Masked β-, γ- and δ-lithium ester enolates: useful reagents in organic synthesis

The reaction of ω-chloro orthoesters 1 with lithium and a catalytic amount of 4,4′-di-tert-butylbiphenyl (DTBB, 5% molar) in the presence of different electrophiles [ButCHO, PhCHO, (CH2)5CO, Et2CO, PhCOMe, PhCHNPh, Me3SiCl] in THF at −78°C leads, after hydrolysis and acid-catalysed methanolysis, to functionalised methyl esters 2. In the case of chlorotrimethylsilane, hydroxyethyl esters 2′ are isolated. The reaction is also applied to bicyclic orthoesters 3: whereas β-chloro derivatives and carbonyl compounds gives directly γ-lactones 4 after hydrolysis, the corresponding γ-chloro derivative affords the expected methyl esters after methanolysis.