2-Pyrone 4-hydroxy-6-methyl-, alkylation

Desyl ethers are key intermediates in the synthesis of biologically active furano-pyrones. MW-assisted synthesis of these compounds has been performed in an open vessel under PTC solvent-free conditions (Eq. 23) by alkylation of 7-hydroxy-4-methyl coumarin with desyl chloride [36]. 

Additional examples of this fascinating chemistry are listed in Table 1 [9, 10]. For Entries 1-3, the initially formed m-chlorobenzoate product is methanolized to the methyl ether (not shown). Entry 3 represents an attractive synthesis of pyrrolo[3,2-d]pyrimidines [11]. Water is the nucleophile in Entry 4, not m-chlorobenzoate, in a sequence that provides pyrrolo[3,2-c]coumarins [12]. Entry 5 describes the preparation of pyrrolo[3,2-c] [1] benzothi-opyran-4-ones, which is a new ring system and where water has captured the intermediate 3-methylene-2-hydroxy indoline [13]. Entry 6 features the synthesis of pyrrolo[3,2-c]pyrones [14]. Entry 7 describes a similar rearrangement of A-alkyl-A-allenylmethylanihnes with magnesium monoperoxyphthalate (MMPP) to afford 2-vinylindoles [15], This reaction presumably follows the one described earlier, although none of the presumed intermediates could be isolated. 

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