Aluminum oxide-induced gas-phase ring-opening in methyl substituted gem-difluorocyclopropanes, leading to 2-fluorobuta-1,3-dienes and vinylacetylenes

Synthesis of Monofluoroalkenes: A Leap Forward

“…In 2015, Volchkov and co-workers discovered that the ring opening of methyl-substituted gem-difluorocyclopropanes occurred in the gas phase when exposed to aluminum oxide (Scheme 9). 21 The yields ranged from modest to moderate for the two cases reported, but they still represent an improvement to pyrolysis in a static reactor where isomerization and elimination of difluorocarbene prevail instead. 22 Scheme 9 Pyrolysis of gem-difluorocyclopropanes over aluminum oxide In 2014, Usuki, Iio and co-workers reported the preparation of fluorinated asparagine and glutamine analogues where one of the key steps was the palladium-catalyzed formate reduction reaction of 2-fluoroallylic carbonates (Table 3).…”

“…The ring-opening of dimethyl-substituted gem-difluorocyclopropanes by exposure to aluminum oxide in the gas phase was developed by Volchkov and co-workers (see also Scheme 9, Section 2.1.3.2). 21 The ring-opening occurred at high temperatures to give the corresponding monofluoroalkenes in moderate yields with good Z selectivity (Scheme 79).…”

The preparation and properties of 1,1-difluorocyclopropane derivatives

“…Difluorocarbene generation through the decomposition of hexafluoropropylene oxide upon heating: Hexafluoropropylene oxide (HFPO, 41) is an effective and cheap reagent for the difluorocyclopropanation of simple alkyl-and aryl-substituted alkenes [52]. It undergoes decomposition to form difluorocarbene (Scheme 16) at temperatures above 170 °C either under autoclave conditions or by gas-phase co-pyrolysis [53]. Photolytic generation of difluorocarbene: Difluorodiazirine (44) is a convenient photochemical source of difluorocarbene (Scheme 17).…”