The sesquiterpene α- farnesene increases rapidly in apples during cold storage and its autoxidation appears to play an important role in the production of the storage disorder superficial scald. To aid the identification of α- farnesene oxidation products formed in stored fruit, the oxidation of α- farnesene has been studied. A variety of reagents for photochemical allylic oxidation, hydroxylation and epoxidation have been screened to determine the site selectivity of the oxidation process.
The synthesis of conjugated trienes and related oxidation products of α- farnesene (1), principally from the epoxides of α- farnesene (1), is reported. Base-promoted ring opening of 6,7-epoxide (4) by KOBut/LiNPri2 affords the conjugated triene (2), whilst the 3,4-epoxide (5) affords trienol (7). In contrast, 10,11-epoxide (6) fails to undergo epoxide ring opening; it rearranges to the conjugated triene epoxide (8). Base-promoted ring opening of bisepoxide (9) afforded trienol epoxide (11) at -30°C, whilst cyclization to tetrahydrofurans (10a,b) occurred at room temperature. Photosensitized oxidation of 10,11-epoxide (6) followed by in situ treatment with acid gave the cyclic peroxide (3) and on reduction triol (12). Bisallylic alcohol (13) was prepared by alkylation of 3-methylsulfolene with geranial. Trienes (2) and (3) have been isolated previously as autoxidation products of α- farnesene (1) and are implicated as the causal agents of superficial scald of stored apples.
The nitrogen derivatives (6) and (7) of the perfumery acetals (2) and (3) have been synthesized from manool (1) by the Beckmann rearrangement of the oxime (10). The azo derivative (IS), possessing the bridged ring system of the acetals, was synthesized by an intramolecular Lewis-acidcatalysed cyclization of the tosylhydrazone (17).Oxidative degradation' of manool (1) gives the intran~olecular acetals (2) and (3). The former possesses a powerful ambra type odour and is used in the perfumery industry. The methoxy ortho ester derivatives (4) and (5) have also been prepared2 and derivative (4) is reported as having an odour 'comparable in quality and intensity' to that of (2). It was therefore of interest to synthesize the nitrogen analogues (6) and (7).Reaction of the methylene ketone (8), obtained from the permanganate oxidation1 of man001 (I), with hydroxylamine gave the isomeric oximes (9) and (10) in 5 : 2 ratio. The oxime stereochemistries were assigned on the basis of the amides produced under Beckmann rearrangement conditions. While only low yields of amides were obtained by direct thionyl chloride rearrangement of the oximes, yields were greatly increased by using the base-promoted rearrangement of the tosylate derivatives.The tosyl derivative (9a) of the higher R, oxime (9) gave a quantitative yield of amide (1 1) on treatment with dilute base at room temperature. As the Beckmann rearrangement proceeds by a stereospecific anti migration this establishes the E configuration of the oxime (9). Amide (1 I), Cl,H,,NO, showed NH (3235,1575 cm-') and amide carbonyl (1630 cm-') and an acetate singlet at 6 1.97 together with the typical exocyclic methylene absorptions. The C 12 methylene appeared as a broad multiplet (3.17) and the N H proton as a multiplet at lower field (5.74).The lower R F (0-tosy1)oxime (IOa) required more forcing conditions to effect rearrangement and gave a 27 % yield of the amide (12) which showed N H (3290 cm-') and amide carbonyl (1645 cm-') absorptions. A three-proton doublet (6 2.77, J 5 Hz) and a one proton multiplet (6.86) were assigned to the CH,NHCO moiety. Irradiation of the NH multiplet collapsed the doublet to a singlet, thus establishing the amide structure as (12) and hence the 2-stereochemistry of the parent oxime (10).
The structure of l9αH-lupeol methyl ether isolated from Chionochloa bromoides has been determined by 13C n.m.r. spectroscopy and X-ray diffraction. Crystals of the triterpene are monoclinic, space group P21, with a 8.071(1), b 14.5477(6), c 11.6061(4) �, β 104.466(5)�, V 319.6 �3 and Z 2. The structure was solved by direct methods, and was refined to R 0.054 for 1092 observed reflections. Previous reports of synthetic and naturally occurring 19αH-lupanes are briefly discussed, as is the distribution of the chemotaxonomically discriminating triterpene methyl ethers in Chionochloa.
The epoxidic function of 8β,9β-epoxy-9,11-secopodocarp-11-ene (1) was inert to lithium aluminium hydride but underwent extremely facile intramolecular opening by a suitably placed nucleophile. The structure of the cyclized products formed, some anomalous 1H n.m.r, chemical shifts and the behaviour of the analogous 8,17-epoxy-14,15,16-trinorlabd-12-ene (14) system are described.
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