Substituent Effects in the Intramolecular Diels−Alder Reaction of 6-Furylhexenoates

Abstract

The series of furyl enone esters, 4a−c, were synthesized from furan or furfural by straightforward routes. Their thermal intramolecular Diels−Alder reactions to give the tricyclic ketones 5a−c were studied in acetonitrile and toluene at two temperatures and the kinetics of the reactions determined. A comparison of these data with that obtained for the corresponding esters 2 to give the lactones 3 indicates that the rate enhancements seen for the esters (rate of dimethyl 310 times that of monomethyl) are much larger than those seen for the ketones (rate of dimethyl 6.8 times that of monomethyl). Thus, this is additional evidence for the earlier hypothesis that the presence of the oxygen atom in the tether is a factor responsible for the larger than normal rate enhancements.

Rates of Hexadehydro-Diels–Alder (HDDA) Cyclizations: Impact of the Linker Structure

“…These carbonyl functional groups affect both the electronic character of the diynophile (in this series, the monoyne) as well as the population of the reactive conformation 10 (cf. reactive rotamer effect 11 )—the structure depicted for each of 7 – 9 . Intramolecular Diels–Alder (IMDA) reactions have been reported for analogous pairs of classical triene substrates in which the only difference was the presence of an amide vs an ester 10 or of an ester vs a ketone 11 functionality within the tether.…”

“…reactive rotamer effect 11 )—the structure depicted for each of 7 – 9 . Intramolecular Diels–Alder (IMDA) reactions have been reported for analogous pairs of classical triene substrates in which the only difference was the presence of an amide vs an ester 10 or of an ester vs a ketone 11 functionality within the tether. Those cases also showed greater reactivity of the amide over the ester and of the ester over the ketone, respectively, which is similar to what we have observed for this series of HDDA reactions.…”

Intramolecular [4 + 2] Cycloaddition of Furfurylsubstituted Homoallylamines to Allylhalides, Acryloyl Chloride and Maleic Anhydride.

“…This fact means that when the competing intramolecular [4+2] cycloaddition is possible the fivemembered rings 24 would preferably be formed compared to the sixmembered ones 25 (the entropic factor). The absence of the isomer 25* among the IMDAF products is the example of a well known qem-dialkyl effect (angle compression Thorpe-Ingold effect) or of the "reactive rotamer effect" proposed by E. Jung, both phenomena being principally the same [23][24][25].…”

Synthesis of α‐fluoro‐β‐trifluoromethyl alka‐2,4‐dienes

“…Ethyl (E)-3-iodo-2-propenoate (2c) was prepared according to the method reported in the literature [12].…”