Studies towards the synthesis of secoiridoids

Synthesis of a Seco iso-Secologanin Aglycone Analogue of Interest toward Secoiridoids and Monoterpene Indole Alkaloids

We report the access to an acyclic iso-secologanin aglycone analogue relevant to secoiridoids and monoterpene indole alkaloids. Its synthesis involved the regioselective allylic alkylation of a linear dienyl carbonate with dimethyl malonate, which was catalyzed by an iridium complex, and an anti-Markovnikov Wacker-type oxidation of the terminal alkene of the branched product that was obtained. The thus-formed aldehyde was engaged in a Pictet-Spengler reaction with tryptamine toward monoterpene indole alkaloids.

An Experimental Stereoselective Photochemical [1s,3s]-Sigmatropic Silyl Shift and the Existence of Silyl/Allyl Conical Intersections

We report an experimental discovery and computational investigation of the first photochemical stereoselective [1,3]-sigmatropic silyl shift of an allylsilane. An organocatalytic enantioselective cascade annulation generates a trimethylsilyl-o-isotoluene reactant in >99:1 e.r., and this trimethylsilyl-o-isotoluene contains an allylic silane moiety that undergoes a stereoselective photochemical [1,3]-silyl shift to form a benzylsilane with 96:4 e.r. The mechanism of this unprecedented [1,3]-silyl shift has been elucidated by a series of experimental studies and CASSCF, DFT, and TD-DFT calculations on model systems and the experimental system. The highly stereoselective photoreaction is proposed to occur via a singlet silyl/allyl conical intersection. This is a new demonstration of the role of conical intersections in selective photochemistry.

Preparation of Substituted 2H-Pyrans via a Cascade Reaction from Methyl Coumalate and Activated Methylene Nucleophiles

The reaction of methyl coumalate with a wide range of methylene active compounds, such as keto-esters or keto-sulfones and cyclic or acyclic diketones, afforded more than 30 2,3,5,6-tetrasubstituted 2H-pyrans. The reaction proceeds via a cascade reaction involving a Michael addition-6π-electrocyclic ring opening-proton transfer and 6π electrocyclization, in which a variety of functional groups were tolerated.

Divergent synthetic route to new cyclopenta[c]pyran iridoids: syntheses of jatamanin A, F, G and J, gastrolactone and nepetalactone

Six natural iridoids including jatamanin A, F, G and J, gastrolactone and nepetalactone have been synthesized via the efficient transformation of a core cyclopenta[c]pyran intermediate. Key features of the syntheses include the stereoselective construction of the core cyclopenta[c]pyran skeleton of the iridoid lactones via a Pd(0)-catalyzed intramolecular allylic alkylation, and the facile transformation of the common intermediate into natural iridoids.