Occidentalols synthesis

Obidoxime chloride as insecticide, 2, 516 Obtusilactone H NMR, 4, 578 Occidentalol synthesis, 1, 472 Octaaza[14]annulenes bis w-excessive, 7, 717 Octacoral... 

The trans-cis isomerization process observed in the eudesmane/germacrane ring system has been utilized for the synthesis of the c/s-fused sesquiterpene occidentalol, 48a, and its 7-epi isomer, 48b (Scheme ll)22. Photolysis of the traws-fused diene 45 at —78°C afforded triene 46, which upon warming underwent disrotatory electrocyclization to give 47a and 47b as a 1 2 mixture of diastereomers. Apparently, the carboalkoxy group imparts... 

This method was used for reduclion of the ketal dienol (3) to the ketal diene (4) yield 70%. The ketal diene (4) was used as an intermediate in a total synthesis of the sesquiterpene ( )-occidentalol (5). ... 

One of the most general reaction sequences for the transformation of ketones into alkenes is reduction of the ketone to the corresponding alcohol followed by dehydration. While this method has been widely used, it often suffers from a lack of both stereo- and regio-chemical control in the formation of the double bond. Since the reduction of ketones and the subsequent dehydration of the resultant alcohols are covered in depth in other sections (this volume, Chapter 1.1 and Volume 6, Chapter 5.1), we present here only a few representative examples and divert the reader to these other sections for a detailed analysis of this area. In the total synthesis of (+)-occidentalol (Scheme 4), 1,2-reduction of the enone moiety gave... 

A second synthesis of (— )-occidentalol (304), the enantiomer of the naturally-occurring compound, has been reported by Ando et The three-step... 

A useful synthesis (ref.ll)of patchouli alcohol, an important fragrant constituent of patchouli oil, from (+)-camphor, that onetime important natural product which was employed as a plasticiser for nitrocellulose (itself a semi-synthetic polymer), was complicated by structural revision of the sesquiterpene alcohol. Dihydrocarvone (14) obtained by saturation of the ring double bond in carvone, a major constituent of oil of spearmint has been employed for two very different sesquiterpenes, the ketone campherenone (15) and the alcohol, occidentalol (16). In the first case an enol acetate was converted to a bicyclic intermediate by earlier established methodology and the route emulated a plausible biogenetic sequence giving racemic campherenone (ref.12) as shown. Any chirality in (14) is apparently lost. 

In the synthesis of occidentalol (ref. 13), a eudesmane-type compound consisting of a cis-fused decalin containing a homoannular 1,3-diene system, dihydrocarvone was converted by a typical Robinson annellation reaction to the basic reguired bicyclic structural unit. (It is of interest that a related bicyclic methyldecalenone structure, the Wieland-Miescher ketone, has been employed for the synthesis of longifolene (ref.14), copaene (ref.15) and sativene (ref.16) by three totally different strategies outside the present concept of the semi-synthetic approach). 

The basic permanganate oxidation of conjugated 1,3-dienes is different from those reported for the 1,4-dienes above. Therefore, in the oxidation of cyclopentadiene and 1,3-cyclohexadiene (13) a mixture of five products 14-18 is obtained (equation 4) . In this reaction 14 and 16 are derived from the normal cis hydroxy la tions whereas 17 and 18 were said to be formed from 15 by hydration in what the authors term an epoxidic pathway. Formation of epoxy-diols under similar permanganate oxidations has been found for occidentalol (19), levopimaric acid (20) and a 1-chloro- or 1-bromo-l,3-diene (21) as an intermediate step in the synthesis of (+)-D-c/tfrc-3-inosose and (+)-D-c/r/ro-3-inositol (equation 5). The explanation for the epoxide formation in the oxidation of 1,3-dienes (13, 19-21) is not clear but may be connected to the fact that other additions of permanganate to dienes are possible beyond those commonly observed... 

In 1,2-alkylative carbonyl transpositions where the carbonyl group moves forward into the newly added fragement, e. g. 63 - 64, the reagent behaves as an acyl anion equivalent. We have seen one example of this in the synthesis of the occidentalol intermediate 8. Phosphine oxides with OR or SR substituents on the a-carbon 65 are ideal reagents for this process as the Horner-Wittig reaction gives vinyl compounds which can be hydrolysed to 64. 

Modification of the synthetic strategy previously used " in the synthesis of ( )-occidentalol (c/. Vol. 8, p. 103) has resulted in a new synthesis of a-santonin (418) and its less stable /S-epimer (419) (Scheme 36). An extension of previous... 

Two groups " have independently reported the synthesis of (+ )-occident-alol (254) starting from the same intermediate (253) which, in turn, can be obtained from (+ )-dihydrocarvone. The tw-o routes are depicted in Scheme 26. Cooccurring w ith occidentalol in Thuja occidentalis L. is the related alcohol, occidol (255). has now reported a third synthesis of this compound starting from... 

This sequence was used by D. S. Watt and E. J. Corey in a synthesis of occidentalol Tetrehedron Lett., 1972, 4651). 

An example of the use of electrocyclizations in organic synthesis is the preparation of both ( + )- and (-)-occidentalol by a path involving first a photochemical, conrotatory ring opening of a cyclohexadiene to a cyclohex-atriene and then a thermal closing to a mixture of diastereomeric cyclohexadiene epimers (equation 11.18). ... 

One step in the synthesis of occidentalol, a natural product isolated from the eastern white cedar tree, involved the following reaction. Identify the structure of A and show how A is converted to B. 

Hortmann s biomimetic synthesis of (+)-occidentalol 65 and of 7-e/7Z-(-)-occidentalol 64 built on these observations (Scheme 19.17). Ester 60 was prepared in several steps from (-l-)-carvone. Irradiation of 60 at —78°C in ether... 

Occidentalol is a eudesmane-type sesquiterpene isolated from the wood of Eastern white cedar Thuja occldentalis Linn.), and is characterized by the presence of a c/s-fused decalin system and a homoannular 1,3-diene unit in the molecule, an intriguing combination of functional groups rarely encountered in this class of natural products. Three related syntheses of occidentalol, all of which are based on hexahydronaphthalen-2-one intermediates have been reported, and utilize the carbonyl group for introduction of the diene chromophore in ring A 1-3,5 synthesis outlined below, utilizing a c/s-fused decalone derivative (A) illustrates several of the key features of these syntheses. 

An interesting feature of the synthesis of occidentalol by Hortmann etal. is conversion of a trans to a c/5-fused bicyclic diene by a photolysis-recyclization sequence. The key steps of this synthesis are outlined below. 

In a direct approach for the synthesis of occidentalol, Corey and Watt used the Diels-Alder reaction with an a-pyrone for establishing the c/5-fused decalin system, followed by elimination of the lactone bridge in the adduct for generation of the homoannular 1,3-diene unit. 

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