Zur Chemic der Meldrums�ure, 2. Mitt. Synthesen von Heterocyclen, 155. Mitt.

K2CO3-Catalyzed Michael Addition−Lactonization Reaction of 1,2-Allenyl Ketones with Electron-Withdrawing Group Substituted Acetates. An Efficient Synthesis of α-Pyrone Derivatives

“…α-Pyrone is a commonly observed structural unit in many naturally occurring products that show a broad range of biological activities. , Due to the existence of functional groups such as conjugated dienes and the ester group, α-pyrones are usually utilized as important intermediates in organic synthesis. , Thus, much attention has been paid to the development of new methodology for the efficient synthesis of α-pyrones. In summary, the following are typical methodologies for the synthesis of α-pyrone: (1) lactonization reaction of various functionalized α,β-unsaturated enones, which were prepared via various methods from different starting materials; (2) cyclization of 3,5-diketocarboxylic acids; (3) Pd-catalyzed coupling−lactonization of 3-halo-(2 Z )-enoic acids with 1,2-allenic tins; and (4) Pd-catalyzed carbometalation−lactonization of 3-halo-(2 Z )- enoates with alkynes . The most obvious disadvantages for some of these methodologies are either low-yielding or lacking diversity and regioselectivity.…”