Octenones

Intramolecular Friedel-Crafts acylations of olefins also give cycHc a,P-unsaturated cycHc ketones. Cyclopropane fused bicyclo[5.3.0]octenones, thus obtained, were used in the preparation of the marine sesquiterpenes, africanol [53823-07-7] and dactjlol [58542-75-9] (174). 

Ogasawara and coworkers have also published a complete series of threefold anionic domino reactions, all of which are based on an initial retro-aldol process. For instance, starting from chiral bicyclo[3.2.1]octenone 2-437, a formal total synthesis of (-)-morphine (2-445) [233] has been successfully performed (Scheme 2.103) [234]. Transformation of 2-437 into the substrate 2-488, necessary for the domino reaction, was achieved in seven linear steps. The domino process was then initiated by simply refluxing a solution of 2-438 in benzene in the presence of ethy-... 

Another synthesis using in situ-prepared o-benzoquinones has been reported by Liao and coworkers [45]. These authors observed that oxidation of 2-methoxy-phenols 7-92 with DAIB in the presence of unsaturated alcohols 7-93 furnish transient o-benzoquinone monoacetal intermediates, which easily undergo an intramolecular Diels-Alder reaction to provide bicyclo[2.2.2]octenones 7-94 with high regio- and stereoselectivity, as well as in acceptable yields (Scheme 7.25). 

Diels-Alder cycloaddition of 5-bromo-2-pyrone with the electron-rich tert-butyldi-methylsilyl (TBS) enol ether of acetaldehyde, using superheated dichloromethane as solvent, has been investigated by Joullie and coworkers (Scheme 6.90) [188]. While the reaction in a sealed tube at 95 °C required 5 days to reach completion, the anticipated oxabicyclo[2.2.2]octenone core was obtained within 6 h by microwave irradiation at 100 °C. The endo adduct was obtained as the main product. Similar results and selectivities were also obtained with a more elaborate bis-olefin, although the desired product was obtained in diminished yield. Related cydoaddition reactions involving 2-pyrones have been discussed in Section 2.5.3 (see Scheme 2.4) [189]. 

Recognizing that intermediates in the [5 + 2]-reaction of VCPs and 7r-systems could be trapped with other components, Wender and co-workers reported a three-component [5 + 2 + l]-cycloaddition involving VCPs, alkynes, and CO that provide efficient access to densely functionalized bicyclo[3.3.0]octenones via a cyclooctadienone intermediate (Scheme 55).129 This reaction converts three commercially available materials to bicyclic products and creates two stereocenters and four C-C bonds. 

As indicated in Scheme 57, the formation of the secondary bicyclo[3.3.0]octenone product is thought to occur via an in situ transannular closure of the initially formed cyclooctadienone 185. In some cases, cycloctenediones and the [5 + 2]-cycloadducts are observed as minor products (Equations (33) and (34)). 

Scheme 33. Enzyme-initiated domino reaction to give bicyclo[2.2.2]octenones 164 and 165...

Another example of suprafacial migration with inversion is the rearrangement of bicyclo octenone to give again a ketone and reported by J.A. Berson (1972). 

Ehnholt et al.8 produced a broad paper covering raw materials, and in-process and final-product measurements. While the uses are primarily in the food industry, the rancidity was often caused by microorganisms. One case involved off-flavor materials being produced in drying and curing ovens. Marker compounds (concomitant) released during the breakdown process (of saturated and unsaturated compounds) were nonenal, decenal, and octenone for the unsaturated aldehydes and ketones, and nonanal, decanal, and octanone for the saturated molecules. A 10-m folded path gas cell was used with an FT-IR for measurements down to 1 Lig/m3. 

An extensive review of 4 - - 3-cycloaddition reactions has been presented. The 1,3-difluorooxyallyl intermediate obtained from l-bromo-l,3-difluoropropan-2-one undergoes 4 + 3-cycloaddition with cyclopentadiene and ftiran to give difluorobicyclo[3.2.1]octenones. The use of 4 + 3-cycloaddition reactions of cyclic oxyallyls in the synthesis of natural products has been extensively studied. The intramolecular 4 + 3-cycloaddition of allylic sulfones (111) possessing a diene in the side-chain in the presence of Lewis acids yield cycloadducts (112) in good to excellent yields (Scheme 43). ... 

Jeong described desymmetrization of dienynes, such as iV-propargyl-jY-(penta-l,4-dien-3-yl) tosylamides, by the asymmetric Ir(i)-based PK-type reaction. The corresponding vinyl-substituted bicyclo[3,3,0]-octenones were obtained with high diastereoselectivity and enantioselectivity (Equation (36)). ... 

Selectivity for the cyclopentenone formation is improved by an intramolecular version. For example, 1,6-hepta-diyne (256, X = CH2) reacts in benzene with 2molarequiv. of Bu Me2SiH to give two bicyclo[3.3.0]octenones, 257 and 258, in 14% and 63% yield, respectively, at 95 °G under GO (20 atm) pressure.When benzene is replaced by acetonitrile, 258 becomes a sole product (60% yield). On the other hand, the reaction at 25 °G gives normal silylformylation product 259 as a major component (59%) with the concomitant formation of 258 (20%) (Scheme 12). ... 

More complicated results are observed in the reaction of 4,4-dimethyl-l,6-heptadiyn-3-ol 269 with Bu Me2SiH, giving a mtKture of 270 and 271 (Equation (44)). Discrimination of the two acetylenic moieties in 269 is hard at the silylrhodation, and thus a complex mixture of regioisomers and diastereomers results. In any event, use of rhodium species as a catalyst is essential for smooth construction of bicyclo[3.3.0]-octenone frameworks. 

In sharp contrast to 1,6-diyne 256, which gives a five-membered ring with two vo-methylene bonds and then bicyclo[3.3.0]-octenones, 1,6-enyne 273 (X = G(G02Me)2) gives five-membered product 274 (X = G(G02Me)2) as a sole product under similar conditions (Equation (46)). ... 

These conditions resulted also in high selectivities when Grignard reagents with different linear alkyl chains were used, whereas the substrate scope included a variety of aliphatic linear enones (Scheme 4). Particularly noteworthy is the addition of MeMgBr (e.g. to octenone), which provides the corresponding ketones with 97-98% ee, even when only 1 mol% of catalyst is employed. ... 

The normally sluggish Diels-Alder cycloaddition between cyclohexa-1,3-diene and various enones and enals can be activated by precoordination of the diene to a jt-basic molybdenum complex TpMo(NO)MeIm(//-cyclohexadiene)].134 The 4-1-2-cycloaddition of cyclohexa-2,4-dienones with electron-deficient 2n -dienophiles produced bridged bicyclo[2.2.2]octenones. Triplet-sensitized irradiation of these bridged bicyclooctenones produced bicyclo[3.3.0]octanoids, whereas direct irradiation yielded bicyclo[4.2.0]octanes.135... 

Intramolecular Pauson-Khand reactions to prepare [3.3.0]-bicyclo-octenones from several 1,6-enynes (eq. 2.11) were reported to occur efficiently in sc C02 using a Co2(CO)8 catalyst (Jeong et ah, 1997). The reactions proceed very well regardless of the substitution pattern of... 

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