Cyclohexenyl bromide

Scheme132 Cathodic coupling of cyclohexenyl bromide with chromium(lll) as mediator.

Bt2 is slowly released into the reaction as it proceeds, and the concentration never builds up enough to generate the dibromide. In this example, dibenzoyl peroxide is the initiator and allylic bromlnation gives the useful cyclohexenyl bromide. 

In fact, the highest anti-Cram selectivity reported to date (96% de) was observed with the MAT-mediated addition of methylmagnesium bromide to 2-(l-cyclohexenyl)propanal3 i 36. The stereochemical outcome of this addition reaction can be explained as follows on treatment of the carbonyl compound with the large aluminum reagent, the sterically least hindered complex 9 is formed. Subsequent addition of the nucleophile from the side opposite to the bulky aluminum reagent produces the anti-Cram diastereomer preferentially. 

These results show that cyclohexenyl iodonium salt readily gives cyclohexenyl cation under poorly nucleophilic/basic conditions. When a stronger nucleophile like bromide is added to the solution of 3, 1-bromocyclohexene 13 is formed as a main product (eq 5). It is noteworthy here that the rate of the reaction is strongly retarded by the added bromide salt as a nucleophilic reagent (Figure 1), although bromide does react with the substrate to give substitution product 13.6... 

Preparation of 4-12-cvclohexenvloxv )-stvrene. A stirred mixture of 34.36g (0.096 mole) methyltriphenylphosphonium bromide and 10.75g (0.096 mole) potassium t-butoxide in 200ml dry THF is treated drop-wise with a solution of 16.16g (0.080 mole) of 4-(2-cyclohexenyl)-benzaldehyde in 30ml THF under inert atmosphere. Once the addition of aldehyde was completed, the mixture was stirred at room temperature for another 2 hours. Ether and water were then added to the reaction mixture until clearly separated phases were obtained with no solid residue. The organic layer was separated and washed three times with water, dried over magnesium sulfate and evaporated. The resulting semi-solid was triturated in 10% ethyl acetate-hexane mixture to remove most of the triphenylphosphine and the evaporated extract was purified by preparative HPLC using hexane as eluent. This afforded 9.35g (58%) of the pure monomer, which was fully characterized by H and C-NMR as well as mass spectrometry. 

A further variant is the oxidation of olefins by Mn(III) acetate in the presence of halide ions. Thus, oxidation of cyclohexene by Mn(III) acetate in acetic acid at 70°C is slow, but addition of potassium bromide leads to a rapid reaction. Cyclohexenyl acetate was formed in 83% yield.223 In contrast to what would be expected for an electron transfer mechanism, norbomene (ionization potential 9.0 eV) was unreactive at 70°C, whereas cyclohexene (ionization potential 9.1 eV) and bicyclo[3,2,l] oct-2-ene reacted rapidly. The low reactivity of norbomene can be explained, if oxidation involves attack at the allylic position... 

Cyclohexenylurethane, 736 Cyclohexenyl vinyl ketone, 860-861 Cyclohexylalkylatnines, 985 Cydohexylamine, 92, 382, 857 Cyclohexylbenzene, 68 Cyclohexyl bromide, 1195, 1248 3-Cyclohexyl-2-bromopropene, 420 Cyclohexylcarbinol, 420 Cyclohexyl chloride, 506, 623... 

The crude material reacts conjugately with phenylmagnesium bromide affording the addition product in 49% yield compared to 55% obtained using chromatographically pure 1-oxo-2-cyclohexenyl-2-carbonitrile.3... 

The cyclohexenyl ether is prepared from the bromide and K2CO3 in acetone. It is cleaved with HCl in ether (92-98% yield) and with 10% Pd/C, 10% KOH, MeOH. ... 

Kinetic results are also consistent with a mechanism involving mainly the SnV(7 pathway. Solvent effects on the rate of the reaction of 11 with bromide at [Bu4NBr] = 0.05 mol dm are rather small and tend to decrease with increasing polarity of the solvents. The effect of substituents at the leaving phenyliodonio group is also small p is about 0.75, which should be compared to the substituent effect with p = 1.8 on the solvolysis of 4-r-butyl-l-cyclohexenyl(aryl)iodonium tetrafluorobo-rates, where a vinyl cation is produced in the rate-determining step (see Scheme... 

Treatment of cyclohexenol with HBr gives the corresponding allylic bromide. Only one compound is formed because attack at either end of the allylic cation gives the same product, formation of the cyclohexenyl cation... 

Alkylation (R" = alkyl or substituted alkyl) is most satisfactorily accomplished with active halogen compounds such as allyl, benzyl, and propargyl halides, but a-halo ketones, esters, and nitriles can also be used.467,474 Treating l-(l-cyclohexenyl)pyrrolidine with allyl bromide in the presence of /V-ethyl-dicyclohexylamine as base leads to introduction of two allyl groups, i.e., formation of 2,6-diallylcyclohexanone.475 Arylation can be effected by, for example, l-chloro-2,4-dinitrobenzene (R" = 2,4-dinitrophenyl).476 A-Isobutyl-fl-butylamine477 and pyrrolidine478 have been recommended as amine components for C-alkylation by simple alkyl halides such as ethyl and methyl iodides. The following two examples are illustrative ... 

Cyclohexene-l,4-diol, 586 Cyclohexene epoxide, 71, 333, 466, 488 Cyclohexene-3-ol, 428 Cyclohexenone, 21 Cyclohexenones, 371 2-(3-Cyclohexenyl)ethanol, 637 N-Cyclohexenylmotpholine, 433 Cyclohexylamine, 230 Cyclohexylideneacetaldehydes, 357 Cyclohexylidenecyclohexane, 171 Cyclohexylidenethyl bromide, 327, 328 Cyclohexyl isocyanide, 129, 152... 

Chloro-5-(1 -Cyclohexenyl)-2-Oxo-2,3-D/hydro 1 H-Benzo(f)Diazepine-1,4 68 grams of 7-chloro-5-(1 -chlorocyclohexyl)-2-oxo-2,3-dlhydro 1 H-benzo(f)dlazeplne-1,4, 34 grams of lithium carbonate and 17 grams of lithium bromide and 340 ml of anhydrous dimethyl-formamide are placed in a three-necked flask equipped with a mechanical stirrer, immersion thermometer and a reflux condenser connected with a bubble counter. 

Cyclopentene-l-carbonitrile (7.54) also reacted with N-bromosuccinimide to give an allylic bromide, 7.55.27 Subsequent reaction with ammonia displaced the bromine and acid hydrolysis of the nitrile led to 3-aminocyclopentene-l-carboxylic acid, 7.S6. Cyclohexenyl acid derivatives have also been used. Bromination of... 

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