Alkoxylation-lactonization synthesis

SCHEME 15.16. Intramolecular Pd-catalyzed alkoxylation-lactonization as the key step in the synthesis of trani -kumausyne according to Boukouvalas et al. ... 

The results described herein demonstrate that the )9-fragmentation reaction of alkoxyl radicals generated under oxidative or reductive conditions is well suited for the synthesis of medium-sized and macro ketones and lactones. The system hyper-... 

The bromo-alkoxylation route for the synthesis of crown ethers (6,189 5,178) has been adapted to allow the preparation of substituted mono- and di-thia-crown systems (Scheme 49). Once again, one of these sequences uses the cyclization that is effected by a sulphonyl chloride and a base, as does a recently reported preparation of oxo-crown ethers e.g. Scheme 50 for the mono-oxo-series. Studies here imply activation of the carboxy- rather than of the alkoxy-terminus by the sulphonyl chloride. The ester functions reduce the complexing ability of these macrocycles with respect to normal crown ethers. The reduction of oxo-crowns to cyclic ethers, rather than to the diols that might be expected from reduction of a lactone, by LiAlHi has been studied the crown system seems to be necessary, and the involvement of lithium complexes has been suggested. 

Miscellaneous Reactions.—a-Alkoxylated a-lithioacetates may be alkylated,may react with ketones (the products from which cyclize to f3-lactones, themselves precursors of enol ethers by CO2 elimination" ), and may be condensed with lactones, as applied in a synthesis of natural product derivatives.The trianion derived from PhCH(0H)C02H is. C-alkylated but only in mediocre yield.The anions PhSCHCO and PhSCHC02Me react efficiently with electrophiles however, the former adds 1,2 to a, 8-unsaturated ketones, whereas the latter adds 1,4- ... 

New General Synthesis of medium-ring lactones via a Regioselective -Fragmentation of Alkoxyl Radicals Generated from Catacondensed Lactols... 

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