Boron trifluoride-induced, new stereospecific rearrangements of chiral epoxy ethers. Ready access to enantiopure 4-(diarylmethyl)-1,3-dioxolanes and 4,5-disubstituted tetrahydrobenzo[c]oxepin-4-ols.
Upon treatment with BF3.Et2O at low temperature, enantiopure benzyl-type ethers of arylglycidols with electron withdrawing substituents at the skeletal aryl group and electron donating substituents at the benzyl group undergo stereospecific rearrangements of Friedel-Crafts type, leading to enantiopure 4-diarylmethyl-1,3-dioxolanes (2) or to enantiopure trans-4,5 disubstituted tetrahydrobenzo[c]oxepin-4-ols (5). The course of the reactions is controlled by the substitution pattern at the benzyl ether: While benzylic systems activated toward ipso substitution afford diarylmethanes 2 through a Friedel-Crafts reaction followed by fragmentation, benzylic systems activated toward ortho attack lead to enantiopure oxepinols 5 through a 7-endo-tet ring closure of Friedel-Crafts type.
Departament de Química Orgànica and Parc Científic de Barcelona, Universitat de Barcelona, 08028 Barcelona, Spain.
Gabriela
G
Islas-González
Jordi
J
Benet-Buchholz
Miguel A
MA
Maestro
Antoni
A
Riera
Miquel A
MA
Pericàs
D001555:Benzene Derivatives / Q000737:chemistry; D001880:Boranes / Q000737:chemistry; D004148:Dioxolanes / Q000138:chemical synthesis*; D004852:Epoxy Compounds / Q000737:chemistry; D004987:Ethers / Q000737:chemistry; D010082:Oxepins / Q000138:chemical synthesis*; D013237:Stereoisomerism
D001555:Benzene Derivatives; D001880:Boranes; D004148:Dioxolanes; D004852:Epoxy Compounds; D004987:Ethers; D010082:Oxepins; C021274:boron trifluoride