenes such as dihydropyran ( 9) react rapidly with XeF2 to give a carbocation species before the intermediate 1 (or its complex 2 or 3) can be formed.Recently1® we reported on the methanolysis of xenon

Fluorolactonization of norbornenecarboxylic acids and their methyl esters with F-TEDA-BF4 and XeF2

“…The reaction in methanol [15] or in alcohols with electron-withdrawing substituents, in the presence of boron trifluoride etherate leads, aside from fluorination, to alkoxyfluorination and alcohol addition products [16]. When norbornene was fluorinated by XeF 2 in acetonitrile with photochemical initiation, unrearranged 2,3-difluorides were found and the products of addition of fluorine and acetonitrile at positions 2 and 3 of the norbornane structure [17].…”

Functionalization of Organic Molecules by Xenon Fluorides

“…In the presence of an unreactive alkene, disproportionation of methoxyxenon fluoride as reacting species was the main process, resulting in the formation of formaldehyde. Various phenyl-substituted olefins reacted in the presence of hydrogen fluoride; the formation of β-fluoro carbenium ions was suggested and the entering methoxy group followed a Markovnikov type of regioselectivity, giving methoxy fluorides which were accompanied by difluorides 82,83 . Markedly different behavior was observed when the reactions were carried out in the presence of boron trifluoride, where oxygen was the electrophilic center, with the final fluoride anion entering into the benzylic position 82,83 .…”

“…Various phenyl-substituted olefins reacted in the presence of hydrogen fluoride; the formation of β-fluoro carbenium ions was suggested and the entering methoxy group followed a Markovnikov type of regioselectivity, giving methoxy fluorides which were accompanied by difluorides 82,83 . Markedly different behavior was observed when the reactions were carried out in the presence of boron trifluoride, where oxygen was the electrophilic center, with the final fluoride anion entering into the benzylic position 82,83 . The very reactive dihydropyrane, however, reacts with xenon difluoride in methanol (also in the presence of boron difluoride) to give only the Markovnikov products, and formation of methoxyxenon fluoride is not a competitive process 83 Norbornene reacts with methoxyxenon fluoride to give difluoro-, fluoro-methoxy-and nortricyclane derivatives, their distribution depending on the catalyst used 83 (Scheme 25).…”

“…Markedly different behavior was observed when the reactions were carried out in the presence of boron trifluoride, where oxygen was the electrophilic center, with the final fluoride anion entering into the benzylic position 82,83 . The very reactive dihydropyrane, however, reacts with xenon difluoride in methanol (also in the presence of boron difluoride) to give only the Markovnikov products, and formation of methoxyxenon fluoride is not a competitive process 83 Norbornene reacts with methoxyxenon fluoride to give difluoro-, fluoro-methoxy-and nortricyclane derivatives, their distribution depending on the catalyst used 83 (Scheme 25). SCHEME 25 Xenon difluoride reacts with alcohols to form unstable alkoxy xenon fluoride intermediates; the regio-and stereochemistry of reactions with indene depends on the catalyst 84 .…”

“…Shellhamer and coworkers demonstrated that methyl hypofluorite (CH 3 OF) is formed when xenon difluoride reacts with methanol, while the formation of methoxyxenon fluoride was ruled out in the first communication 82 , but detailed studies have shown that in fact methoxyxenon fluoride is the primarily formed reacting species 83 . The reactivity of methoxyxenon fluoride in the presence of olefins depends strongly on the catalyst used 83 ; however, in the presence of unreactive alkenes disproportionation was the main process, resulting in the formation of formaldehyde. Xenon difluoride also reacts with various alcohols and the formation of unstable alkoxyxenon fluoride was suggested 84 .…”