Novel [1,5] sigmatropic rearrangements of cyclohexadienones generated from Fischer carbene complexes. A new strategy for installing the C-20 angular ethyl group in Aspidospermidine alkaloids.
[formula: see text] We report here the first examples of a [1,5] sigmatropic rearrangement in a 4a-alkyl-4a-hydrocarbazol-4-one to yield a 3-alkylcarbazol-4-one with a re-aromatized indole nucleus. The reaction of 1-methyl-3-substituted-indole-2-carbene complexes 1 with terminal alkynes yields 3,4a-dialkyl-1-methoxy-9-methylcarbazol-4-ones 2. These 4a-substituted carbazolones thermally rearrange to cleanly give the more highly aromatic 3,3-dialkyl-1-methoxy-9-methylcarbazol-4-ones 3. This reaction provides a convenient entry to the Aspidosperma family of alkaloids, which contain a 3,3-disubstituted carbazole nucleus.
Quinn
J F
JF
Department of Chemistry, Searle Chemistry Laboratory, University of Chicago, Illinois 60637, USA.
Bos
M E
ME
Wulff
W D
WD
D000470:Alkaloids / Q000138:chemical synthesis*; D000478:Alkylation; D003512:Cyclohexanones / Q000737:chemistry*; D010944:Plants / Q000737:chemistry*
D000470:Alkaloids; D003512:Cyclohexanones