Addition of Halocarboxylic Acids Esters and Halohydrocarbons to Pentafluorobenzaldehyde Promoted by Iron Pentacarbonyl

Abstract

Iron pentacarbonyl is an efficient promoter of addition to the carbonyl group of pentafluorobenzene of alkyl a-halocarboxylates and alkyl halides. The electron-acceptor character of the pentafluorophenyl group essentially affects the course of reaction and the nature of the arising products.

Pentafluorophenyl carbonyl compounds in the Reformatsky-type reactions promoted with Fe(CO)5-based metal complex systems

“…The use of pentafluorobenzaldehyde 1 in the Reformatsky-type reactions allowed us to open the route to a wide circle of functionally substituted secondary alcohols containing a pentafluorophenyl group [24]. A sharp increase in the yields of the adducts was observed when going from perfluorobutyl iodide to allyl iodide; this is associated with the fact that electrophilic pentafluorobenzaldehyde 1 much more readily reacts with a nucleophilic reagent than with an electrophilic one.…”

“…The transition state of the reactions can be represented in the form of organoiron complex (B), including either 1 (or 4 or 5) and anion resulted from the electron transfer in the system Fe(CO) 5 -RX (X = Hal) [24]. The strong electron-accepting effect of the pentafluorophenyl group facilitates the nucleophilic attack of the anion at the electrophilic centre of the carbonyl compound.…”

“…The reaction products were isolated either by crystallization (solids) or preparative GLC (liquids) using the phase that was used in GLC analysis. The yields were determined by GLC using an internal standard [24]. …”

“…The above reactions are characterized by high yields, high selectivity, and they can be carried out under simple conditions such as either refluxing in benzene for several hours or standing at room temperature, there is no need to use anhydrous solvents and inert atmosphere. We studied these reactions by the example of various types of carbonyl compounds and concluded that the presence of Fe(CO) 5 is most effective in the case of pentafluorobenzaldehyde 1, this made it possible to perform additions of various organohalogen compounds to 1 [24]. For instance, a striking example of the Fe(CO) 5 -promoted reaction is addition of allyl iodide to aldehyde 1 that occurs under mild conditions to give secondary alcohol CH 2 CHCH 2 -CH(OH)-C 6 F 5 (2) in almost quantitative yield [24].…”

“…We studied these reactions by the example of various types of carbonyl compounds and concluded that the presence of Fe(CO) 5 is most effective in the case of pentafluorobenzaldehyde 1, this made it possible to perform additions of various organohalogen compounds to 1 [24]. For instance, a striking example of the Fe(CO) 5 -promoted reaction is addition of allyl iodide to aldehyde 1 that occurs under mild conditions to give secondary alcohol CH 2 CHCH 2 -CH(OH)-C 6 F 5 (2) in almost quantitative yield [24]. We have also showed that aldehyde 1 undergoes diastereoselective reductive coupling in the presence of [Fe(CO) 5 + HMPA] system to form the corresponding decafluorodihydrobenzoine C 6 F 5 -CH(OH)-CH(OH)-C 6 F 5 (3) [25].…”