Cyclopentane, bromo

Table 2. Percentages of Dibromocyclohexane 2h, Dibromocyclopentanone UHi, trans-1-Acetoxy-2-bromocyclohexane 2a, (OS=OAc) and trans-l-Acetoxy-2-bromo-cyclopentane 10a (OS=OAc) obtained from Solvolysis of 4 in HOAc containing 0.5 M Cyclopentene and Varying [Br ], n=0.1(LiC104), ... 

Incidentally, this represents a better route to 34 (11 %) than that shown in equation 26, since it is not complicated by concurrent formation of 35. The configuration of 34 was confirmed by catalytic hydrogenation, for this afforded a 4-bromo-cyclopentane-l,3-diol that was identical with one of the products of nms-hydroxy-bromination of 3-cyclopentenyl alcohol (Eq. 28). 

Treatment of the diester 211 (E = CC Et) with lithium IV-benzyltrimethylsilylamide, followed by aqueous acid, yields the cyclopentane derivative 212, the product of an intramolecular Michael addition (equation 104)110. 1-Methylindane is produced in moderate yield by the electrochemical reduction of o-bromo-(3-butenyl)benzene (equation 105)111. 

The reaction of a-haloketones (chloro, bromo or iodo) with alkoxide ions to give rearranged esters is called Favorskii rearrangement. For example, 2-chlorocyclohexanone is converted to the methyl ester of cyclopentane carboxylic acid by treatment with sodium methoxide in ether. 

The easy access to activated aldonolactones, as described above, led us to envisage the possibility of using co-bromo-a>-deoxy-2,3-unsaturated aldono-1,4-lactones (Sect. 3.4) as precursors for highly functionalized cyclopentanes. 

As discussed in Sect. 3.4, the synthon 20 was prepared from the dibromo-heptonolactone, which in turn was obtained from the cheap commercially available D-g(ycero-D-gM/o-heptono-l,4-lactone (Table 1). The other isomeric dibro-moheptonolactones shown in Table 1, which were prepared from the heptonates, obtained from chain extension of o-mannose and o-galactose, respectively, were also converted into unsaturated bromodeoxyheptonolactones. Finally, we obtained 2-0-acetyl-7-bromo-3,7-dideoxy-D-x7(o-hept-2-enono-l,4-lactone and the corresponding D-/yxo-isomer by the Kiliani extension of o-gulose. These substrates were all cyclized to cyclopentane lactones, stereoisomers of 65 [98]. 

In a study of C-allylation of 2-bromo-2-deoxy-pentonolactones using allyl-tributylstannane and a radical initiator, mixtures of C-2-allylated pentono-1,4-lactones were obtained [99]. This may indicate that the selectivity in the reactions discussed above is determined by the cyclopentane ring. 

An intramolecular 1,5-C,H insertion reaction was reported from substituted bromo-iodoalkane and halogen-magnesium exchange reaction (equation 24) °. Indeed, treatment of bromoiodoalkane (86) with i-PrMgCl in ether at —78°C to —20°C resulted in the formation of magnesium carbenoid 87. The 1,5-C,H insertion of 87 took place to afford a cyclopentane derivative (88) however, the yield was not satisfactory. 

Another useful route to cyclopentanes is the ring contraction of 2-bromo-cyclohexanones by a Favorskii rearrangement to give cyclopentanecarboxylic acids. If a,fi-dibromoketones are used, ring opening of the intermediate cyclopropanone leads selectively to /J,y-unsaturated carboxylic acids (S.A. Achmad, 1963, 1965 J. Wolinsky, 1965). 

The bromonium ion may be generated by other methods than direct bromination solvolytic reaction of trans-2-bromo-[(4-bromophenyl)sulphonyl]cyclohexane (36) (and cyclopentane) forms (reaction 7) the bromonium ion94 (37). If Br- is present in the reaction mixture, the generation of Br2 (and olefin) is observed (Scheme 14). This confirms the reversibility of the bromonium ion formation in the usual bromination pathway. When other olefin scavengers are present, a formal Br+ transfer is observed94. This may occur without the formation of Bit. 

Canadian workers have been exploring methods for the conversion of cheap and readily available camphor into enantiopure cyclopentane derivatives for use in terpene and steroid synthesis, e.g. 1 — 2. In a recent extension of these studies, em/o-3-bromo-4-methylcamphor 3 (0.1 mol) was... 

Of the several types of enals derivable from aldoses (see 80 and 81), the 5,6-dideoxy-hex-5-enoses are of particular significance because of the efficient cyclization to give cyclopentane derivatives that they undergo on treatment with A-alkylhydroxylamines. The reactions are spontaneous and involve intramolecular 1,3-dipolar cycloadditions undergone by intermediate nitrones. For example, compound 272, made by treatment of 6-bromo compound 271 with zinc in moist alcohol, on reaction with A-methylhydroxylamine gives the bicyclic product 273 in 80% yield (Scheme 28).256 This process gives simple access to many functionalized cyclopentanes. 

From 7-bromo-7-deoxy-D-gu/ucto-heptono-1,4-lactone, highly functionalized cyclopentanes have been prepared.102 Other reactions of aldono-lactones are discussed in Ref. 37. 

Arylboronic acids (p. 905) add to alkynes to give the substituted alkene using a rhodium catalyst. Allenes react with phenylboronic acid and an aryl iodide, in the presence of a palladium catalyst, to give a substituted alkene. 2-Bromo-1,6-dienes react with phenylboronic acid with a palladium catalyst to give a cyclopentane with an exocyclic double bond and a benzyl substituent. ... 

Cyclization by direct reduction of alkynes linked to halides is usually ineffective. Phenyl-substituted alkynes are more easily reduced than alkyl chlorides but more difficult to reduce than alkyl bromides and iodides. Simple alkynes are more difficult to reduce than any of the halides. Consequently, direct reduction of 6-bromo-l-phenyl-1-hexyne at a potential of cleavage of the C Br bond only affords 12% yield of benzylidenecyclo-pentane, whereas the corresponding chloride gives the saturated benzylcyclopentene in 45% yield [241], or at low substrate concentrations (< 2 mM) the benzylidene cyclopentane (80%) [242]. 

For example, addition of 1,3-dibromopropane to the THF solution of 8 at — 78"C formed the intermediate 9a, which cyclized, when warmed to room temperature, to yield 1-methyl-l-(l-methylethenyl)cyclopentane 13 [11]. On the other hand, an acidic workup of 9a at — 35 C gave a single monoalkylated product, 6-bromo-2,3,3-trimethyl-l-hexene 12, in 72% isolated yield. Similar chemistry was observed with 1,4-dibromobutane, except that no cyclization would occur without refluxing conditions. Interestingly, the cyclization of 9a to 13 represents a cross-coupling of an organomagnesium reagent with an alkyl bromide, which is normally observed only in the presence of certain transition metal salts or complexes [12]. 

Draw all the stereoisomers of each of the molecules (a)- e) assign configuration to stereogenic centres and say whether each stereoisomer is chiral (a) 2,3-dibromobutane (b) 2-bromo-3-chlorobutane (c) the monomethyl ester of tartaric acid (2,3-dihy-droxybutanedioic acid) (d) 2,3-difluoropentane (e) 1,3-dichloro-cyclopentane. 

Bromocyclopropanes have also been prepared in reactions involving formation of a C-Br bond at the expense of a C-O bond. When 1-ethoxy-l-trimethylsiloxycyclopropane reacted with phosphorus(III) bromide, 1-bromo-l-ethoxycyclopropane (17) was obtained in 65-75% yield. Cleavage of C-O bonds occurred when trifluoromethanesulfonyloxycyclopropane was exposed to a cyclopentane solution of tributylcetylphosphonium bromide at 70 °C bromocyclopropane (18) was obtained in 95% yield along with 3-bromopropene (5%). ... 

Bromo- 534 Cyclohexane Broino- 2451 Cyclopentane Bromomethyl- 2451 Cyclopropane... 

In both of these examples the organometallic group is locked in close proximity to the triple bond, but Ward4b has shown that such steric coercion is not necessary for the reaction. Thus 6-bromo-1 -phenyl-1 -hexyne (7) is converted into benzylidene-cyclopentane (8) in 60% yield. Ward suggests that the cyclizing species is a radical and not a carbanion ... 

Sodium, toluene dispersion of, 55, 65 Sodium p-toluenesulfinate, 57, 103 Spiro[4.n] alkenones, 58, 62 Spiro(cyclopentane-l,l -indene], 55, 94 Squalene, 56, 116 Squalene, 2,3-epoxy, 56,116 Stannic chloride, 56, 97 Steroids synthesis, 58, 85 -5016606, 55, 115 58,73 z-Stilbene, 58, 133 Styrene, 56, 35 58,43 Styrene glycol, 55, 116 Styrene glycol dimesylate, 55, 116 Succinic acid, 58, 85 Succinic anhydride, 58, 85 Succinimide, 56, 50 58, 126 Succinimide, V-bromo-, 55, 28 56,49 SULFIDE CONTRACTION, 55,127 Sulfide, dimethyl-, 56, 37 SULFIDE SYNTHESIS, 58, 143 58, 138 SULFIDE SYNTHESIS ALKYL ARYL SULFIDES, 58, 143 SULFIDE SYNTHESIS DIALKYL SULFIDES, 58, 143... 

It is prepared first by the interaction of o-chlorobenzonitrile and bromo-cyclopentane in the presence of strong alkali to yield an epoxy compound. 

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