2- Bromo-2-cyclohexen

A flame-dried 5-mL flask was charged with catalyst (19.2 mg, 50 pmol, 5 mol%), 2-bromo-2-cyclohexen-l-one (109 pL, 1 mmol, 1 equiv), trimethylsilyl cyanide (TMSCN 0.294 mL, 2.2 mmol, 2.2 equiv) and CH2CI2 (2.0 mL). The flask was sealed with a rubber septum and Parafilm , and the reaction cooled to —78 °C and stirred for 15 min. 2,2,2-Trifluoroethanol (73 pL, 1 mmol, 1.0 equiv) was then added via syringe and the reaction stirred at —78 °C for 12 h, after which the contents of the flask were placed under high vacuum at —78 °C for 5 min to remove excess HCN (CAUTION HCN is highly toxic). After warming to r.t., the entire reaction mixture was loaded onto a silica gel column for FC. Elution (hexanes ethyl acetate, 20 1) gave the expected product as a white solid (261 mg, 95% yield, 97% ee). 

A diastereoselective synthesis of the GH ring part of ciguatoxin (30, X = O, H2) has been reported starting from 2-bromo-2-cyclohexen-l-one. The ring expansion stage is achieved by a Baeyer-Villiger reaction <97SL307>,... 

Isoxazole-fused tetrahydroxanthenes can be obtained from the reaction of substituted salicylaldehydes with 2-bromo-2-cyclohexen-l-ol in a multistep approach involving oxime formation, conversion into an oximoyl chloride, intramolecular [3 + 2] cycloaddition and elimination of HBr promoted by silver(I) carbonate (14JOC7250). 

Another potential bottleneck to be overcome is the inherent equilibrium problem associated with the coupled substrate approach to biocatalytic carbonyl reduction and in situ product removal allowed the isolation of the pure (S)-2-bromo-2-cyclohexen-l-ol in 88% yield and with 99.8% enantiomeric excess [135]. 

Stirring. The succinimide is removed by suction filtration and washed twice with 10-mI portions of carbon tetrachloride. The combined filtrate and washings are fractionally distilled at atmospheric pressure to remove the carbon tetrachloride and excess olefin (steam bath). The residue is distilled under vacuum, giving about 60 % yield of 3-bromo-cyclohexene, bp 68715 mm or 4472 mm. 

Another method for preparing alkyl halides from alkenes is by reaction with jV-brotnosuccinimide (abbreviated NBS) in the presence of light to give products resulting from substitution of hydrogen by bromine at the allylic position—the position next to the double bond. Cyclohexene, for example, gives 3-bromo-cyclohexene. 

Two simple applications may be mentioned. With cyclohexene, 3-bromo-cyclohexene is obtained in a satisfactory yield (Expt 5.68), the latter upon dehydrobromination with quinoline affords an 80-90 per cent yield of cyclo-hexa-1,3-diene (Expt 5.13). Methyl crotonate yields the valuable synthetic reagent methyl y-bromocrotonate (Expt 5.69) this latter compound permits the introduction (in moderate yield) of a four-carbon atom chain at the site of the carbonyl group by the use of the Reformatsky reaction (compare Expt 5.170) ... 

It is well known that in cyclohexan series (26, n = 6) this elimination is very difficult to perform with classical bases26). For example, to our knowledge, no satisfactory method has so far been found for preparation of 1-bromo cyclohexene from trans 1,2-dibromo cyclohexane. This apparently very simple reaction, leads only with great difficulties to the desired compound (yields are low and tedious purifications are required to obtain a pure product27)). 

Vicinal dibromides can be debrominated by certain reducing agents, including iodide ion. The stereochemical course in the case of 1,1,2-tribromocyclohexane was determined using a Br-labeled sample prepared by anti addition of Br2 to bromo-cyclohexene. Exclusive anti elimination gave unlabeled bromocyclohexene, whereas Br-labeled product resulted from syn elimination. Debromination with sodium iodide was found to be cleanly an anti elimination. ... 

Pyrimidine annulated heterocycles fused at positions 5 and 6 to uracil have been synthesized via a three-step sequence starting from uracil 23 [7]. Firstly, the reaction with 3-bromo cyclohexene gave the N-allyl-vinyl core system 24 in 80% yield. Upon heating 24 in EtOH in the presence of HCl, aza-Claisen rearrangement gave rise to the formation of the C-cyclohexenyl uracil 25 in 38% yield. Final bro-mination (—>26) and dehydroganation steps ( 27) allow one to synthesize the desired tricyclic fused uracil systems (Scheme 10.7). 

The addition of the anion of a-bromo-a-nitrotoluerie (564) to cyclohexene gave the hexahydro derivative (565) of 3-phenyl-l,2-benzisoxazole (75TL2131). An unusual hexahydro derivative (566) was produced by the bis addition of benzonitrile N-oxide to benzoquinone (67AHC(8)277). 

Direct evidence for the existence of dichlorocarbene, by trapping with a suitable substrate, was obtained by Doering and Hoffmann in 1954. Dichlorocarbene was shown to add in a characteristic manner to the double bond of cyclohexene to give dichloronorcarane (1) in 59% yield similar adducts were obtained with other olefins. Bromo-form imderwent an analogous reaction in the presence of olefins to give... 

Problem 10.6 The major product of the reaction of methvlenecyclohexane with jV-bromo-succinimide is l-(bromomethyl)cyclohexene. Explain. 

Cyclohexene 6 undergoes cyclization with hydrogen bromide in diethyl ether at 0 C to give l-bromo-6,7,8,9-tetrahydro-477-2-benzazepin-3-amine hydrobromide (7), rather than the alternative isomer, 3-broino-7,8,9,9a-tetrahydro-6//-2-bcnzazcpin-l-amine (8). 

Cyclohexanones, 2-alkyl-5 methyl-, 56 Cyclohexene, 34 Cyclohexene, 1,6-dibromo-, 34 CYCLOHEXENE, 3-METHYL-, 101 Cyclohexene, 1-phenyl- [Benzene, (1-eyclohexen-l-yl)-], 106 2-Cyclohexen-l-ol, 2-bromo-, 34 2-Cyclohexen-l-ol, 3-methyl-, 101 2-Cyclohexen-l-one, 2-allyl-3-methyl-[2-Cyclohexen-l-one, 3-methyl-2-(2-piopenyl)-], 55... 

Cyclohexen-l-one, 3-methyl-, 53, 101 Cyclohexyl bromide [Cyclohexane, bromo ], 82... 

What concerns us here are three topics addressing the fates of bromonium ions in solution and details of the mechanism for the addition reaction. In what follows, we will discuss the x-ray structure of the world s only known stable bromonium ion, that of adamantylideneadamantane, (Ad-Ad, 1) and show that it is capable of an extremely rapid degenerate transfer of Br+ in solution to an acceptor olefin. Second, we will discuss the use of secondary a-deuterium kinetic isotope effects (DKie) in mechanistic studies of the addition of Br2 to various deuterated cyclohexenes 2,2. Finally, we will explore the possibility of whether a bromonium ion, generated in solution from the solvolysis of traAU -2-bromo-l-[(trifluoromethanesulfonyl)oxy]cyclohexane 4, can be captured by Br on the Br+ of the bromonium ion, thereby generating olefin and Br2. This process would be... 

C25H3JO4 152906-16-6) see Orlistat 6 -(acetyloxy)-5-bromo-2, 3, 8, 8 a-tetrahydro-5 -meth-oxy-l -methylspiro[2-cyclohexene-l,7 (l /f)-cyclopent[i7]-isaquinolin]-4-one... 

The 5,6-disubstituted dihydropyran 2049 is converted by iodosobenzene diacetate and Me3SiBr 16 or Mc3Sil 17 in pyridine to the 3-bromo (or 3-iodo) compounds 2050 in 79 or 84% yield, respectively [198] (Scheme 12.59). Reaction of olefins such as cyclohexene (or enol ethers) with iodosobenzene diacetate, tetra-... 

Based on this information the preparation of enone was examined from the unhalogenated (VIII)(X=H). Deprotonation can be performed with n-butyl lithium in THF at 0-5 °C followed by treatment with 3-ethoxy cyclohexen-l-one, followed by an acid quench provides the same enone (XI). This deprotonation also avoids the cryogenic conditions required to prepare enone (XI) when the bromo analog is used. Pyridinium tribromide used for aromatization of enone (XI) to biaryl phenol (X) is an inexpensive reagents ( 80/kg). 

The results of the olefin oxidation catalyzed by 19, 57, and 59-62 are summarized in Tables VI-VIII. Table VI shows that linear terminal olefins are selectively oxidized to 2-ketones, whereas cyclic olefins (cyclohexene and norbomene) are selectively oxidized to epoxides. Cyclopentene shows exceptional behavior, it is oxidized exclusively to cyclopentanone without any production of epoxypentane. This exception would be brought about by the more restrained and planar pen-tene ring, compared with other larger cyclic nonplanar olefins in Table VI, but the exact reason is not yet known. Linear inner olefin, 2-octene, is oxidized to both 2- and 3-octanones. 2-Methyl-2-butene is oxidized to 3-methyl-2-butanone, while ethyl vinyl ether is oxidized to acetaldehyde and ethyl alcohol. These products were identified by NMR, but could not be quantitatively determined because of the existence of overlapping small peaks in the GC chart. The last reaction corresponds to oxidative hydrolysis of ethyl vinyl ether. Those olefins having bulky (a-methylstyrene, j8-methylstyrene, and allylbenzene) or electon-withdrawing substituents (1-bromo-l-propene, 1-chloro-l-pro-pene, fumalonitrile, acrylonitrile, and methylacrylate) are not oxidized. 

With a variety of substituted cyclohexene oxides, e.g., the 1-methyl and 3-bromo derivatives, Bellucci et al. demonstrated that the substrates in the catalytic site adopted the conformation shown in Fig. 10.29 for 10.5 (3,4M... 

The electrobromination of organics with in situ generated bromine offers a clean and relatively nonhazardous way of producing bromo-substituted products. The bromination of hexane, cyclohexene, and styrene has been studied in a mixed aqueous/DMF electrolyte system [121]. The mechanism for this process yielding... 

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