Masked omega-lithio ester enolates: synthetic applications

The protocol of lithiation by means of lithium and a catalytic (5% molar) amount of DTBB (4,4'-di-tert-butylbiphenyl), applied to omega-chloro ortho ester 6 under Barbier-type conditions gives, after final acid-catalyzed methanolysis, the corresponding functionalized esters 8 or 9 (for chlorotrimethylsilane as electrophile) or, after ortho ester deprotection and acid catalyzed treatment, the delta-lactones 11. The procedure is also practical for bicyclic ortho esters 14: the beta-chloro OBO ester derivate generates the gamma- lactones 15 and the gamma-chloro OBO ester gives corresponding esters 8.