We report herein the asymmetric coupling of flow‐generated unstabilized diazo compounds and propargylated amine derivatives, using a new pyridinebis(imidazoline) ligand, a copper catalyst and base. The reaction proceeds rapidly, generating chiral allenes in 10–20 minutes with high enantioselectivity (89–98 % de/ee), moderate yields and a wide functional group tolerance.
As remdesivir is the first approved treatment for COVID-19 (SARS-CoV-2), its production is likely to be of vital importance in the near future. Continuous flow processing has been demonstrated as a key technology in the manufacturing of highvolume active pharmaceutical ingredients and is considered for use in this synthetic sequence. In particular, the challenging Cglycosylation of a pyrrolotriazinamine via metal−halogen exchange was identified as a transformation with significant potential benefit, as exemplified by calorimetric analysis of each reaction step. Multiple simplifications of this process were attempted in batch but in general were found to be unfruitful. The five-feed process was then transferred to a flow setup, where specific conditions were found to circumvent solid formation and permit stable processing. Detailed optimization of stoichiometries provided an improvement upon batch conditions with a total residence time of <1 min.
A continuous flow procedure for the gem-dichlorocyclopropanation of alkenes has been developed. The method is based on the generation of dichlorocarbene utilizing the classical biphasic aqueous sodium hydroxide/chloroform system. This reaction typically requires vigorous stirring for several hours in batch for completion. Tarry materials precipitate due to partial polymerization of dichlorocarbene and the process is difficult to scale. To overcome these problems and achieve very efficient mixing during the flow process a column reactor packed with PTFE beads as inert filling material has been used. PTFE beads have been found to be the optimal material to obtain fine dispersions of the aqueous phase in the organic solution. By heating the packedbed reactor at 80°C excellent conversions have been achieved after a residence time of only 4 min. The process has been applied for the synthesis of Ciprofibrate, a dichlorocyclopropane-containing drug used as treatment for several diseases associated with high lipid content in blood.
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