Bicyclo octene synthesis

Scheme 2.201. Synthesis of c/s-bicyclo[3.3.0]octenes via domino carbolithiation/ electrocyclization/electrophile trapping.

Mono- and bi-cyclic cyclopentanes, known precursors of variety of sesquiterpenes, have been prepared by the acid-catalysed rearrangement of 1-methylcyclo-butylmethanols. An acid-catalysed rearrangement (see Scheme 77) has been found to afford a practical method for converting a bicyclo[4.2.0]octene system (221) into a bicyclo[3.2.1]octene framework (222) in a recent synthesis of verrucarol. ... 

The bicyclo[3.3.0]octene skeleton is of interest due to its potential use as an intermediate in the synthesis of cyclopentanoid natural and nonnatural compounds. The bicyclo[3.3.0]octene skeleton can be prepared by asymmetric elimination of the corresponding alcohols on treatment with a variety of chiral amines80, S1. Bicyclic trifluoromethanesulfonales 1 on treatment with (5)-Ar,Ar-dimethyl-l-phenylethylaminc give the corresponding bicyclo[3.3.0]octenes 2 with 15,5/ -configuration with up to 89% enantiomeric excess in high yield. 

Other examples of the synthesis of cyclobutanes with abstraction of an allylic hydrogen are the photochemical formation of tricyclo[4.1.0.03,7]heptan-5-ones (e.g., 5) from norborn-5-en-2-ones33 and of bicyclo[4.2.0]octenes (e.g., 7) from doubly unsaturated ketones.34... 

Diels-Alder reactionsBoth 1,4-dicyanonaphthalene (DCN) and 2,6,9,10-te-tracyanoanthracene (TCA) have been used as sensitizers to effect photochemical [4 + 2]cycloadditions of electron-rich dienes and electron-rich dienophiles, which do not normally undergo thermal cycloadditions. These cycloadditions are known as triplex Diels-Alder reactions because they are postulated to involve as an intermediate a three-membered complex of sensitizer, dienophile, and diene. This reaction is useful for synthesis of bicyclo[2.2.2]octenes from some silyl enol ethers, alkenes, or arylalkynes. 

M. Green, J. A. K. Howard, J. L. Spencer, and F. G. A. Stone, Synthesis of Ethylene, Cyclo-octa- 1,5-diene, Bicyclo [2.2.1]heptene, and trans-Cyclo-octene Complexes of Palladium ) and Platinum(O) Crystal and Molecular Structure of Tris(bicyclo2.2.1]hepte-ne)platinum, J. Chem. Soc., Dalton Trans. 1977, 271-277. 

Cationic cycloadditions. Ionization of p-benzoquinone monoacetals is induced by MejSiOTf in highly polar media (LiClO /EtOAc) and the carbocations are captured in situ by alkenes to give bicyclo[3.2.1]octene derivatives. A synthesis of 2-(l -phenylethoxy)-8-oxabicyclo[3.2.1]oct-6-en-3-one in good enantiomeric purity from furan and a mixed acetal of 2-(triethylsiloxy)acrolein (prepared from pyruvaldehyde dimethylacetal in three steps) is promoted by MejSiOTf. 

Corey-Winter olefin synthesis (1, 1233-1234). Chong and Wiseman1 were able to demonstrate the transient existence of bicyclo[3.2.1]octene-l (2, a bridgehead alkene which violates Bredt s rule) by application of the Corey-Winter olefin synthesis. Thus treatment of the thionocarbonate (1) with triethyl phosphite at reflux (165°) for 24 hr. in the presence of 1,3-diphenylisobenzofurane (1, 342-343 2, 178-179) leads to the formation of two Diels-Alder adducts (3) and (4) derived from (2). 

Oxidative decarboxylation. Having occasion to prepare a quantity of 1-carbo-ethoxy-A -bicyclo[2.2.2]-octene (8), Grob and co-workers prepared the anhydride (6) by the neat synthesis formulated and investigated the oxidative decarboxylation with lead dioxide according to Doering (see Lead dioxide). Even with the active lead dioxide of Kuhn and Hammer, the reaction proceeded poorly and the yield of (8) was only 30-37%. The Swiss workers then found that the yield can be more... 

Bicyclo[2.2.2]octen-2-ones 25 afford tricyclo[3.3.0.0 ]octan-3-ones 26 in very good to excellent yields. Quantum yields for these conversions are in the range 0.5-1.0. The products have been used as building blocks in the synthesis of polycyclopentanoid terpenes and prostacyclin ana-logues. 2" - "... 

The range of cyclopropenes made by this route is not large and they are mostly simple alkylated cyclopropenes, but they do include a few not readily available in other ways most notably the bicyclo[4.1.0]heptenes 1 and the equivalent bicyclo[5.1.0]octenes. ° " The synthesis of the unstable 7,7-dimethylbicyclo[4.1.0]heptene (1) serves to illustrate an unusual side reaction sometimes encountered in the photolysis of 3/7-pyrazoles, namely formation of the valence tautomer The reaction is only observed at low temperatures and, as shown, the balance... 

Grieco and coworkers have utilized intramolecular aldolization of keto aldehydes to form seven-mem-bered rings. In a synthesis of ( )-helenalin, keto aldehyde (54) was cyclized to aldol (55 equation 1In a later modification of the basic approach, keto aldehyde (56) was cyclized to cycloheptenone (57 equation 113).The success of these cyclizations is related to the fact that the normally preferred five-membered ring closure would yield a strained rnzns-fused bicyclo[3.3.0]octene system. 

Synthesis and properties of cationic -conjugated systems stabilized by bicyclo[2.2.2]octene units including annulated silatropilium ion, thiophene, 1,2-dithiine, 1,4-dithiine, and oligothiophenes 05SL187. 

Similarly, the bicyclo[2.2.2]octene double bond in 28 was readily opened in a domino ROM/double RCM process, leading to tricyclic bisenone 29 with catalyst 2 under ethylene atmosphere in good overall yield from dialdehyde 27 (Scheme 2.11) [7]. Compound 29 was successfully utihzed as the key intermediate in a total synthesis of the bioactive diterpenoid (-l-)-cyanthiwigin U. 

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