Reactions of the carbanion from an orsellinate derivative with electrophiles

Abstract

Esters of orseilinic acid dimethyl ether (11) are attacked by alkyl-lithium reagents to give ketones and in some cases smaller amounts of alkenes as a result of a second nucleophilic attack. However at –78 °C attack on (11) by its own anion (10) is sufficiently slow that the anion can be generated almost quantitatively by lithium di-isopropylamide. Reactions of the anion (10) with various simple electrophiles (D₂O, CO₂, Mel, Me₃SiCl, and Me₃SnCl) give the expected products of nucleophilic addition. With aldehydes (PhCHO and MeCHO) the initially formed alcohol lactonizes to give a dihydroisocoumarin. The anion was acylated with acetyl chloride to give the ketone (18). The reactions of the trimethylsilyl derivative (14) are in most cases very similar to the parent compound (11) but the trimethylstannyl derivative (15) regenerates the anion (10) on treatment with MeLi or BuⁿLi. Finally, reaction of the anion (10) with α-pyrone (42) unexpectedly gave the naphthopyrone (43).