European Journal of Organic Chemistry
European Journal of Organic Chemistry
5 years ago

Synthesis of substituted 1-alkylidenephthalanes via lithium promoted 5-exo-dig cyclization

Ernst-Ulrich Würthwein, Bernhard Wünsch, Paul Bunse
Abstract: A one-pot synthesis of substituted 1-alkylidenephthalanes from 3-(2-bromophenyl)propyne derivatives has been developed. 3-(2-Bromophenyl)propynal acetals 9 and corresponding orthoesters 19 were treated successively with n butyllithium and various aldehydes and ketones at low temperature to obtain 1 alkylidenephthalanes 10 and 20 with various functional groups at the exocyclic methylene moiety. Halogen-metal exchange, nucleophilic addition to various carbonyl compounds, regioselective 5-exo-dig cyclization of the respective intermediate lithium alcoholate and hydrolysis represent the key steps in this Domino reaction. A two-step mechanism involving at first a synchronous cyclization to form a vinyl lithium intermediate and then a methanolate elimination leading to the respective 1-methoxy allenes is suggested based on DFT-calculations.

Publisher URL: http://onlinelibrary.wiley.com/resolve/doi

DOI: 10.1002/ejoc.201800205

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