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cyclooctene
Cyclooctene is a cycloalkene with an eight-membered ring. It is notable because it is the smallest cycloalkene that can exist as either the ''cis''- or ''trans''-isomer with the ''cis''-isomer more common. Its most stable ''cis'' stereoisomer can adopt various conformations, the most stable one being shaped like a ribbon;〔Ulrich Neuenschwander, Ive Hermans (Conformations of Cyclooctene: Consequences for Epoxidation Chemistry" ), ''J. Org. Chem.'', Vol. 76, p.10236 (2011)〕 its most stable ''trans''-conformer is shaped like the 8-carbon equivalent chair conformation of cyclohexane.
==''cis''-Cyclooctene==
''cis''-Cyclooctene (COE) is a substrate notoriously known for quite selectively forming the epoxide, as compared to other cycloalkenes, e.g. cyclohexene. Low amounts of radical by-products are found only. The reason for this behaviour is that allylic functionalization in ''cis''-cyclooctene is more difficult than for other cycloalkenes, because of almost orthogonal allylic C-H bonds. Therefore, if radicals are around, they rather form epoxide (via an addition-elimination mechanism) than to form allylic byproducts.〔 It is used as an easily displaced ligand in organometallic chemistry, e.g. chlorobis(cyclooctene)rhodium dimer and chlorobis(cyclooctene)iridium dimer.
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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