ISSN:
0018-019X
Keywords:
Chemistry
;
Organic Chemistry
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
Notes:
In the presence of HSO3F/Ac2O in CH2CL2, 2-exo- and 2-endo-cyano-5,6-exo-epoxy-7-oxabicyclo[2.2.1]hept-2-yl acetates (6a, b) gave products derived from the epoxide-ring opening and a 1,2-shift of the unsubstituted alkyl group (σ bond C(3)-C(4)). In contrast, under similar conditions, the 5,6-exo-epoxy-7-oxabicyclo[2.2.1]heptan-2-one (6c) gave 5-oxo-2-oxabicyclo[2.2.1]heptane-3,7-diyl diacetates 20 and 21 arising from the 1,2-shift of the acyl group. Acid treatment of 5,6-exo-epoxy-2,2-dimethoxy-7-oxabicyclo[2.2.1]heptane (6d) and of 5,6-exo-epoxy-2,2-bis(benzyloxy)-7-oxabicyclo[2.2.1]heptane (6e) gave minor products arising from epoxide-ring opening and the 1,2-shift of σ bond C(3)-C(4) and major products (25, 29) arising from the 1,3-shift of a methoxy and benzyloxy group, respectively. Under similar conditions, 5,6-exo-epoxy-2,2-ethylenedioxy-7-oxabicyclo[2.2.1]heptane (6f) gave 1,1-(ethylenedioxy)-2-(2-furyl)ethyl acetate (32, major) and a minor product 33, arising from the 1,2-shift of σ bond C(3)-C(4). The following order of migratory aptitudes for 1,2-shifts toward electron-deficient centers has been established: acyl 〉 alkyl 〉 alkyl α-substituted with inductive electron-withdrawing groups. This order is valid for competitive Wagner-Meerwein rearrangements involving equilibria between carbocation intermediates with similar exothermicities.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/hlca.19870700706
Permalink