The n-Butylthiomethylene Blocking Group 1

An efficient annelation of 2,3-dimethylcyclohexanone is described. The key step of this process involves the reaction of the enol lactone 16 with methyllithium, under carefully controlled conditions. The completely stereoselective conversion of the sesquiterpene (−)-aristolone (1) into the levorotatory decalone 22b is described. Comparison of the latter with the unambiguously synthesized racemic decalone 22a conclusively establishes the relative stereochemistry of aristolone (1).

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confidence: 99%

Annelation of 2,3-dimethylcyclohexanone. Synthetic proof for the stereochemistry of the sesquiterpene aristolone

Piers¹,

Britton²,

Waal³

1969

“…In this paper we report the stereoselective total synthesis of (-)-(I S,4S,5R77R)-1 ,7-dimethyl-4-isopropylbicyclo[3.2.1]octa-6,8-dione (23) and of (+)-(1~,4~,5~,7~) Conversion of (+)-carvomenthone (26)4 into the corresponding n-butylthiomethylene derivative 28, via the hydroxymethylene compound 27, was accomplished in 69% overall yield by standard procedures (25). Alkylation of the blocked ketone 28' with ethyl 2-iodopropionate in the presence of potassium t-butoxide in t-butyl alcohol was highly regioselective6 and stereoselective, producing in 73% yield the alkylated product 29.7 Treatment of the latter with potassium hydroxide in refluxing aqueous diethylene glycol (25) concomitantly resulted in removal of the nbutylthiomethylene blocking group and hydrolysis of the ester functionality.…”

Section: (24)mentioning

confidence: 99%

“…Alkylation of the blocked ketone 28' with ethyl 2-iodopropionate in the presence of potassium t-butoxide in t-butyl alcohol was highly regioselective6 and stereoselective, producing in 73% yield the alkylated product 29.7 Treatment of the latter with potassium hydroxide in refluxing aqueous diethylene glycol (25) concomitantly resulted in removal of the nbutylthiomethylene blocking group and hydrolysis of the ester functionality. Esterification (ethereal diazomethane) of the resulting crude keto acid 30 afforded in 85% overall yield (from 29) the keto ester 31.…”

Section: (24)mentioning

confidence: 99%

Stereoselective Total Synthesis of Copa and Ylango Sesquiterpenoids: Preparation of (−)-(1S,4S,5R,7R)-1,7-Dimethyl-4-isopropylbicyclo[3.2.1]octa-6,8-dione and(+)-(1R,4S,5S,7S)-1,7-Dimethyl-4-isopropylbicyclo[3.2.1]octa-6,8-dione

Piers¹,

Britton²,

Geraghty³

et al. 1975

Can. J. Chem. 53,2827. The efficient, stereoselective syntheses of two diastereomeric bicyclo[3.2.1]octadiones (23 and 24) are described and the potential use of these materials for the synthesis of the copa (1-5) and the ylango (7-11) sesquiterpenoids, respectively, is outlined. Conversion of (+)-carvomenthone (26) into the corresponding n-butylthiomethylene derivative 28, followed by alkylation of the latter with ethyl 2-iodopropionate, gave compound 29. Removal of the blocking group from the latter was accompanied by ester hydrolysis and afforded keto acid 30. An efficient intramolecular Claisen condensation of the corresponding ester 31 yielded ( On a transform6 I'octalone connue 39 en cCto-aldehyde 41 par des techniques standards. Le traitement de 41 par du dimethylcuprate de lithium suivi par le piCgeage de I'anion Cnolate qui en rCsulte par du chlorure d'acetyle conduit au compost 42 qui par ozonolyse oxydante fournit le cCto-acide 43. L'estkrification de ce dernier suivie par une conduisation de Claisen intramo-

“…Treatment of the latter under the usual conditions (14) with n-butanethi-01 gave in 89% yield the corresponding n-butylthiomethylene derivatives 7, which, upon reduction with a basic solution of methanolic sodium borohydride provided a quantitative yield of the crude P-hydroxythioenol ether 8. This material was not purified further, but was immediately subjected to hydrolysis with 1% hydrochloric acid in aqueous acetone.…”

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confidence: 99%

Total Synthesis of ( ± )-α-Cubebene and ( ± )-β-Cubebene

Piers¹,

Britton²,

Waal³

1971

An efficient total synthesis of the racemic forms of the novel tricyclic sesquiterpenes a-cubebene (1) and 8-cubebene (2) is described. The key step of this synthesis involved the cupric sulfate catalyzed intramolecular cyclization of the olefinic diazoketone 3, which produced, in high yield, (+)-8-cubebene norketone (24) and (f )-l,6-epi-p-cubebene norketone (25), in a ratio of approximately 3:5, respectively.