Five-membered ring annelation via thermal rearrangement of β-cyclopropyl-αβ-unsaturated ketones: a new total synthesis of (±)-zizaene

1979 ◽  
pp. 1138-1140 ◽  
Author(s):  
Edward Piers ◽  
Jacques Banville
Keyword(s):  
Total Synthesis ◽  
Membered Ring ◽  
Thermal Rearrangement ◽  
Unsaturated Ketones

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

1982 ◽  
Vol 60 (23) ◽  
pp. 2965-2975 ◽  
Author(s):  
Edward Piers ◽  
Jacques Banville ◽  
Cheuk Kun Lau ◽  
Isao Nagakura
Keyword(s):  
Total Synthesis ◽  
Sodium Methoxide ◽  
Membered Ring ◽  
Yield Reduction ◽  
Thermal Rearrangement ◽  
Standard Methods ◽  
Unsaturated Ketones ◽  
Mild Conditions ◽  
Sodium Amalgam ◽  
High Yields

Treatment of the β-iodo enones 7–10 with lithium (phenylthio)(cyclopropyl)cuprate provided excellent yields of the corresponding β-cyclopropyl α,β-unsaturated ketones 11–14, respectively. When 3-isopropenyl-2-cyclohexen-1-one (16) was allowed to react with dimethyloxosulfonium methylide in dimethyl sulfoxide – tetrahydrofuran, 3-(1-methylcyclopropyl)-2-cyclohexen-1-one (17) was produced in 59% yield. Although thermal rearrangement (~425–450 °C) of compounds 11 and 17 produced high yields of the annulation products 19 and 22, respectively, similar reactions involving the β-cyclopropyl enones 12 and 13 were not efficient in terms of production of the corresponding bicyclic systems (23, 26, and/or 27, respectively). In these cases, predominant (24 + 25 from 12) or significant (28 + 29 from 13) amounts of monocyclic dienones were formed. The annulation product 22 served as a convenient starting material for a new formal total synthesis of the sesquiterpenoid (±)-zizaene (30). Conjugate addition of lithium divinylcuprate to 22 afforded the ketone 36 which was converted by standard methods (via 38 and 39) into the enone 40. Treatment of the latter substance with thiophenol in the presence of tetra-n-butylammonium fluoride gave 41, which was transformed via ketalization (41 → 42), hydroboration(42 → 43), tosylation (43 → 44), and oxidation (44 → 45) into the sulfone 45. When the latter compound was treated with potassium tert-butoxide in hexamethylphosphoramide, the tricyclic ketal sulfone 46 was produced in 85% yield. Reduction of 46 with sodium amalgam afforded the ketal 47, which upon hydrolysis under mild conditions gave the ketone 32. Treatment of the latter substance with sodium methoxide in methanol provided a 1:2 mixture of the epimeric ketones 31 and 32, which had been converted previously by Coates and Sowerby into (±)-zizaene (30).

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

1983 ◽  
Vol 61 (6) ◽  
pp. 1226-1238 ◽  
Author(s):  
Edward Piers ◽  
Howard E. Morton ◽  
Isao Nagakura ◽  
Richard W. Thies
Keyword(s):  
Elevated Temperatures ◽  
Phase Transfer ◽  
Major Product ◽  
Sigmatropic Rearrangement ◽  
Membered Ring ◽  
Minor Amount ◽  
Pyridinium Chlorochromate ◽  
Cope Rearrangement ◽  
Thermal Rearrangement ◽  
Unsaturated Ketones

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).

Convergent Total Synthesis of Principinol D, a Rearranged Kaurane Diterpenoid

2019 ◽  
Author(s):  
Timothy Newhouse ◽  
Aneta Turlik ◽  
Yifeng Chen ◽  
Anthony Scruse
Keyword(s):  
Total Synthesis ◽  
Natural Product ◽  
Late Stage ◽  
Membered Ring ◽  
Entry Point ◽  
Ketone Reduction ◽  
Coupling Approach

<div> <p>The total synthesis of principinol D, a rearranged kaurane diterpenoid, is reported. This grayanane natural product is constructed via a convergent fragment coupling approach, wherein the central 7-membered ring is synthesized at a late stage. The bicyclo[3.2.1]octane fragment is accessed by a Ni-catalyzed α-vinylation reaction. Strategic reductions include a diastereoselective SmI<sub>2</sub>-mediated ketone reduction with PhSH and a new protocol for selective ester reduction in the presence of ketones. The convergent strategy reported herein may be an entry point to the larger class of kaurane diterpenoids.</p> </div>

On terpenes. LVIII. Total synthesis of 1,1,4,8-tetramethylcycloundecane: Proof of the eleven-membered ring in humulene

1954 ◽  
Vol 19 (3) ◽  
pp. 570-580 ◽  
Author(s):  
F. Šorm ◽  
M. Streibl ◽  
V. Jarolím ◽  
L. Novotný ◽  
L. Dolejš ◽  
...  
Keyword(s):  
Total Synthesis ◽  
Membered Ring
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