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Ring‐size effect in the reaction of α,ω‐dibromoalkanes with ethyl acetoacetate and its application to the synthesis of some disubstituted oxa‐ and aza‐heterocycles
Author(s) -
YongYue Lin,
XiaoGuang HiuKuang Leung Liang,
YukYee Chan
Publication year - 1990
Publication title -
chinese journal of chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.28
H-Index - 41
eISSN - 1614-7065
pISSN - 1001-604X
DOI - 10.1002/cjoc.19900080211
Subject(s) - chemistry , cyclopentane , cyclopropane , alkylation , dihydropyran , ring (chemistry) , ethyl acetoacetate , steric effects , ring size , amine gas treating , medicinal chemistry , stereochemistry , organic chemistry , catalysis
Under basic condition, β‐ketoester has two sites at which alkylation can occur. In the reaction of ethyl acetoacetate with α, ω‐dibromoalkanes ( n = 2, 3, 4), the alkylation is dependent on the ring size of the possible cyclic product formed. When n = 2 or 4, cyclopropane 3 or cyclopentane 10 was formed, respectively, as a result of two successive C ‐alkylations. However, when n = 3, dihydropyran 7 was formed, arising from a C ‐alkylation followed by an alkylation. For the last case, the formation of the six‐member ring is the driving force of the whole process. Cyclopropane 3, when treated with an aromatic amine, was transformed to dihydropyrrole 15 via the possible intermediate of cyclopropyl Shiff's base 14 . However, similar reaction was not observed for cyclopentane 10 . We attribute this phenomenon to the ring‐size effect again, as in the former case, the steric strain of the cyclopropane ring is released during the rearrangement of the Schiff's base to the final product.