8-Oxabicyclo octenes

The tosylates (104) could not be isolated but cyclized spontaneously to (105). Two approaches have been described to the oxabicyclo-octene moiety (106) that is present in certain antibiotics and nucleophilic addition of the hydroxyl function to the C=C bond in systems such as (107) has been ascribed to the relief of strain in the ground state.An intramolecular Michael addition converts (108) into (109). ... 

Oxabicyclo [3.2.1]octenes give a poor yield of the ring-opened product in low ee if reacted at room temperature with BU2AIH in the presence of the Ni(COD)2/BINAP catalyst in either toluene or THF solution (Scheme 2-21). However, if the reaction is carried out at 60°C, high yields and enantioselectivities are obtained [78]. Various substitution patterns and protective groups are tolerated (entries 11-15). 

The [5 + 2]-cycloadditions of air-stable 7]3-pyranyl and 7]3-pyridinyl molybdenum 7T-complexes (4758 and 48,59 respectively) with alkenes reported by Liebeskind and co-workers provide a novel method for the construction of oxabicyclo[3.2.1]octenes and highly functionalized tropanes (Scheme 20). This process involves the formation of a TpMo(CO)2 complex which in the presence of EtAlCl2 reacts with an alkene in a stereoselective [5 + 21-cycloaddition to give metal-complexed cycloadducts 50 and 51 (Tp = hydridotrispyrazolylborato). Metal decomplexation via protiodemetalation or oxidation affords the products in good to excellent yields (Scheme 21). 

Compared to oxabenzonorbomenes, oxabicyclo[2.2.1]heptenes or oxabicyclo[3.2.1] octenes are less reactive substrates, and the Pd-catalyzed alkylative ring-opening process with organozinc reagents generally required heating in 1,2-dichloroethane at reflux. The addition of Zn(OTf)2 dramatically improved the rate of the reaction which could be carried out in CH2C12 at room temperature, as illustrated for the conversion of 83 to the... 

Pyranones bearing pendant heteroatoms or 7i-nucleophiles undergo photochemical conversion to form diquinane, hydrindene, benzohydrindene, oxabicyclo[3.3.0]octene, and oxabicyclo[4.3.0]nonene skeletons (Scheme 41) <1998JOC2806>. 

A direct ring opening of the oxabicyclo[3.2.1]octenes shown below with DIBAL-H provided an entry to the chiral C-19-C-26 and C-27-C-32 fragments of scytophycin C <02OL245>. 

Alkyne hexacarbonyldicobalt complexes. The complexes of alkynes with Co2(CO)84 react with 2,5-dihydrofuranes to give 3-oxabicyclo[3.3.0]-7-octene-6-ones in high yield (equation I) when the reaction is conducted under a CO atmosphere. 

Treatment of the azabicyclo[2.2.1]heptene 580 with MCPBA for 3-5 s generated the oxabicyclo[3.2.1]octene 582 via a rapid Meisenheimer rearrangement of the A -oxide 581. Compound 582 was converted into the thermodynamically more stable isomeric bicyclic isoxazolidine 583 by simple heating (Scheme 142) <2000CC2451>. 

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. 

The furan nucleus undergoes cycloadditions with oxyallyl cations to produce compounds with the oxabicyclo[3.2.1]octene skeleton. Various research groups have found new ways of generating the oxyallyl cation and have also defined the types of substituted furans which undergo reaction. Reviews on this reaction have covered the literature up to 1987 [24-26]. The mechanism of the cycloaddition has been discussed in detail by Hoffmann [26]. 

Recently, Lautens, Aspiotis and Colucci extended the [4+3] cycloaddition methodology to include the diastereoselective intermolecular cycloaddition between an oxyallyl cation and a chiral furan [45]. The best results were obtained employing furan 26 bearing a free hydroxyl group in the 2-position, reacting with excess 1,3-dibromopentanone in the presence of diethyl zinc. Under the optimized conditions, up to 80% yield of the crystalline oxabicyclo[3.2.1]octene 27 was obtained with a diastereoselectivity of a 19 1. The other product was the minor diastereomer 28, Eq. 17. 

N-Octadecane Octahydro-4,7-methano-1 H-indenecarbaldehyde y-Octalactone n-Octanal Octanal dimethyl acetal Octanal ethyleneglycol cyclic acetal 2-Octanol 3-Octanol 3-Octanone 2-Octenal trans-2-Octenal 1-Octen-3-ol 1-Octen-3-yl acetate Octyl acetate 3-Octyl acetate Octyl butyrate Octyl formate Octyl isobutyrate Opopanax gum Orange (Citrus aurantium dulcis) peel wax Origanum oil 3-Oxabicyclo [10.3.0] pentadec-6-en Oxalide Palmarosa (Cymbopogon martini) oil Pennyroyal (Mentha pulegium) extract... 

Novotny et al. (293) identified a volatile substance in male mouse (Mus musculus) urine, whose concentration depends on the level of testosterone, as 7-exo-ethyl-5-methyl-6,8-oxabicyclo-[3.2.1]-3-octene (65) or ejco-3,4-dehydrobrevicomin, and suggested that it might be a pheromone or pheromone adjuvant. The proposed structure is identical, except for the 3,4 double bond, with that of the pine bark beetle Dendroctonus frontalis pheromone exo-brevicomin (66). 

Kozmin has reported the formation of polyqrclic ethers via the gold(I) or gold(III)-catalyzed tandem enyne cydization/alkoxylation of 1,5-enynes that contained a tethered hydroxy group [126]. As an example, treatment of homopropargyUc alcohol 86 with a catalytic 1 1 mixture of (PPhs) AuCl and AgC104 at 20 °C led to isolation of 6-oxabicyclo[3.2.1]octene 87 in 89% yield (Scheme 12.15). Conversion of 86 to 87 presumably occurs via attack of the pendant alkene on a goldhydroxy group at the disubstituted alkenyl carbon atom. Protodeauration then releases heterocycle 87 (Scheme 12.15). 

O 22 l-Octene-2-carboxylic acid. See Acrylic acid, 2-hexyl-, 0 23 7-Oxabicyclo [410] heptane, polyether O 24 Oxacyclobutane. See Oxetane. 

Derivatives of l-cyclohexylhydroxymethyl-2,4-dimethyl-8-oxabicyclo[3.2.1]octen-3-ol (13) can be ring opened to produce substituted cycloheptenes (14) in a highly regio- and stereo-selective reaction, the reagent being MeLi in the presence of Ce(III) chloride. ... 

X-Ray and n.m.r. studies on trans-cyclo-octene, 9,9-dibromo-trons-bicyclo-[6,1,0] nonane, frans-bicyclo[6,l,0]nonane, and trans-9-oxabicyclo[6,l,0]non-ane suggest that all adopt the distorted crown conformation. The last named compound is obtained, together with a small amount of its cis-isomer, on epoxidation of trans-cyclo-octene. 

Oxymercuration-demercuration of 5,6-epoxy- and 4,5-epoxy-cyclo-octenes leads largely to CTido-9-oxabicyclo[3.3 l]nonan-2-ol. Cyclo-oct-4-enone and cyclo-oct-2-enone give largely hydroxy-ketones, whereas cyclo-oct-3-enone... 

Mihovilovic and coworkers have utilized a microbial Baeyer-Villiger oxidation to desymmetrize readily available 8-oxabicyclo[3.2.1]octene 218. Their key reaction used E. coli in a whole-cell oxidation to give multi-gram quantities of 219 in high optical purity (Scheme 59) [67], To demonstrate its utility they transformed 219 into 220, 221, and 222 thus intercepting intermediates that had previously been converted into the namral products (+)-trani-kumausyne, goniofufurone, and (+)-showdomycin. 

The first transannular [4 + 3] cycloaddition was reported by Craft and Gung in the synthesis of the oxabicyclo[3.2.1] octene ABCD ring system of cortistatins." The reaction... 

Hunt KW, Grieco PA. Oxabicyclo[3.2.1]octenes in organic synthesis-direct ring opening of oxabicyclo[3.2.1] systems employing silyl ketene acetals in concentrated solutions of lithium perchlorate-diethyl ether application to the synthesis... 

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