ISSN:
0947-6539
Keywords:
ab initio calculations
;
biosynthesis
;
porphyrinogens
;
rearrangements
;
semiempirical calculations
;
Chemistry
;
General Chemistry
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
Notes:
The [1,5]-sigmatropic rearrangements of hydrogen and other groups, such as methyl, tert-butyl, allyl, benzyl, and azafulvenium, in pyrroles and, to some extent, in furans and thiophenes, has been studied by using semiempirical and ab initio methods. These systems are used as models to explain the ring D inversion in the biosynthesis of uroporphyrinogen III and the stereoselective shift of a methyl group in the biosynthesis of vitamin B12. The difference in energy between the competing pathways of hydrogen and methyl shifts is significantly lower than for cyclopentadiene. The rearrangements are usually concerted, except for in strongly resonance-stabilized systems, such as azafulvenium cations. Furthermore, ab initio calculations of the 1,3-allylic strain for a range of substituted pyrroles has been performed, and the results compared with semiempirical data.
Additional Material:
4 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/chem.19970030407