A general and practical protocol for the tertiary‐amine‐catalysed synthesis of β‐alkoxyacrylates from primary, secondary, and tertiary alcohols is described. Of the currently used catalysts, DABCO proved to be the best one for this process. Three factors seem to influence the outcome of the reaction: (1) the nucleophilic strength of the catalyst, (2) the electrophilicity of the intermediate ammonium acrylate, and (3) the pKa/nucleophilicity of the alcohol/alkoxide nucleophile. Reactivity tuning enables the transformation of a range of tertiary alcohols into the corresponding β‐alkoxyacrylate derivatives. Differences in the reactivity of different types of alcohol allow the selective transformation of diols containing two different hydroxy groups into the corresponding monoprotected derivatives. This protocol will aid other synthetic organic chemists to easily prepare such vinyl ethers under atom‐economic, efficient, and bench‐friendly reaction conditions.
The chemical study of the red alga Laurencia viridis has led to the isolation of four new polyether triterpenoids: 28-hydroxysaiyacenol B (2), saiyacenol C (3), 15,16-epoxythyrsiferol A (4), and 15,16-epoxythyrsiferol B (5). The structures of 2 and 3 were established mainly by NMR data analysis and comparison with the well-known metabolite dehydrothyrsiferol (1). However, due to the existence of a nonprotonated carbon within the epoxide functionality, stereochemical assignments in 4 and 5 required an in-depth structural study that included NOESY data, J-based configuration analysis, comparison with synthetic models, and DFT calculations. The biological activities of the new metabolites and other related oxasqualenoids were evaluated for the first time against a panel of relevant biofouling marine organisms, and structure-activity conclusions were obtained.
A general and stereoselective method to synthesize 2,3,4,5,6-pentasubstituted tetrahydropyrans in three steps starting from three different aldehydes is described. Key substrates β,γ-unsaturated N-acyloxazolidin-2-ones were subjected to an "Evans Aldol-Prins" protocol to generate five σ-bonds and five stereocenters in only a one-pot process with yields up to 60% and excellent stereoselectivities.
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