2- cyclohex-1,3-diene

SYNS ACTOR Q l,4-BEi ZOQL L ONEDIOXINE 2,5-CYCLOHEX. DIENE-l,4-DIONE DIOXIME DIBENZO PQD DIOXIME-1,4-CYCLOHEXA-DIENEDIONE DIOXIME-2,5-CYCLOHEX. DIENE-l,4-DIONE G-M-F NCI-C03850 PQD QDO QUINONE DIOXIME p-QUINONE DIOXIME p-QUINONE OXIME... 

When allylic compounds are treated with Pd(0) catalyst in the absence of any nucleophile, 1,4-elimination is a sole reaction path, as shown by 492, and conjugated dienes are formed as a mixture of E and Z isomers[329]. From terminal allylic compounds, terminal conjugated dienes are formed. The reaction has been applied to the syntheses of a pheromone, 12-acetoxy-1,3-dode-cadiene (493)[330], ambergris fragrance[331], and aklavinone[332]. Selective elimination of the acetate of the cyanohydrin 494 derived from 2-nonenal is a key reaction for the formation of the 1,3-diene unit in pellitorine (495)[333], Facile aromatization occurs by bis-elimination of the l,4-diacetoxy-2-cyclohex-ene 496[334],... 

Conjugate addition, 34-5, 51-2,53, 132, 133 Conjugate hydroxymethylation, 59-60 Copper(n) bromide, 54 Copper([) chloride, 120 Copper(n) chloride, 120 Copper(i) cyanide, 7,52, 53 Copper(i) iodide, 54 Corey s internal quench, 104 Cyanohydrin trimethylsilyl ether, 137 Cycloaddition. 34,112 Cydobutane-l,2-dione, 135 Cyclohept-2-dione, 135 Cyclohex-2-enone, 52,123 Cyclohcxa-1,3-diene, 26 Cyclohexane carboxaldehyde, 22-3,69 73,78... 

Marvel et al. described [27] the polymerization of 5,6-dibromocyclohexa-1,3-diene 12 to poly(5,6-dibromo-l,4-cyclohex-2-ene) (13), followed by a thermally induced, solid state elemination of HBr with formation of PPP 1. The products, however, indicate several types of structural defect (incomplete cyclization, crosslinking). 

An unusual reaction was been observed in the reaction of old yellow enzyme with a,(3-unsat-urated ketones. A dismutation took place under aerobic or anaerobic conditions, with the formation from cyclohex-l-keto-2-ene of the corresponding phenol and cyclohexanone, and an analogous reaction from representative cyclodec-3-keto-4-enes—putatively by hydride-ion transfer (Vaz et al. 1995). Reduction of the double bond in a,p-unsaturated ketones has been observed, and the enone reductases from Saccharomyces cerevisiae have been purified and characterized. They are able to carry out reduction of the C=C bonds in aliphatic aldehydes and ketones, and ring double bonds in cyclohexenones (Wanner and Tressel 1998). Reductions of steroid l,4-diene-3-ones can be mediated by the related old yellow enzyme and pentaerythritol tetranitrate reductase, for example, androsta-A -3,17-dione to androsta-A -3,17-dione (Vaz etal. 1995) and prednisone to pregna-A -17a, 20-diol-3,ll,20-trione (Barna et al. 2001) respectively. 

Reduction of aromatic compounds to dihydro derivatives by dissolved metals in liquid ammonia (Birch reduction) is one of the fundamental reactions in organic chemistry308. When benzene derivatives are subjected to this reduction, cyclohexa-1,4-dienes are formed. The 1,4-dienes obtained from the reduction isomerize to more useful 1,3-dienes under protic conditions. A number of syntheses of natural products have been devised where the Birch reduction of a benzenoid compound to a cyclohex-1,3-diene and converting this intermediate in Diels-Alder fasion to polycyclic products is involved (equation 186)308f h. 

The Birch reduction has been used by several generations of synthetic organic chemists for the conversion of readily available aromatic compounds to alicyclic synthetic intermediates. Birch reductions are carried out with an alkali metal in liquid NH3 solution usually with a co-solvent such as THF and always with an alcohol or related acid to protonate intermediate radical anions or related species. One of the most important applications of the Birch reduction is the conversion of aryl alkyl ethers to l-alkoxycyclohexa-l,4-dienes. These extremely valuable dienol ethers provide cyclohex-3-en-l-ones by mild acid hydrolysis or cyclohex-2-en-l-ones when stronger acids are used (Scheme 1). 

A structural requirement for the asymmetric Birch reduction-alkylation is that a substituent must be present at C(2) of the benzoyl moiety to desymmetrize the developing cyclohexa-1,4-diene ring (Scheme 4). However, for certain synthetic applications, it would be desirable to utilize benzoic acid itself. The chemistry of chiral benzamide 12 (X = SiMes) was investigated to provide access to non-racemic 4,4-disubstituted cyclohex-2-en-l-ones 33 (Scheme 8). 9 Alkylation of the enolate obtained from the Birch reduction of 12 (X = SiMes) gave cyclohexa-1,4-dienes 32a-d with diastereoselectivities greater than 100 1 These dienes were efficiently converted in three steps to the chiral cyclohexenones 33a-d. 

Diels-Alder reactions of 4-heteromethylene-5(4/7)-oxazolones have been described. ( )-4-(Chloromethylene)-5(4//)-oxazolone 737 reacts with 2,3-dunethyl-butadiene in the presence of ethylaluminum dichloride to afford the cycloadduct 738. The cycloaddition reaction is characterized by high diastereoselectivity and occurs without appreciable isomerization of the dienophile. Further synthetic transformations of 738 yield 1-amino-3,4-dimethyl-6-hydroxy-cyclohex-3-enecar-boxylic acid 739 (Scheme 1.121) Examples of Diels-Alder reactions of acyclic dienes and unsaturated 5(4//)-oxazolones are shown in Table 7.50 (Fig. 7.61). 

Antimony(V) fluoride reacts with almost all common solvents. For this reason the fluo-rination of hexachlorobenzene with antimony(V) fluoride is carried out using antimony(V) chloride as the solvent with heating at reflux for 1 hour. The mixture of products (49 % conversion) contains 33 compounds, mainly l,2-dichloro-3,3,4,4,5,5,6,6-octafluorocyclohcx-1-cne (56 %), 1,2,4,5-tetrachloro-3,3,6,6-tetrafluorocyclohexa-1,4-diene (16%), 1,2,4,5-tet rachloro-3,3,4,5.6,6-hexafluorocyclohex-1-ene (7%), and l,2,4-trichloro-3.3.4,5,5,6,6-hcptafluoro-cyclohex-l-ene (5%).94... 

The Lewis acid-promoted tandem inter[4 + 2]/intra[3 + 2]-cycloaddition of the (fumaroyloxy)nitroalkene (124) with the chiral /i-silylvinyl ether (125) is the key step in the total synthesis of (+)-crotanecine (126), the necine base of a number of pyrrolizidine alkaloids (Scheme 46).237 The tandem inter[4 + 2]/intra[3 + 2]-cycload-ditions of nitroalkenes (127) with dipolarophiles attached to the /f-carbon of a vinyl ether (128) provides a method of asymmetric synthesis of highly functionalized aminocyclopentanes (129) (Scheme 47).238 trans-2-( 1 -Methyl-phenylethyl)cyclohex-anol has been developed as a new auxiliary in tandem 4 + 2/3 + 2-cycloadditions of nitroalkenes.239 The scope and limitations of the bridged mode tandem inter-[4 + 2]/intra[3 + 2]-cycloadditions involving simple penta-1,4-dienes are described in detail.240 A tandem intermolecular/intramolecular Diels-Alder cycloaddition was successfiilly used to synthesize a B/C cA-fused taxane nucleus (130) in 50% overall... 

In addition to the cyclodienes discussed above, the carboxidation of 1,3-cyclohex-adiene having conjugated double bonds was also tested. In this case, the reaction is strongly complicated by the Diels-Alder side reaction. The main part of the diene is consumed by the dimerization process, and only 25-30% is involved in the oxidation, yielding cyclic ketones. 

The addition to 1,3-dienes afforded a new class of allylboron compounds. The platinum(0)-phosphine catalysts stereoselectively yielded or-1,4-addition products 131233 234 and 133216 235 for 2,3-disubstituted butadiene, 1,3-cyclohex-adiene, and 1,3-pentadiene by Txr-coordination of a diene to a platinum catalyst (Equations (30) and (31)). In contrast, phosphine-free Pt(dba)2 resulted in the selective formation of a 1,2-addition product 134216 for 1,3-pentadiene (Equation (31)). The corresponding chiral allyl boronates were synthesized by diboration of dienes with 123 or 124.234 235... 

The allylic cyclohex-2-enyl radical has its unpaired electron delocalized over two secondary carbon atoms, so it is even more stable than the unsubstituted allyl radical. The second propagation step may occur at either of the radical carbons, but in this symmetrical case, either position gives 3-bromocyclohexene as the product. Less symmetrical compounds often give mixtures of products resulting from an allylic shift In the product, the double bond can appear at either of the positions it occupies in the resonance forms of the allylic radical. An allylic shift in a radical reaction is similar to the 1,4-addition of an electrophilic reagent such as HBr to a diene (Section 15-5). 

Photochemical electrocyclic ring-closure in a 4-electron system works well for many acvclic dienes (2.17) and related cvclic systems (2.18). The situation with conjugated trienes is more complex, and they can act as 6-e ectron systems (2.19) leading to cyclohexal, J-dienes, or as 4-electron systems (2.20) giving cyclobutenes. In addition they can undergo other photochemical reactions such as geometrical isomerization about the central double bond (which must be cis if a 6-electron electrocyclic nng-closure is to take place). 

Irradiation of the 2 1 host-guest crystals of cyclohex-2-enone 81 with the axle-wheel-type host compound (— )-5 as an aqueous suspension caused regio- and enantioselective [2 + 2] photodimerization to afford the (— )-anti-head-to-head dimer 82 of 48% ee in 75% chemical yield (Scheme 18) [86]. Similarly, solid-state photolysis of the 3 2 complex of cycloocta-2,4-dien-l-one 83 with (R,R)-( — )-4 gave the (-)-anti-head-to-head dimer 84 in moderate optical yield [87]. 

Cycloaddition of buta-1,3-diene to the C2 ligand affords 356, containing complexed cyclohex-l-en-4-yne, this time attached to an Ru3 face.538 With cyclopenta-1,3-diene, formal insertion of one of the C2 carbons into a C=C double bond occurs (possibly via a three-membered ring and ringopening) to give 357.539 Two molecules of the cyclic diene have been incorporated into the organic ligand, which shows C=C double bond disorder. 

SYNS CYCLOHEX-l-ENE-l-METHANOL, 4-(l -METH-YLETHENYL)- DIHYDROCUMINYL ALCOHOL 4-ISOPROPENYL-CYCLOHEX-l-ENE-l-METHANOL p-MENTHA-l,8-DIEN-7-OL PERILLOL PERJLLYL ALCOHOL... 

Guingant and Barreto [53] published the pioneering paper describing the synthesis of ochromycinone (35) by a Diels-Alder reaction. The dienone (46) was prepared from 3-ethoxy-5-methyl-cyclohex-2-enone (45) in two steps (alternatively, a diene with SPh instead of OMe could be used). The Diels-Alder reaction with juglone (47) was catalyzed with boron triacetate to overcome the somewhat poor reactivity of the electron-deficient diene 46. The primary adduct 48 could not be isolated but directly eliminated and oxidized to ochromycinone (35) (Scheme 13). 

The complex [OsHBr(CO)(PPh3)3] is effective for the selective hydrogenation of conjugated and non-conjugated dienes to monoenes, and this complex also catalyzes the hydrogenation of linear and cyclic alkenes. (-)-Carvone (9) is selectively reduced to 2-methyl-5-(l-methylethyl)cyclohex-2-en-l-one (10) or 2-methyl-5-(l-methylethyl)cyclohexanone (11), depending on the reaction conditions. ... 

Differently substituted 1,3-dienes (204) readily add to vinylidene ftii-phos-phonate (205) to give the corresponding cyclohex-3-ene-l,l-bis-phosphonates (206). With unsymetrically substituted dienes mixture of regioisomers are obtained. In some cases migration of the double bond in the primary adducts is observed (Scheme 56). ... 

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