Tram-Cycloheptene

The method fails, however, in the attempted conversion of cycloheptene oxide (8) into tram-cycloheptene In this case, the reaction affords (trans-2-hydroxycyclo-heptyl)methyldiphenylphosphonium fluoroborate (9). 

Alternatively, ethyl A-(/J-chloroalkyl)carbamates can be obtained by the addition of ethyl N.N-dichlorocarbamate to alkenes, followed by a reduction step with sodium bisulfite or sodium metabisulfite (Na,S205). The same mixture of diastereomeric adducts (antijsyn 62 38) was obtained from (E)- and (Z)-2-butene under UV irradiation74, and the thermal addition by a radical mechanism to cyclohexene, cycloheptene, and cyclooctene was unsatisfactory because of the low yield and/or the low diastereoselectivity72,142. However, the addition to cyclopentene, indene, and acenaphthene in benzene as solvent was stereoselective in all cases the <7.s-adducts were formed initially at 0 C, but on heating the m-ad ducts or performing the reaction at 25 °C the tram-adducts were exclusively obtained142. 

Distribution measurements show that the silver complex of dr-cyclo-octene is less stable than that of cycloheptene, presumably owing to more ring strain in the latter 129,130). tronr-Cyclooctene is considerably more strained than the cis isomer, and can be separated from it by extraction with 20% aqueous silver nitrate 32), but there are no quantitative measurements of the stability of the silver complex of the tram isomer. The interesting possibility of isomerizing cis to trom-cyclooctene via metal complexes has not yet been achieved. tronr-Cyclooctene has been resolved via its platinum(II) complex with the optically active amine l-phenyl-2-amino-propane (am), 7r-CgH]4PtCl2am. 29). 

Among cycloalkenes, cyclohexenes, cycloheptenes, and cyclooctenes and their 1-methyl derivatives imdergo ci -tram-isomerization on irradiation. Trans-isomers of cyclohexenes and cycloheptenes are veiy unstable because of high ring strain and hence are isolated by trapping in hydroxyhc solvents like methanol [4]. For example, the photo-induced isomerization of cis-l-methylcyclohexene 2 to transisomer is trapped in methanol as methanol adduct [4]. 

Irradiation of cyclohexene in the presence of CuOTf produces the dimers 14 (49%) and 15 (8%), along with the cyclohexylcyclohexene 16 (24%) (Scheme 5)T The stereochemical outcome in Cu(I)-catalyzed dimerization of cyclohexene may be the result of cis-tram isomerization on irradiation of the initially formed Cu(I)-cyclohexene complex to the trans-cyclohexene-CuOTf complex 13, followed by a concerted ground state 2 + 2 cycloaddition of the highly strained tram-cyclohexene to another cyclohexene. Cycloheptene, on the other hand, produces the aU tra s-fused trimer 17 (Scheme 6) as the sole product. A 1 3 CuOTf-trans-cycloheptene complex has been proposed to be the precursor of this product. No dimerization reaction has been observed for cyclooctene and acychc olefins.However, mixed photocycloaddition occurs with cyclooctene if the other olefin is sufficiently reactive. Thus, cyclooctene adds to norbornene to produce the cyclobutane derivative 18 in 40% yield. GDdimerization was also observed when a mixture of cyclohexene and cycloheptene was irradiated in the presence of CuOTf to yield the adduct 19 (Scheme 6). ... 

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