Tricyclic enone lactone

The racemic synthesis of decipienin A was accomplished in the laboratory of G.M. Massanet. In the late stages of the total synthesis, the tricyclic enone lactone was converted to the corresponding a, 3-epoxyketone by treatment with hydrogen peroxide in the presence of NaOH. The epoxyketone was subjected to the conditions of the Wharton transposition to afford the cyclic allylic alcohol in excellent yield. Several subsequent steps completed the total synthesis. 

The elaboration of the tricyclic hydroxymethylene lactone 2 is summarized in Scheme III. Treatment of enone 9 with a 203 excess of N-bromosuccinimide (NBS) in refluxing carbon tetrachloride under the... 

The classic Hoffman elimination of amine iV-oxides has been performed under very mild conditions in the presence of alumina [83]. The spiro-lactone 1 is converted to the tricyclic enone 2 by heating with HY or HZSM-5 zeolite (e.g. equation 4.14) [84]. The product is recovered by extraction of the zeolite with methanol. 

Kozikowski and Li (268) also made use of this protocol for the construction of the hexahydronaphthalene portion of the hypocholesteremic agent compactin (256) (see Section 6.4.2.2). The oxime derived by from alcohol 253 (via y-lactone 252) was heated with aqueous sodium hypochlorite in the presence of triethylamine to give the tricyclic isoxazoline adduct 254 (Scheme 6.96). Reductive hydrolysis and dehydration afforded enone 255, which in several further steps led to compactin (256) (268). 

Treatment of the enone (69) with an excess of the diene (70) in the presence of aluminium trichloride and 4,4-thiobis-(6-t-butyl-3-methylphenol) gave the tricyclic ketone (71) (40%) as the sole Diels-Alder product. Reduction then afforded the lactone (72) whose constitution and stereochemistry were established by X-ray analysis. Finally, demethylation gave the racemic alcohol (73) which differs from the quassin skeleton only in the stereochemistry at C-9. The Diels-Alder reaction also plays a key role in two other de novo syntheses. The ring A seco-derivative (75) has been prepared from the adduct (74), and the ring A nor-compound (77), a possible intermediate for the synthesis of quassimarin (78), has been obtained from the Diels-Alder product (76). ... 

The ability of A -heterocyclic carbenes to activate a,p-unsaturated carbonyl compounds via the formation of the corresponding Breslow intermediate, which plays the role of a homoenolate nucleophile, has also been applied to a cascade process involving a formal intramolecular Michael reaction/oxidation/ lactonization, leading to the formation of complex tricyclic carbon frameworks starting from a bifunctional substrate containing an enone and an a,p-unsa-turated aldehyde side chain linked to each other via a benzene tether (Scheme 7.82). The reaction involved a complex multistep mechanism which started with the activation of the enal by the catalyst, forming the Breslow intermediate, which subsequently underwent intramolecular Michael reaction and next the generated enol-type intermediate reacted intramolecularly with the... 

The important anthraquinone-intermediate 810 has been synthesized in two steps from the lactone 807, which has also been used by Snider et al. for then-synthesis. With LiHMDS and cyclohex-2-enone (808), the tricyclic 809 was formed (see Scheme 12.4 (553)). Oxidation with cerium ammonium nitrate gave the anthraquinone 810. 

The Woodward synthetic route was initiated with a Diels-Alder reaction between 1,4-benzoquinone (14) and diene 15. The cycloadduct 16 formed in this way underwent Meerwein-Pondorff-Verley reduction to afford tricyclic lactone 17 which was converted to bromoether 18. Treatment of this substance with methoxide gave the methyl ether 19. Conversion of 19 to its halohydrin followed by chromium oxidation provided the a-bromo ketone 20 which upon treatment with zinc in glacial acetic acid afforded the bicyclic enone 21. This substance was transformed to the aldehyde-acid 23 by an osmylation-periodate cleavage sequence. The acid function in 23 was es-terified and the aldehyde moiety was condensed with 6-methoxytryptamine. The Schiff base intermediate obtained in this fashion was reduced to give an amine which provided the lactam 24 upon intramolecular acylation. Bischler-Napieralski cyclization of 24 gave the pentacyclic intermediate 25 in which... 

A final synthetic effort in the yohimbine alkaloid area concerns the studies reported by Loewenthal and his coworkers (Scheme 3.92) (143). The aim was to develop an efficient method to prepare the bicyclic enone 21, which serves as a key intermediate in the Woodward reserpine synthesis strategy (19). The route for preparation of 21 began with Friedel Crafts reaction of 2-methoxynaphthalene (523) with the oxalyl chloride equivalent 524, a process which afforded the acenaphthenoquinone 525. Oxidative-decarboxylation of 525 yielded the naphthalene-carboxylic acid 526 which was transformed by Birch reduction and esterification to the dihydro-derivative 527. Carboxyla-tion then provided geminal diester 528 which was epoxidized. Sequential lactonization and methylation afforded tricyclic lactone 529. Ester cleavage with subsequent decarboxylation gave lactone 530 which was demethylated to provide 531. While no further effort was given to the development of this... 

Intramolecular [2+2]-photocycloadditions of cycUc a,P-unsaturated enones with remote double bonds have been extensively used to synthesize a variety of interesting compounds, including natural products. An analysis of the mechanism of the additions has also been carried out. 2-Pyrones having pendant enes and dienes undergo synthetically useful photocycloaddition processes to give tricyclic lactones and lactone-bridged cyclooctadienes by [2+2]-and [4+4]-cydoadditions, respectively. The photochemical reactions... 

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