Radikalische Cyclisierung von Dienen, VIII. Über die regioselektive Herstellung von ungesättigten Cyclopenta[b]furan‐2‐onen aus (S)‐(+)‐Carvon — Bausteine zur Synthese von enantiomerenreinen Triquinanen

Abstract

Radical‐Type Cyclization of Dienes, VIII[1]. — On the Regioselective Synthesis of Unsaturated Cyclopenta[b]furan‐2‐ones from (S)‐(+)‐Carvone — Building Blocks for the Synthesis of Enantiomerically Pure Triquinanes The diastereomeric products 2a and 2b, which were synthesized from (S)‐(+)‐carvone (1), are converted to (3aS,5S,6aS)‐(‐)‐5‐acetoxyhexahydro‐6a‐methyl‐2H‐cyclopenta[b]furan‐2‐one (4) in ca. 50% yield. 4 is regioselectively converted to (3aR,6aS)‐(‐)‐3,3a,6,6a‐tetrahydro‐6a‐methyl‐ (8a) and (3aS,6aR)‐(+)‐3,3a,4,6a‐tetrahydro‐6a‐methyl‐2H‐cyclopenta[b]‐furan‐2‐one (8b). These are used at the 10‐g scale for the synthesis of enantiomerically pure triquinanes.

Enantioselective Synthesis of (−)-Platensimycin Oxatetracyclic Core by Using an Intramolecular Diels−Alder Reaction

“…As shown in Scheme , commercially available (+)-carvone 6 was transformed to the known lactone 5 by slight modification of a literature procedure . Our initial Baeyer−Villiger oxidation of lactone 5 with m CPBA proceeded very slowly and the corresponding oxidation product was obtained in poor yield (20%).…”

Total Synthesis of (−)-Platensimycin, a Novel Antibacterial Agent

“…(+)-Carvone 9 was converted to lactone 8 by a modified literature procedure 34–36. Initial treatment of 9 with Hg(OAc) 2 in a mixture of THF and H 2 O followed by reduction with NaBH 4 can provide ketones 11 and 12 , as reported.…”

“…Our synthesis of the known lactone 8 is summarized in Scheme . (+)-Carvone 9 was converted to lactone 8 by a modified literature procedure. − Initial treatment of 9 with Hg(OAc) 2 in a mixture of THF and H 2 O followed by reduction with NaBH 4 can provide ketones 11 and 12 , as reported. However, this reaction generates a stoichiometric amount of mercury as a byproduct which is not convenient for large-scale synthesis.…”

“…Lactone 8 was previously oxidized to ester 14 in a single operation using m -CPBA 34–36. However, this reaction proved to be extremely sluggish and the yield was low (~20%).…”

“…Lactone 8 was previously oxidized to ester 14 in a single operation using m -CPBA. − However, this reaction proved to be extremely sluggish, and the yield was low (∼20%). Therefore, we explored a stepwise and more reliable route to this acetate, which is shown in Scheme .…”