88018-04-6Relevant articles and documents
Intramolecular Cycloadditions with Carbonyl Ylides: From Oxiranes to Large Ring Systems
Brokatzky-Geiger, Juergen,Eberbach, Wolfgang
, p. 2157 - 2192 (2007/10/02)
Within the classes of 1,3-dipoles intramolecular cycloaddition reactions with carbonyl ylides, accessible by heating of the oxirane precursors 4-10, are studied for the first time in a systematic manner.Although the formation of the corresponding fused and/or bridged tetrahydrofuran derivatives (32-34, 44-46, 50-63) has been established in all cases with the exception of 4e and 6a, the rate of formation as well as the yield of the cycloadducts depend strongly on the dipolarophilicity of the olefinic component: Whereas non-activated C=C bonds undergo the cycloaddition step slowly and only when being arranged in a relatively close position to the dipole unit (the maximum size of the second ring, formed by "tieing": 9-membered), ene-oxiranes with an electron deficient double bond are reacting much faster and (in contrast to cycloadditions so far known for other 1,3-dipoles) also at a large distance between the ?-centers.In this way macrocycles with up to 34 ring members have been obtained.This high regio- and stereoselectivity observed in most cases of the cycloadditions is explained mainly by steric factors.
