SummaryAlkoxychlorofluorocyclopropanes are easily prepared by chlorofluorocarbene addition to en-ethers in a two-phase system and converted by simple heating in an aqueous solvent mixture to 2-fluoro-2-alkenals which can be reduced to the corresponding alcohols.Silver-catalysed ring-opening of chlorofluorocyclopropanes derived from simple alkenes offers a convenient access to fluoroalkenols containing a tertiary hydroxy group [ l ] [2]. In acidic medium these tertiary alcohols (or their acetates) slowly undergo allylic migration and are converted to the thermodynamically more stable isomers having a primary oxygen function [2]. Numerous 2-fluoro-2-alken-1-01s (or acetates thereof) have been prepared in this manner [3]. This communication describes an easier and more efficient entry into this class of compounds.In a two-phase system [3] en-ethers can be converted rapidly in high yields into alkoxylated chlorofluorocyclopropanes which have previously been prepared by a very similar method but could be isolated only in exceptional cases. The high temperatures and the special conditions which were employed promote instantaneous ring opening of the cyclopropane products to yield 2-fluoro-2-alkenal acetals [4]. In fact, the alkoxychlorofluorocyclopropanes now obtained proved to be much more susceptible towards solvolysis than ordinary chlorofluorocyclopropanes (for facile solvolysis of alkoxy-dichloro-and alkoxy-dibromo-cyclopropanes, see [5]). They undergo clean ring-opening in an aqueous medium at reflux temperatures whereas their non-alkoxylated analogues are completely inert in the absence of catalytically active silver salts. The products of hydrolysis, a$-unsaturated and fluorinated aldehydes or ketones, can easily be reduced with lithium aluminium hydride to afford fluorinated ally1 alcohols with a primary or secondary hydroxyl group. Thus (see Scheme I), in over-all yields about 50%, methyl 2-methyl-lpropenyl ether was transformed through cyclopropane 1 and aldehyde 2 into 2-fluoro-3-methyl-2-buten-1-01 (3, 'fluoroprenol'), methyl 2-propenyl ether (through cyclopropane 4 and ketone 5) into 2-fluoro-1-buten-3-01 and methyl-') Part VIII of the series 'Syntheses of Organofluorine Compounds'; for the preceding paper see [ 11 114