1.4- Dien-3-ones

An ipso attack on the fluorine carbon position of 4-fIuorophenol at -40 °C affords 4-fluoro-4-nitrocyclohexa-2 5-dienone in addtion to 2-nitrophenol The cyclodienone slowly isomenzes to the 2-nitrophenol Although ipso nitration on 4-fluorophenyl acetate furnishes the same cyclodienone the major by-product is 4 fluoro-2,6-dinitrophenol [25] Under similar conditions, 4-fluoroanisole pnmar ily yields the 2-nitro isomer and 6% of the cyclodienone The isolated 2 nitro isomer IS postulated to form by attack of the nitromum ion ipso to the fluorine with concomitant capture of the incipient carbocation by acetic acid Loss of the elements of methyl acetate follows The nitrodienone, being the keto tautomer of the nitrophenol, aromatizes to the isolated product [26] (equation 20) Intramolecular capture of the intermediate carbocation occurs in nitration of 2-(4-fluorophenoxy)-2-methyIpropanoic acid at low temperature to give the spiro products 3 3-di-methyl-8 fluoro 8 nitro-1,4 dioxaspiro[4 5]deca 6,9 dien 2 one and the 10-nitro isomer [2d] (equation 21)... 

The irradiation of 2,5-dimethylfuran in the presence of mercury vapor gave a complex mixture of products. Carbon monoxide and propene were removed as gaseous products. Then, cis- and rran.s-l,3-pentadiene, isoprene, 1,3-dimethylcyclopropene, 2-pentyne, 2-ethyl-5-methylfuran, hexa-3,4-dien-2-one, 1-methyl-3-acetylcyclopropene, and 4-methylcyclopent-2-enone were obtained (Scheme 8) (68JA2720 70JA1824). The most abundantproduct was the cyclopentenone 19, the second was the 1,3-pentadiene 12, while the third product was the cyclopropenyl derivative 18. 

When 2,7-dimethyloxepin is treated with potassium in liquid ammonia at — 70 C, a mixture of oct-4-en-2-one (1) and octa-4,6-dien-2-one (2) in a ratio of 75 20 is obtained.203 The major product can be separated by preparative gas chromatography in 23% yield. The analogous reaction of 3-benzoxepin gives, in 30% yield, a mixture of (2-cthylphenyl)acetaldehyde (3) and (2-ethynylphenyl)acetaldehyde (4) that resists separation.203 The Latter product can be formed exclusively in 17% yield when 3-benzoxepin is treated with sodium amide in tetra-hydrofuran at 33 C for 210 minutes.203... 

It has been reported that irradiation of bicyclo[5.1.0]octa-3,5-dien-2-one (63) in methanol leads to a mixture of racemic tricyclo[4,2.0.03,5]oct-7-en-2-one (65), 37, and cyclohepta-l,3,5-triene35). Control of the reaction was also tried in expectation... 

The condensation of acetone can also occur over acidic sites as shown by a number of authors [1,9], Generally, when this occurs other products are formed such as isobutene and acetic acid, by the cracking of DAA. Additionally mesitylene can be formed by the internal 2,7-aldol condensation of 4,6-dimethylhepta-3,5-dien-2-one which is in turn obtained by the aldol condensation of MO with a deprotonated acetone molecule [7, 8], As these species are not observed we can concluded that any acidic sites on the silica support are playing no significant role in the condensation of acetone. 

Malonic acid diamide, m4 Malonylurea, bl Margaryl alcohol, hi a Mellitic acid, b20 MEM chloride, m74 Menadione, m321 1,8-Mentanediamine, d51 / -Mentha-1,8-diene, L17, L18 / -Mentha-6,8-dien-2-one, c20 Mercaptobenzene, tl 56... 

Only few examples have been reported so far on nucleophilic addition reactions to acceptor-substituted polyenes123,124,186 188. In 1933, Farmer and Martin186 examined the reaction of methyl 2,4,6-octatrienoate with sodium dimethyl malonate and isolated the 1,4-adduct as major product (equation 81). In contrast to this, 3,5,7-nonatrien-2-one and ethyl 2,4,6-octatrienoate react with organocuprates under 1,8-addition to provide the 4,6-dien-2-ones and 3,5-dienoates, respectively (equation 82)187. 

Zirconium tetrachloride promotes a tandem nucleophilic addition and aldol-type condensation reaction of methyl propynoate, or /V,/V-dimethylpropynamidc, with aldehydes, or ketones, in the presence of tetra-n-butylammonium iodide (Scheme 6.13) [8] with a high selectivity towards the formation of Z-isomers. A similar reaction occurs between aliphatic and aromatic aldehydes and penta-3,4-dien-2-one to yield 1-substituted 2-acetyl-3-iodobut-3-enols (50-75%) [9]. 

The dispersity or homogeneity of the reductant in a reaction system sometimes plays a decisive role. It is also important for synthetic practice. Crandall and Mualla (1986) compared reduction of 7-methylocta-5,6-diene-2-one [H3C-C(CH3)=C=CH-CH2-CH2-C(0)-CH3] in THF by the action of naphthalene-sodium, on the one hand and, by sonically activated sodium on the other. In both the cases, one-electron transfer yields the anion-radical salt of the allenic ketone with sodium. However, only in the case of sonicated sodium is this salt stabilized, eventually giving H3C-C(CH3)=C=CH-CH2-CH2-C(0H)-CH3 along with cyclic products (l-methyl-2-isopropylidene cyclopentanol and l-methyl-2-isopropylcyclopent-2-enol). If naphthalene-sodium is used, only the cyclic alcohols are obtained as mentioned earlier. 

Octanoate, methyl LP Octa-trans-2-cis-4-dien-l-al LP Octa- rans-2-trans-4-dien-l-al LP Octa-trans-3-cis-5-dien-2-one LP Oct-trans-2-enoic acid LP ... 

Intramolecular photoaddition in cis-5,5,6-trimethylhepta-3,6-dien-2-one (284) takes a different course,296 yielding not the oxetane but the two dihydropyrans (285 and 286). This is in contrast to the inter-molecular cycloaddition of a, jS-unsaturated aldehydes to alkenes which affords only oxetanes, and has been accounted for in terms of diradical intermediates (287 and 288) formed from the s-cis conformation (284) of the dienone. The intermolecular equivalent is thought to occur by addition to the s-trans conformation. 

Photorearrangement of aryl-6,7-dioxabicyclo[3.2.2]nona-3,8-dien-2-ones has also been reported.241... 

Keywords 4-isopropyltropolone methyl ester, inclusion crystal, [2+2]photo-cycloaddition, bicyclo[3.2.0]hepta-3,6-dien-2-one, methyl-4-oxocyclopent-2-ene-... 

A crystalline powder of the 2 1 1 complex of (—)-l, 2 and CHC13 (4.44 g) was irradiated by a 400-W high-pressure Hg-lamp (Pyrex filter) in the solid state for 70 h. Separation of the reaction mixture by silica gel column chromatography gave a mixture of (-)-5-isopropyl-7-methoxybicyclo[3.2.0]hepta-3,6-dien-2-one 3 ([a]D-207° (c 0.23, CHC13), 96% ee) and (-)-methyl-l-isopropyl-4-oxocyclopent-2-ene-l-acetate 4 ([a]D-94.6 °(c 0.10, CHC13), 90% ee). The optical purities were determined by HPLC (Chiralcel OD, Daicel). 

Baylis-Hillman (and aza-BH) reactions have been reported for /V-tosyl aldimines and aryl aldehydes with 3-methylpenta-3,4-dien-2-one, H2C=C=C(Me)COMe.174... 

A number of bicyclic ketones such as bicyclo[3.2.1]octa-3,6-dien-2-one which are both a, (3 and y, 6 unsaturated undergo photoisomerization to vinylcyclopropyl ketenes40. These reactions may be mechanistically related to the reactions of 12 and 14 however, the reactions have also been described as [3,3]-sigmatropic shifts41. ... 

Bicyclo[2.2.2]oct-5,7-dien-2-ones 57a-c, which are endowed with the structural features required for both the ODPM and DPM rearrangements, undergo acetophenone-sensitized DPM rearrangement to afford the compounds 58a-c in good yields (Scheme 4.24) [34],... 

Chang, S.-Y., Huang, S.-L., Villarante, N.R., and Liao, C.-C. (2006) Photochemical reactions of 1,3,3-trimethyl-bicyclo[2.2.2]octa-5,7-dien-2-ones. 

Zandomeneghi, M., Cavazza, M., and Pietra, F. (1984) Enantiomeric enrichment of cis-bicyclo[3.2.0]hept-3,6-dien-2-one with circularly polarized light via the photointerconversion ofthe enantiomers. Journal of the American Chemical Society, 106, 7261-7262. 

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