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Cycloadditions of Allyl Cations, 26 1) Norbornene Derivatives from Cyclopentadiene and 2,4‐Dimethyl‐3‐penten‐2‐ol in an Acidic Two Phase System. A Stepwise Diels‐Alder‐like Cyclization
Author(s) -
VathkeErnst Heidrun,
Hoffmann H. M. R.
Publication year - 1981
Publication title -
chemische berichte
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.667
H-Index - 136
eISSN - 1099-0682
pISSN - 0009-2940
DOI - 10.1002/cber.19811140423
Subject(s) - chemistry , cyclopentadiene , norbornene , bicyclic molecule , medicinal chemistry , diels–alder reaction , organic chemistry , stereochemistry , catalysis , monomer , polymer
2,4‐Dimethyl‐3‐penten‐2‐ol ( 1 ) and cyclopentadiene react in an acidic two phase system at 0‐25°C in several steps yielding epimeric norbornenylcarbinols ( endo ‐ 4 and exo ‐ 4 ) and at least three isomeric allylcyclopentenols ( 2a, b , c ), whereas allylcyclopentadienes ( 3a , b ) and norbornene‐type olefins (endo ‐ 5 , exo ‐ 5 , and 6 ) are formed in traces under these conditions. All bicyclic products of this reaction were synthesized independently. On subjecting the pure product norbornenylcarbinols ) endo ‐ 4 and exo ‐ 4 ) to the acidic, two phase reaction conditions at slightly elevated temperature, i. e. 50°C, some epimerization occurs and the norbornene‐type olefins ( exo ‐ 5 , endo ‐ 5 , and 6 ) are mainly formed in addtion to allylcyclopentadienes ( 3a , b ) allylcyclopentenols ( 2a, b , c ), nortricyclic alcohol 7 , and tricyclic ether 8 . Independently, the forward reaction was traced by subjecting the isomeric allylcyclopentenols 2b , c to the acidic, two phase reaction conditions at 50°C: once again, endo / exo bicyclization gave the olefins 5 and 6 as well as alcohols 4 and 7 Hence, a stepwise Diels‐Alder‐like cyclization is proposed to account for the norbornenetype alcohols and bicyclic olefins, which are formed from the acid promoted reaction of cyclopentadiene and 1 .