71434-68-9Relevant articles and documents
Generation and Interception of 1-Oxa-2,3-cyclohexadiene
Christl, Manfred,Braun, Martin
, p. 1939 - 1946 (2007/10/02)
The reaction of 6,6-dichloro-2-oxabicyclohexane (4a) in styrene with n-butyllithium gave mainly polystyrene and 1-chloro-1-phenylhexane (6) but afforded the tetrahydrocyclobutapyrans 5, the trapping products of 1-oxa-2,3-cyclohexadiene (3) generated from 4a, only in low yield.The unstable 6,6-dibromo-2-oxabicyclohexane (4b) was generated at -60 deg C and treated with methyllithium at -30 deg C in the presence of styrene providing the products 5 in 24percent yield.Prepared from 2,3-dihydrofuran and bromofluorocarbene in 25percent yield, exo-6-bromo-endo-6-fluoro-2-oxabicyclohexane (9) is a stable source for 3.Thus, treatment of 9 in styrene, α-methylstyrene, 1,3-butadiene, 2,3-dimethyl-1,3-butadiene, furan, and 2,5-dimethylfuran with methyllithium furnished interception products of 3 in 31 - 80percent yield. Cycloadducts, i.e. 5, 12, 13, and 15, were formed as mixtures of diastereomers with the styrenes and as main products also with the 1,3-butadienes.The furans gave cycloadducts exclusively (17 and 18), the 1,3-butadienes only to a minor extent (14 and 16). and Cycloadditions display different chemoselectivity.Whereas the former utilize the enol ether double bond, the latter take place at the double bond more remote from the oxygen.Formed from 3 as a 1:1 mixture of diastereomers, the product 5 gave a 20:1:1 mixture of exo-5, endo-5, and the structural isomer 19 on heating at 150 deg C.Thermolysis of the 1:1 mixture of 13 and 14 furnished a 2:1 mixture of 14 and the tetrahydro-1-benzopyran 20. - Key Words: Allenes, six-membered, cyclic / 1-Oxa-2,3-cyclohexadiene / 3,5,6,6a-Tetrahydro-2H-cyclobutapyrans / 4,4a,5,8-Tetrahydro-3H-2-benzopyrans / 3,5,8,8a-Tetrahydro-2H-1-benzopyran
