Acylation of lithium z-β-lithioacrylates: Application to a short synthesis of lepiochlorin

Acylvinyl and Vinylogous Synthons

“…In the later case, stabilization of the lithium anion by the carboxylate system accounts for achieving deprotonation instead of halogen−lithium exchange. Further reaction with aldehydes or ketones afforded butenolides 195 101 and β-bromo-butenolides 197 102 (Scheme ), a methodology used in the synthesis of some bromobutenolide antibiotics. , When anhydrides where used as electrophiles, γ-hydroxybutenolides were obtained, which as been applied, for example, to the synthesis of the antibiotic lepiochlorin ( 199 ) (Scheme ) …”

“…103,104 When anhydrides where used as electrophiles, γ-hydroxybutenolides were obtained, which as been applied, for example, to the synthesis of the antibiotic lepiochlorin (199) (Scheme 44). 105 Moreover, fused bicyclic butenolides 203 have also been prepared by bromine-lithium exchange, but starting from bromo amide 201. This compound was obtained by condensation of cyclohexanone with the bromo Vilsmeier reagent, followed by oxidation and amidation.…”

Synthesis and reactivity of lithiated γ-functionalised ketene dithioacetals. Generation of a flexible β-lithioacrylate equivalent

“…Anion (9) with Electroplziles (Table I). -A solution of lithium diisopropylamide (LDA) [prepared from butyl-lithium (0.69 ml, 1.1 mmol; 1 .…”

“…The mixture was extracted with dichloromethane (2 x 25 ml) and the combined extracts were dried (Na,SO,), concentrated, and the residue was purified by flash chromatography to give oxidative dimer (20) as a pale yellow oil (105 mg, 58% as a 4:3 mixture of diastereoisomers), v,,,,(thin film) 3 430brand 1 580cm-'. The two diastereoisomers could not be separated but for clarity, the 'H n. Synthesis of Oxidative Dimer (20) from Anion (9) and Aldehyde (19).-3,3-Bis(phenylthio)prop-2-enal (19) (243 mg, 0.89 mmol) in T H F (2 ml) was added to a solution of anion (9) [from ketene dithioacetal (8) (336 mg, 0.92 mmol)] in T H F at -78 "C. After 30 min at this temperature, saturated aqueous ammonium chloride (2 ml) was added, followed by water (25 ml). The mixture was extracted with dichloromethane (2 x 25 ml) and the combined extracts were dried (Na,SO,) and evaporated.…”