ISSN:
0018-019X
Schlagwort(e):
Chemistry
;
Organic Chemistry
Quelle:
Wiley InterScience Backfile Collection 1832-2000
Thema:
Chemie und Pharmazie
Notizen:
On the Course of the Intramolecular Diels-Alder-Reaction of Cyclopentadienes with Olefinic SubstituentsThe 1:3 mixture of 4-bromobicyclo [3.2.0]hept-2-en-6-one and -7-one (1/2), available by N-bromosuccinimide bromination of bicyclo [3.2.0]hept-2-en-6-one, reacted rapidly with the organo-magnesium and -zinc reagents 3, 10a, 10b and 10d by cyclobutanone ring opening and bromide ion expulsion to give the 5-substituted cyclopentadienes 5, 12a, 12b/12c, and 12d as non-isolated intermediates. Further transformation occured in situ either by a direct intramolecular Diels-Alder reaction (path a) or by a [1,5]-H-migration prior to the intramolecular Diels-Alder reaction (path b). The intermediate 5 followed only path a to give the bridged norbornene derivative 7, the intermediates 12a, 12b and 12c followed only path b to give the annellated norbornene derivatives 15a, 15b and 15c, respectively, and the intermediate 12d followed both paths to give the bridged 14d and the annellated norbornene derivative 15d (in the ration of about 1.4:1). These observations are discussed in terms of the relative velocities of [1,5]-H-migrations and intramolecular Diels-Alder reactions. The major conclusions are: (1) bridged norbornene derivatives with a six-membered ring C (such as 14d) can be prepared by an intramolecular Diels-Alder reaction from 5-alkenyl-cyclopentadienes 12, as long as the dienophilic double bond is activated by an appropriate substituent (as in 12d); (2) such 5-alkenyl-cyclopentadienes 12 are available from the reaction of the bromo-bicyclo-heptenones 1/2 with suitable C-nucleophiles 10.
Zusätzliches Material:
3 Tab.
Materialart:
Digitale Medien
URL:
http://dx.doi.org/10.1002/hlca.19830660630
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