Masked ω-Lithio Ester Enolates: Synthetic Applications

Abstract

Abstract:The protocol of lithiation by means of lithium and a catalytic (5% molar) amount of DTBB (4,4'-di-tert-butylbiphenyl), applied to ω-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 δ-lactones 11. The procedure is also practical for bicyclic ortho esters 14: the β-chloro OBO ester derivate generates the γ-lactones 15 and the γ-chloro OBO ester gives corresponding esters 8.

Efficient Transfer of Chelating Amides into Different Types of Esters and Lactones

“…5‐ tert ‐Butyl‐4,5‐dihydro‐2(3 H )‐furan (28c): 26,27 The bpa precursor 28b was transformed into the pertinent lactone 28c according to General Procedure E. Evaporation of the solvent led to lactone 28c (35.2 mg, 0.25 mmol, 75 %) as a colourless liquid. 1 H NMR (400 MHz, CDCl 3 ): δ = 0.95 [s, 9 H, C(C H 3 ) 3 ], 1.92–2.02 (m, 1 H, C H ), 2.08–2.16 (m, 1 H, C H ), 2.47–2.59 (m, 2 H, C H 2 ), 4.19 (dd, J = 8.8, 6.9 Hz, 1 H, C Ht Bu) ppm.…”

“…The resulting amide 28a (0.18 g, 0.53 mmol, 73 %) was isolated as an almost colourless gum after purification by column chromatography (silica gel; CH 2 Cl 2 Ǟ CH 2 Cl 2 /MeOH, 90:10). 1 [26,27] The bpa precursor 28b was transformed into the pertinent lactone 28c according to General Procedure E. Evaporation of the solvent led to lactone 28c (35.2 mg, 0.25 mmol, 75 %) as a colourless liquid. 1…”

Stereoselective Synthesis of Cyclopropylidene Iminolactones and Functionalized Cyclopropanecarboxamides Mediated by Triflic Acid

“…Cyclopropylidene iminolactones 2 were fully characterized by spectroscopic analysis. The examination of the crude reaction mixtures by NMR ruled out the formation of any detectable amount of an elusive lactam X , which would have resulted from an N ‐ rather than an O ‐attack (Scheme ). The anticipated Z ‐stereochemistry for the C=N double bond is based on the known preference for the Z isomer found for cyclic as well as acyclic imidate (O‐C=N) frameworks.…”

Orthoesters in heterocycle synthesis

“…A novel preparation of five-and six-membered lactones has recently been reported from 2-(3chloropropyl)-1,3-dioxolane (208). 102 These orthoesters are readily available from the nitriles via the Pinner synthesis. 30,[103][104] Lithium halogen exchange with lithium powder catalyzed by 4,4'-(di-tert-butyl)biphenyl (DTBB, 5 mol%) in the presence of an aldehyde under Barbier-type conditions at -78 o C, followed by hydrolysis with phosphate buffer, gave 209.…”