Cycloalkenes into esters

The full paper on the conversion of 1,2-diols into alkenes by reduction-elimination of appropriate 1,3,2-dioxaphospholans has appeared (see Organophosphorus Chemistry , Vol. 8, p. 123). 2 method was examined with particular regard to the conversion of cyclodecane- and cyclododecane-1,2-diols into the cycloalkenes, as mixtures of cis- and tmns-isomers, and consists of the treatment of the cyclic ethyl esters or AW-dimethylamides with lithium in liquid ammonia or with Ti-THF. The kinetics of the methanolysis of thiophosphoryl chlorides have been studied. The rather unusual isomerization of 2-hydroxyethyl phosphorothioates (70) yields the 2-mercaptoethyl isomers after several days at room temperature instead of the expected thiono-esters. This observation should be compared with those reported in ref. 83. 

The reduction of epoxides withborane is noteworthy as it gives rise to the less substituted alcohol as the major product (7.96), in contrast to reduction with complex hydrides (compare with Scheme 7.71). The reaction is catalysed by small amounts of sodium or lithium borohydride and high yields of the alcohol are obtained. With 1-alkylcycloalkene epoxides, the 2-alkylcycloalkanols produced are entirely cis, and this reaction thus complements the hydroboration-oxidation of cycloalkenes described in Section 5.1, which leads to trans products. Reaction with borane in the presence of boron trifluoride has also been used for the reduction of epoxides and for the conversion of lactones and some esters into ethers. 

An oxidative cleavage of cycloalkanones to unsaturated aldehyde-esters has been developed. Thus, for example, cyclononanone was converted into 2,2-dithio-trimethylenecyclononanone, which was cleaved using lead(iv) acetate (66 %), and the product so obtained treated with methanol and sodium periodate to give (208 in = 5). Cyclododecanone was similarly converted into (208 n = 8). 1,2-Bis(trimethyl-silyloxy)cycloalkenes, prepared by acyloin condensations, have been converted into 2-alkyl-2-hydroxycycloalkanones by treatment with methyl-lithium and an alkyl halide, and the oximes of these a-hydroxyketones cleaved to give open-chain co-cyanoketones using mesyl chloride-pyridine. ... 

Lewis acid, In(0CF3S02)3, catalysed allylic C—H oxidation of aryl cycloalkenes by l-(propyl thio)pyrrolidine-2,5-dione in the presence of CH2CI2 and various nucleophiles (ROH, RCO2H, RSO2NH2) resulted in the formation of allylic ethers, esters, and sulfonamides in 52-83% yields electron-rich substrates were the most reactive. Other aryl cycloalkenes such as 1-naphthyl, l-(3-thiophenyl)-cyclohexene, 1-phenylcycloheptene, and 1-phenylcyclopentene were suitable substrates. Mechanistic studies showed that the sulfenamide played an important role in converting the allyl sulfide intermediate into the products. ... 

The "allyl shift" in accordance with an Sf2 process is typical for all 2-alkenylborane or -boronate reactions with electrophiles unless ate complexes get involved. This also holds for protodeborylations. The metalation of a 2-alkene or cycloalkene with a superbase followed by condensation with a boric ester or fluorodimethoxyborane and acidification results in the "counterthermodynamic" transformation of an internal into a terminal olefin (Scheme 1-19). ... 

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