The Total Synthesis of (±) β‐Acorenol. Preliminary communication

Abstract

Preliminary Communication2)Zusammmfassung. Die erste Totalsynthesc des Spiro-scsquiterpenes P-Acorenol, ausgehend vom bekanntcn Cyclohex-1-enylessigsaureathylester, wird beschrieben. Die Schliisselstufe 2 + 3 + 4 verlauft iiber eine thermische intramolekulare En-Reaktion ,&Acorenol, a spirocyclic sesquiterpene, isolated from the wood of Juni;6eyus rigida has been shown by chemical and spectroscopic evidence [l] to have structure SS). This communication describes the first total synthesis of racemic ,L?-acorenol 8 and 8-acoradiene 9 [l], the key step of which utilizes recent observations on the stereocontrolled synthesis of five-membered ring systems [4] 4 ) .The known ethyl cyclohex-1-ene-1-acetate 1 [5] was alkylated [6] with l-bromo-3-butene to give the oily diene 25) 6, (b.p. 91-92"/0.3 Torr; IR. : 1730 cm-I). The latter cyclized in toluene (19% solution in a sealed ampoule) at 280" with 3 days') to a 1:l mixture (65% yield) of the esters 35)6) and 45)6), which were separated by l) 2, 4, 5, 6 , ' ) Presented in part at the International Symposium: tNeue Methoden der Organischen Synthese)), Basle, Switzerland, May 11, 1973. The content of this communication will appear as part of a full paper in this journal. For isolation and structure of the closely related alaskenes see [2]. For previous approaches to acorane-type compounds see [3] [8]. The IR.-and NMR.-spectra were in agreement with the assigned structurc. Satisfactory elemental analytical data were obtained for this substance. 1-(5-methyl-4-hexenyl)-cyclohexene is reported not to cyclize at temperatures up to 500" [7].

Indor and 1H‐NMR. Studies of the Ansa Conformation of Hexahydrorifamycin S

“…a) are assigned to the methyl groups C (1 3), C (36), C (14) and C (37), respectively. The chemical shifts agree with those reported by Prelog & Oppolzer [7] and show no appreciablle difference from the corresponding values in 2 [4] [8] [9]. All the five (CH)-CH, methyl groups appear as distinct doublets at 6 = 0.22, 0.56, 0.69, 0.95 and 1.32 In particular, the highest field doublet, 6=0.22, is likely attributable to the methyl group at C(34) [4] [9] [lo].…”

ChemInform Abstract: A NEW STEREOSELECTIVE APPROACH TO SUBSTITUTED PYRROLIDINES BY INTRAMOLECULAR ENE‐REACTIONS

“…methyl group and the olefinic bond. be of importance for the synthesis of certain natural products, as exemplified by the following communication [17].…”

Intramolekulare En-Reaktionen in der organischen Synthese

“…oberhalb 250°C in das thermodynamisch stabilere trans-Isomer(27) iibergingen. Diese Befunde illustrieren die generelle Moglichkeit, jeweils unter kinetischer oder thermodynamischer Kontrolle cis-oder trans-substituierte funfgliedrige Ringe aufzubauen.…”