Zur Umlagerung von Li‐Alkoxiden aus Dichlormethyllithium und Carbonylverbindungen in α‐Chloroxirane und α‐Chloraldehyde

Abstract

Die Addition von Dichlormethyllithium an Carbonylverbiiidungcn ergibt dic U-Alkoxide 2, deren Protolyse die Alkohole 3 (Tab. 1) und dercn Trimethylsilylierung die Silylather 4 (Tab. 2) liefert. Die Bcreitschaft der Li-Alkoxide 2 zur Umlagerung in r-Chloroxirane bzw. a-Chloraldchyde (bei SO -90°C) hiingt yon sterischen und elektronischen Substituenteneinflussen ab. Die expcrimcntellcn Ergcbnisse werden mechanistisch interpretiert. On the Rearrangement of Li Alkoxides from Dichloromethyllithium and Carbonyl Compounds into a-Chlorooxiranes and a-ChloroaldehydesThe Li alkoxides 2, formed from dichloromethyllithium and carboiiyl compounds, yicld the alkohols 3 (table 1) and the silyl ethers 4 (table 2) on protolysis and trcatmcnt with trimethylchlorosilane, rcspectively. The ability of the Li alkoxides 2 to rearrange (at 80-90°C) into a-chlorooxiranes or a-chloroaldehydes is significantly influenced by steric as well as electronic substituent effects. A mechanistic interpretation of the experimental results is given.Die Addition von Dichlormethyllithium an Diarylketone (1, R1 ==RZ =Aryl) ergibt bekanntlich (nach Hydrolyse) die zugehorigen Alkohole 3 und bildet zusammen mit deren Dehydratisierung ZLI den Dichloriithylenen 5 eine einfache und ergiebige Methode zur Dichlorolefinierung dieser Ketone2.3).

Continuous flow synthesis enabling reaction discovery

“…Early studies 74 describing the addition of dichloromethyl lithium to carbonyl compounds and a subsequent homologation through a Meinwald-type epoxide-aldehyde isomerisation process inspired Luisi and co-workers to exploit flow processing to investigate this transformation. This work demonstrated how flow chemistry effectively tames the unstable lithium dihalocarbenoid species en route to generating α-chloro aldehydes bearing a quaternary center.…”

Flow Microreactor Technology for Taming Highly Reactive Chloroiodomethyllithium Carbenoid: Direct and Chemoselective Synthesis of α-Chloroaldehydes

“…Moreover, with the exception of few cases shown by Renaud, these approaches cannot be applied to a direct synthesis of α-chloro aldehydes bearing quaternary centers. A different approach, based on carbonyl homologation followed by a Meinwald-type epoxide–aldehyde isomerization, was reported in the 1970s by Kobrich (Scheme d) . Nevertheless, the process required the internal quenching of the unstable dichloromethyllithium at very low temperature (−100 °C) and, as a second step, a thermally induced isomerization.…”