Synthese von zwei natürlich vorkommenden Lactonen mit 10gliedrigen Ringen: (±)‐Phoracantholid J und I

Synthesis of Two Naturally Occurring 10‐Membered Ring Lactones: (±)‐Phoracantholide J and I Two 10‐membered ring lactones 7 and 11 from the metasternal secretion of the eucalypt longicorn Phoracantha synonyma have been synthesized by the following method. Reaction of the dilithium derivative of 4‐pentynoic acid ( 3 ) with 4‐tetrahydropyranyloxy‐1‐pentylbromide ( 2 ), followed by removal of the protecting group and by esterification with diazomethane, gave methyl 9‐hydroxy‐4‐decynoate ( 4 ; s. Scheme 1 ). Partial hydrogenation of the triple bond in 4 with Lindlar palladium catalyst, followed by saponification lead to cis ‐9‐hydroxy‐4‐decenoic acid ( 6 ). The 9‐hydroxydecanoic acid ( 9 ) was synthesized by addition of methyl magnesium iodide to methyl 8‐formyloctanoate ( 8 ) followed by saponification (s. Scheme 2 ). The hydroxy acids 6 and 9 were converted into the S ‐(2‐pyridyl) thioesters and cyclized in dilute benzene solution under the influence of silver ions to yield (±)‐phoracantholide J ( 7 ) and I ( 11 ) in 74 and 71% yield, respectively.