A stereocontrolled synthesis of epoxide 6, which represents the Cn–Cn+7 or “eastern moiety” building block for the title compounds, has been realized in 19 steps. Our synthesis started from tetrabromoacetone 26 and afforded dibromotriene 33b in six steps. The latter was subjected to a ring‐closing metathesis, which gave the dibromovinyl‐substituted lactone 34 in high yield. A highly stereoselective conjugate addition/enolate aldolization sequence established the additional stereocenters with perfect selectivity. Epoxide 47b was reached in another eight steps, which included a C–SiMe2Ph → C–OH oxidation in the presence of an acetal group. The final structure 6 was completed by hydrostannylation/brominolysis.
Flow chemistry is widely used nowadays in synthetic chemistry and has increasingly been applied to complex natural product synthesis. However, to date flow chemistry has not found a place in the area of biomimetic synthesis. Here we show the syntheses of borrerine derived alkaloids, indicating that we can use biomimetic principles in flow to prepare complex architectures in a single step.
An enantioselective preparation of O-acetylcyanohydrins has been accomplished by a three-step telescoped continuous process. The modular components enabled an accurate control of two sequential biotransformations, safe handling of an in situ generated hazardous gas, and in-line stabilization of products. This method proved to be advantageous over the batch protocols in terms of reaction time (40 min vs 345 min) and ease of operation, opening up access to reactions which have often been neglected due to safety concerns.
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