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Formation of Cyclic ‘ ortho ’‐Anhydrides of Heptalene‐1,2‐dicarboxylic Acids
Author(s) -
Weber Roland H.,
Brügger Paul,
Arnold Wolf,
Schönholzer Peter,
Hansen HansJürgen
Publication year - 1987
Publication title -
helvetica chimica acta
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.74
H-Index - 82
eISSN - 1522-2675
pISSN - 0018-019X
DOI - 10.1002/hlca.19870700602
Subject(s) - chemistry , moiety , steric effects , nucleophile , iminium , stereochemistry , alcohol , medicinal chemistry , organic chemistry , catalysis
1‐(Alkoixycarbonyl)heptalene‐2‐carboxylic acids as well as 2‐(alkoxycarbonyl)heptalene‐1‐carboxylic acids react with the iminium salt formed from N , N ‐dimethylformamide (DMF) and oxalyl chloride, in the presence of an alcohol, to yield the corresponding cyclic ‘ ortho ’ ‐anhydrides (ψ‐esters; cf. Schemes 2,3,6 , and 8 ). When the alkoxy moiety of the acids and the alcohols is different, then diastereoisomeric ‘ ortho ’ ‐anhydrides are formed due to the non‐planarity of the heptalene skeleton. The approach of the alcohol from the β‐side is strongly favored ( cf. Scheme 5 and Table 1 ). This effect can be attributed to the bent topology of the heptalene skeleton which sterically hinders the approach of the nucleophile from the α‐side of the postulated intermediates, i.e. the charged O ‐alkylated anhydrides of type 19 ( cf. Scheme 6 ). Whereas the ‘ ortho ’‐anhydrides with four substituents in the ‘peri’ ‐positions of the heptalene skeleton are configurationally stable up to 100°, the ‘ ortho ’ ‐anhydrides with only three ‘peri’ ‐substituents slowly epimerize at 100° ( cf. Scheme 7 ) due to the thermally induced inversion of the configuration of the heptalene skeleton.