A novel palladium‐catalyzed Heck‐type reaction of thiocarbamates has been designed to construct bridged seven‐membered‐ring systems that are otherwise challenging to prepare. Taking advantage of this newly developed method, enantioselective syntheses of lyconadins A–E (1–5), lycopecurine (6), and dehydrolycopecurine (7) have been realized in a divergent fashion. Our synthetic strategy also features an intramolecular cyclization of a N‐chloroamine to forge the C6−N bond, a transannular Mannich‐type reaction of a cyclic nitrone to stitch the C4 and C13 together, and a cyclocondensation to deliver the (dihydro‐)pyridone motif.
The ion–molecule reaction is one of the most important pathways for the formation of new interstellar chemical species. Herein, infrared spectra of cationic binary clusters of acrylonitrile (AN) with methanethiol (CH3SH) and dimethyl sulfide (CH3SCH3) are measured and compared to those previous studies of AN and methanol (CH3OH) or dimethyl ether (CH3OCH3). The results suggest that the ion–molecular reactions of AN with CH3SH and CH3SCH3 only yield products with S…HN H-bonded or S∴N hemibond structures, rather than the cyclic products as observed in AN-CH3OH and AN-CH3OCH3 studied previously. The Michael addition-cyclization reaction between acrylonitrile and sulfur-containing molecules does not occur due to the weaker acidity of CH bonds in sulfur-containing molecules, which results from their weaker hyperconjugation effect compared to oxygen-containing molecules. The reduced propensity for the proton transfer from the CH bonds hinders the formation of the Michael addition-cyclization product that follows.
An ovel palladium-catalyzed Heck-type reaction of thiocarbamates has been designed to construct bridged sevenmembered-ring systems that are otherwise challenging to prepare.T aking advantage of this newly developed method, enantioselective syntheses of lyconadins A-E (1-5), lycopecurine (6), and dehydrolycopecurine (7)have been realized in ad ivergent fashion. Our synthetic strategy also features an intramolecular cyclization of aN -chloroamine to forge the C6ÀNbond, atransannular Mannich-type reaction of acyclic nitrone to stitch the C4 and C13 together,a nd ac yclocondensation to deliver the (dihydro-)pyridone motif. Figure 1. Lycopodium alkaloids 1-8.
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