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.
Yus
Miguel
M
Departamento de Química Orgánica, Facultad de Ciencias and Instituto de Síntesis Orgánica (ISO), Universidad de Alicante, Apdo. 99, 03080 Alicante, Spain. yus@ua.es
Torregrosa
Rosario
R
Pastor
Isidro M
IM
D001713:Biphenyl Compounds / Q000737:chemistry*; D002384:Catalysis; D004952:Esters; D008094:Lithium / Q000737:chemistry*; D000432:Methanol / Q000737:chemistry; D008956:Models, Chemical; D015394:Molecular Structure; D009942:Organometallic Compounds / Q000138:chemical synthesis / Q000737:chemistry*; D013237:Stereoisomerism
C524622:4,4'-di-tert-butylbiphenyl; D001713:Biphenyl Compounds; D004952:Esters; D009942:Organometallic Compounds; D008094:Lithium; D000432:Methanol