Five-membered ring annulation via thermal rearrangement of β-cyclopropyl α,β-unsaturated ketones. A formal total synthesis of the sesquiterpenoid (±)-zizaene

. Can. J. Chem. 62, 829 (1984).The intramolecular alkylation of several bromo-and epoxy-2-methylcyclopentenones, 18-23 and 33, arc described. In all cases, except 33, alkylative cyclization occurs at the y' position to the conjoint ring systems 25-31. The "blocked" bromide 33 (y' geminal dimethyl substituent) cyclizes to the fused ring hydrindenones 35 and/or 34 depcnding upon conditions. Enolate anion generation from 3-ethyl-2-methyl-2-cyclopentenone (36) with various bases (KH, LDA, Et,N) is described and the anion populations determined by quenching with chlorotrimethylsilane to afford the enol ethers 39-41. The intramolecular alkylations are discussed.

Section: Cyclopentenonesmentioning

confidence: 99%

Intramolecular alkylation of cyclopentenones: a general route to conjoint ring systems

Antczak¹,

Kingston²,

Alward³

et al. 1984

“…Recent years have witnessed an explosive growth in the development of general methods for the construction of cyclopentanes and diverse strategies for the HO HO preparation of fused triquinane sesquiterpenes (3)(4)(5)(6)(7)(8) This interesting hydrocarbon isolated from the soft coral CapBatrig (16), a biogenetic approach via epiprecapnelladiene by nella imbricata (9) has been the object of considerable attention, Birch and Pattenden ( 17,8), the palladium-catalyzed and several tota1 syntheses have been Our studies carbonylative organortannane coupling sequence of Stille and were in progress.…”

Section: Introductionmentioning

confidence: 99%

Intramolecular Diels–Alder reactions of cyclopentadiene systems: Model studies for the total synthesis of the capnellenes

Hellou¹,

Bérubé²,

Newlands³

et al. 1988

(1988). Model studies for a general intramolecular Diels-Alder approach to the tricyclo[6.3.0.0'~6]undecene~keleton common to the capnellene marine sesquiterpenes are described. Suitably functionalized cyclopentadiene systems 14 and 21 were synthesized and their cycloaddition reactivity examined. Triene 1 4 cyclized to the tricyclic adducts 15 and 16. In contrast, the anticipated product 22 from intramolecular cycloaddition of triene 21 was not formed in isolatable yield. Instead the minor adduct (10% yield) possessed an exocyclic double bond and was assigned structure 30 based on its relative stability, as determined by MM2 type calculations, and nuclear magnetic resonance data. X-ray analysis established that the major adduct (40% yield) was a tetracyclic[6.3.1 .0'~6.0'.'o]dodecene system corresponding to 32, and which arose from competitive isomerization of the initial diene and cyclization via an e.ro transition state. [Traduit par la revue]

“…Recently, we reported on a new five-membered ring annulation method based on the preparation and thermal vinylcyclopropane-to-cyclopentene rearrangement of P-cyclopropyl a,P-unsaturated ketones (36). For example (see eq.…”

Section: Introductionmentioning

confidence: 99%

Seven-membered ring annulation and spiro-annulation processes via preparation and thermal rearrangement of β-(2-vinylcyclopropyl) α,β-unsaturated ketones

Piers¹,

Morton²,

Nagakura³

et al. 1983

Self Cite

Treatment of the β-iodo enones 4 and 26–28 with lithium (phenylthio)(2-vinylcyclopropyl)cuprate (21, mixture of epimers), followed by thermolysis (180 °C, 30–45 min) of the initially formed β-(2-vinylcyclopropyl) enones, provided excellent yields of the seven-membered ring annulation products 25 and 30–32, respectively. In similar fashion, the (E)-2-(iodomethylene)cycloalkanones 8 and 29 were transformed efficiently into the spiro-annulation products 34 and 35 respectively. When compound 36 was treated with bromoform – sodium hydroxide in the presence of a phase-transfer catalyst, the dibromocyclopropane 37 was produced. The latter substance served as the starting material for a sequence of reactions (hydrolysis with hydrochloric acid in methanol, 37 → 38; oxidation with pyridinium chlorochromate, 38 → 39; Wittig reaction with methylenetriphenylphosphorane, 39 → 40; reduction with zinc in acetic acid, 40 → 41) culminating in the stereoselective formation of cis-1-bromo-2,2-dimethyl-3-vinylcyclopropane (41). On the other hand, treatment of compound 37 with n-butyllithium (ether, −90 °C), followed by protonation of the presumed intermediate 43 and hydrolysis of the resultant product 44, provided the bromo alcohol 45 in 70% yield. The latter substance was converted into trans-1-bromo-2,2-dimethyl-3-vinylcyclopropane (47). When the cuprate reagents 42 and 48 (prepared from the bromocyclopropanes 41 and 47, respectively) were allowed to react with the iodo enones 4 and 26, the β-(2-vinylcyclopropyl) α,β-unsaturated ketones 49, 52, 54, and 56 were produced in high yields. The enone 49, upon thermolysis in refluxing n-hexane, underwent facile Cope rearrangement to produce the annulation product 50 quantitatively. In contrast, the homolog 54 was notably resistant to [3,3]-sigmatropic rearrangement and, upon thermolysis in o-xylene, o-dichlorobenzene, or collidine at elevated temperatures produced, in varying ratios, the Cope rearrangement product 55 and the isomerization product 56. Thermal rearrangement (o-dichlorobenzene, 220 °C, sealed tube) of trans-3-(2,2-dimethyl-3-vinylcyclopropyl)-2-cyclohexen-1-one (52) provided the annulation product 51 (59% yield). In contrast, the corresponding homolog 56, under very similar conditions, produced only a minor amount of the annulation product 55. In this case, the major product (trienone 57) was that resulting from a [1,5]-sigmatropic hydrogen migration (ratio of 55/57 ≈ 1:4).