Cyclohexadiene, reaction with

More interesting were the results obtained in reactions of 99 with acyclic dienes catalyzed by Eu(fod)3 (-20°C) and TiCl4 (-78°C). The resulting adducts 100 are unstable and underwent spontaneous sulfinyl elimination at room temperature, affording cyclohexadienes. Reactions with dienes lacking substituents at C-1 (butadiene, 2-methyl butadiene and 2,3-dimethyl butadiene) yielded optically pure compounds 101 (Scheme 49). These results indicate that the regio-selectivity and the 7r-facial selectivity of the cycloadditions are complete (only one adduct is formed) under both catalytic conditions. Desulfinylation of 100 is also completely regioselective. 

BenZotrichloride Method. The central carbon atom of the dye is supphed by the trichloromethyl group from iJ-chlorobenzotrichloride. Both symmetrical and unsymmetrical triphenyhnethane dyes suitable for acryhc fibers are prepared by this method. 4-Chlorobenzotrichloride is condensed with excess chlorobenzene in the presence of a Lewis acid such as aluminium chloride to produce the intermediate aluminium chloride complex of 4,4, 4"-trichlorotriphenylmethyl chloride (18). Stepwise nucleophihc substitution of the chlorine atoms of this intermediate is achieved by successive reactions with different arylamines to give both symmetrical (51) and unsymmetrical dyes (52), eg, N-(2-chlorophenyl)-4-[(4-chlorophenyl) [4-[(3-methylphenyl)imino]-2,5-cyclohexadien-l-yhdene]methyl]benzenaminemonohydrochloride [85356-86-1J (19) from. w-toluidine and o-chloroaniline. 

Knunyants showed that such perfluoroalkenes, under forcing conditions, undergo Diels-Alder reactions with cyclic dienes such as cyclohexadiene [72] (equation 65) or furan [7J] (equation 66). 

The application of this strategy to the synthesis of chiral cyclohexadienes has been demonstrated by Kiindig. Addition of MeLi to the Cr(CO)3-complexed chiral phenyl oxazoline 43 followed by reaction with allyl bromide produced cyclohexadiene 44 in 69% yield and >98% de. ... 

To overcome these problems with the first generation Brmsted acid-assisted chiral Lewis acid 7, Yamamoto and coworkers developed in 1996 a second-generation catalyst 8 containing the 3,5-bis-(trifluoromethyl)phenylboronic acid moiety [10b,d] (Scheme 1.15, 1.16, Table 1.4, 1.5). The catalyst was prepared from a chiral triol containing a chiral binaphthol moiety and 3,5-bis-(trifluoromethyl)phenylboronic acid, with removal of water. This is a practical Diels-Alder catalyst, effective in catalyzing the reaction not only of a-substituted a,/ -unsaturated aldehydes, but also of a-unsubstituted a,/ -unsaturated aldehydes. In each reaction, the adducts were formed in high yields and with excellent enantioselectivity. It also promotes the reaction with less reactive dienophiles such as crotonaldehyde. Less reactive dienes such as isoprene and cyclohexadiene can, moreover, also be successfully employed in reactions with bromoacrolein, methacrolein, and acrolein dienophiles. The chiral ligand was readily recovered (>90%). 

Ahern and Gokel (1979) briefly mention that (jE -arenediazocyanides also react with a variety of dienes (cyclopentadiene, cyclohexadiene, butadiene, ( )-piperylene, etc.) in a [4+ 2]-cycloaddition reaction with formation of tetrahydropyridazines (Scheme 6-31). Here the two azo nitrogen atoms of the diazocyanide react as a dieneophile in a bis-aza Diels-Alder reaction. 

Norbornadienes, norbornenones and their homologs have been prepared [23, 24] by cycloaddition of cyclopentadiene (21) and cyclohexadiene (22) with l-benzenesulfonyl-2-trimethylsilylacetylene (23) and l-ethoxy-2-carbomethox-yacetylene (24). Both were efficient dienophiles in the cycloaddition processes and dienophile 23 acted as an effective acetylene equivalent (Scheme 2.12). Norbornanes and their homologs can also be attained by Diels-Alder reaction... 

Nafion-H (144), a perfluorinated resin-sulfonic acid, is an efficient Bronsted-acid catalyst which has two advantages it requires only catalytic amounts since it forms reversible complexes, and it avoids the destruction and separation of the catalyst upon completion of the reaction [94], Thus in the presence of Nafion-H, 1,4-benzoquinone and isoprene give the Diels-Alder adduct in 80% yield at 25 °C, and 1,3-cyclohexadiene reacts with acrolein at 25 °C affording 88 % of cycloadduct after 40 h, while the uncatalyzed reactions give very low yields after boiling for 1 h or at 100 °C for 3.5 h respectively [95], Other examples are given in Table 4.24. In the acid-catalyzed reactions that use highly reactive dienes such as isoprene and 2,3-dimethylbutadiene, polymerization of alkenes usually occurs with Nafion-H, no polymerization was observed. 

One 7i-bond of an aromatic ring can be converted to a cyclohexadiene 1,2-diol by reaction with enzymes associated with P. putida A variety of substituted aromatic compounds can be oxidized, including bromobenzene, chlorobenzene, " and toluene. In these latter cases, introduction of the hydroxyl groups generates a chiral molecule that can be used as a template for asymmetric syntheses. " ... 

For the asymmetric hydrosilylation of 1,3-cyclohexadiene (42) (Scheme 3-17), the enantioselectivity is higher in the reaction with phenyldifluorosilane than that with trichlorosilane or methyidichlorosilane. The reaction of 42 with phenyldifluorosilane in the presence of a palladium catalyst coordinated with ferrocenylphosphine... 

Figure 3.25 Schematic reaction coordinates for the photochemical ring opening reactions of 1,3-cyclohexadiene. (Reprinted with permission from reference [122]. Copyright (1994) American Chemical Society.)...

The reaction of benzyne with cyclohexadiene has been known for some time 4>, but although a number of steroidal cis-dienes are readily available no reactions with arynes had been reported prior to our beginning such investigations 145>. This was somewhat surprising in view of the number of reports concerning the modification of steroids by means of reactions with carbenes 146 i49) and the known Diels-Alder reactions of steroidal dienes and trienes iso.isi). 

It is not quite clear which step takes place first - the Co-catalyzed [2+2+1] cycloaddition of the outer alkyne moiety, or the Diels-Alder reaction of the diene with the inner alkyne to form a 1,4-cyclohexadiene, which then undergoes a Pauson-Khand reaction with the remaining alkyne. Recently, it has been shown that a domino reaction can also be performed using 1 mol of a 1,7-diphenyl-1,6-diyne 6/4-20 and a 1,3-diene 6/4-21 in the presence of Co/C at 150 °C under 30 atm CO, to give the polycyclic compounds 6/4-22 as sole product (Scheme 6/4.7) [282]. 

The first use of DEAZD as a dienophile was reported by Diels in 1925.50 The reaction with cyclopentadiene was highly exothermic, and gave a high yield of the Diels-Alder adduct (Eq. 1). The reaction of DEAZD with cyclohexadiene depends on the conditions (see Section III,B and also Ref. 1). 

As expected, the azaquinone C=N double bond is strongly dienophilic. This was demonstrated by reactions with several 1,3-butadienes, cyclo-pentadiene, and cyclohexadiene (Scheme 7). These reactions, carried out... 

The full reduction of 1,3-dienes with Et3SiH/TFA occurs in certain systems although the yields are only modest.231 For example, 1,3-cyclohexadiene gives a 65% yield of cyclohexyl trifluoroacetate, presumably by way of cyclohexene (Eq. 88).211 On the contrary, 1,4-cyclohexadiene fails to undergo reaction with 10 equivalents of triethylsilane and 20 equivalents of trifluoroacetic acid even after 24 hours at room temperature (Eq. 89). 

Diels-Alder reactivity of 4-aza-6-nitrobenzofuroxan 235 has been studied via reactions with cyclopentadiene, cyclohexadiene, and 2,3-dimethylbutadiene this has led to three types of Diels-Alder adducts, namely the normal Diels-Alder adducts 234, 236, a Diels-Alder hetero-adduct 238, and the di-adducts 237, 239 arising from a minor dinitroso tautomer of compound 235 (Scheme 59) <1999CC1009, 2000JOC7391>. 

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