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Alkoxycarbonylcarbene Transfer to Semicyclic Enaminones – A Route to Cyclopenta[ b ]pyrrole and Indole Ring Systems
Author(s) -
Müller Andreas,
Maier Alexandra,
Neumann Ralf,
Maas Gerhard
Publication year - 1998
Publication title -
european journal of organic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.825
H-Index - 155
eISSN - 1099-0690
pISSN - 1434-193X
DOI - 10.1002/(sici)1099-0690(199806)1998:6<1177::aid-ejoc1177>3.0.co;2-0
Subject(s) - chemistry , carbene , dehydrogenation , indole test , pyrrole , medicinal chemistry , ring (chemistry) , adduct , alkyl , stereochemistry , catalysis , organic chemistry
Copper‐catalyzed decomposition of alkyl diazoacetates in the presence of semicyclic enaminones 1a – o leads primarily to enamino esters 2 which constitute formal products of C–C insertion of the carbene unit. In the case of N ‐methyl ( 1a – e ) and N ‐benzyl ( 1f – i ) enaminones, 2a – i are accompanied by 2,3,5,6‐tetrahydroindoles 3a – i , in which two carbene moieties are incorporated. At 250 °C, compounds 2b – e , which could not be isolated in pure form, undergo cyclocondensation to form 1,2,3,5‐tetrahydrocyclopenta‐[ b ]pyrroles 4b – e . In contrast, 2f – i can be isolated as Z , E mixtures and are transformed thermally into 4f – i only in the presence of silica gel. Carbene transfer to N ‐phenyl enaminones 1j – m and N ‐methyl enamino esters 1n , o leads only to the 1:1 adducts, enamino esters 2j – o , which do not undergo the cyclocondensation reaction under the previous conditions. Dehydrogenation of tetrahydroindoles 3c – e with tetrachloro‐ p ‐benzoquinone can be controlled to give either 1,2‐dihydroindole‐6,7‐dicarboxylates 5 or indole‐6,7‐dicarboxylates 6 .