Cir-2-Butene

Diazonium ions generated from ordinary aliphatic primary amines are usually useless for preparative purposes, since they lead to a mixture of products giving not only substitution by any nucleophile present, but also elimination and rearrangements if the substrate permits. For example, diazotization of n-butylamine gave 25% 1-butanol, 5.2% 1-chlorobutane, 13.2% 2-butanol, 36.5% butenes (consisting of 71% 1-butene, 20% fra/w-2-butene, and 9% cir-2-butene), and traces of butyl nitrites.351 ... 

Figure 16. The tranf-2-butene cir-2-butene ratios for reactions of 0 1 M 2-bro mo-butane with 0 5 M potassium t-butoxide in t-butyl alcohol in the presence of added dimethyl sulfoxide at 50 0° (Bartsch et al., 1973a).

In nonprotic solvents, alkenes are stoichiometrically oxidized by V -peroxo complexes to epoxides and consecutive oxidative cleavage products in a nonstereoselective fashion. For example, cir-2-butene gave an approximately 2 1 mixture of cis- and trans-epoxides (equation 37). The reactivity of alkenes increases with their nucleophilic nature. Alkenes containing phenyl substituents such as styrene, a- and j8-methylstyrene are also very reactive and mainly give oxidative cleavage products. 

This is a modification of the Robinson annulation in which l,3-dichloro-cir-2-butene is used in place of methyl vinyl ketone. 

Kinetics of the coisomerization of cir-2-butene-<4)/rf8 gives an insight as to whether the active sites on SiOi —Mo03 MoOa and are acidic or basic. 

Diacetates of 1,4-butenediol derivatives are useful for double allylation to give cyclic compounds. l,4-Diacetoxy-2-butene (126) reacts with the cyclohexanone enamine 125 to give bicyclo[4.3.1]decenone (127) and vinylbicy-clo[3.2.1]octanone (128)[85,86]. The reaction of the 3-ketoglutarate 130 with cir-cyclopentene-3,5-diacetate (129) affords the furan derivative 131[87]. The C- and O-allylations of ambident lithium [(phenylsulfonyl)methylene]nitronate (132) with 129 give isoxazoline-2-oxide 133, which is converted into cis-3-hydroxy-4-cyanocyclopentene (134)[88]. Similarly, chiral ds-3-amino-4-hyd-roxycyclopentene was prepared by the cyclization of /V-tosylcarbamate[89],... 

Problem 13.38 Give the hydroboration-oxidation product from (a) cydohexene, (6) cir-2-phenyl-2-butene, (c) trarw-2-phenyl-2-butene. 

Carbenes or carbenoids have also been reported to deoxygenate epoxides. To generate these species, dimethyl diazomalonate/rhodium(II) acetate and 9-diazofluorene 44 have been employed both reagents show high stereoselectivity. For example, ciJ-2-butene oxide is converted to cir-alkene with more than 93% retention under irradiation (350 nm) using 9-diazofluorene, and functional groups, such as carbonyl, can survive using diazomalonate and rhodium(II) acetate (equation 49). 

Monobromocyclopropanes (cf. 1,253 2,134 4,153). The carbenoid reagent derived from diethylzinc and bromoform in the presence of oxygen converts olefins into monobroniocyclopropanes in 70-85% yieid. Little reaction occurs in the absence of O2. syn-Isomers are formed selectively. In the reaction with cir-butene-2 only traces of the cnf/-isomer were detected by glc. 

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