The chemistry of pseudomonic acid. Part 7. Stereochemical control in the preparation of C-2-substituted monic acid esters via the Peterson olefination

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Abstract
The preparation of 2-substituted monic acid esters (1; R ≠ H) by means of olefination reactions with the ketone (3b) and anions of the appropriate reagent (6) are described. Anions derived from 2-substituted phosphonoacetates generally did not react except for (6d) which afforded good yields of ethyl 2-fluoromonate (1g) and its isomer (5c). However, anions of α-substituted-α-silylesters reacted efficiently with (3b) but stereoselectivity was highly in favour of the biologically inactive isomonate esters (5). Only 2-fluoro- and 2-methyl-monate esters possessed antimicrobial activity.