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  • Studies of the formation of all-carbon quaternary centres, en route to lyngbyatoxin A. A comparison of phenyl and 7-substituted indole systems.

Studies of the formation of all-carbon quaternary centres, en route to lyngbyatoxin A. A comparison of phenyl and 7-substituted indole systems.

Organic & biomolecular chemistry (2004-05-12)
Janne E Tønder, Masood Hosseini, Alex B Ahrenst, David Tanner
ABSTRACT

Copper mediated allylic substitutions and conjugate additions to geranyl, cinnamyl and allylic indole compounds have been investigated with the aim of finding a method for the creation of the all-carbon quaternary centre present in the natural product lyngbyatoxin A. Reaction conditions have been found giving a 68% SN2' selectivity in the copper mediated addition of PhMgBr to geranyl chloride, as well as 99% and 95% SN2' selectivity in the copper catalysed addition of EtMgBr to cinnamyl chloride and acetate, respectively. When the optimised reaction conditions were applied to the corresponding allylic compounds containing a 7-substituted indole moiety, the regioselectivity was reversed giving only the SN2 product. The allylic indole-containing substrates were also found to be unproductive in Pd- or Mo-catalysed SN2'-type substitution reactions. In related studies, copper catalysed conjugate addition of EtMgBr to the tricyclic lactam 6-methyl-pyrrolo[3,2,1-ij]quinolin-4-one gave a maximum of 20% of the 1,4-addition product.

MATERIALS
Product Number
Brand
Product Description

Sigma-Aldrich
Ethylmagnesium bromide solution, 40% in 2-methyltetrahydrofuran
Sigma-Aldrich
Ethylmagnesium bromide solution, 1.0 M in THF
Sigma-Aldrich
Ethylmagnesium bromide solution, 1.0 M in tert-butyl methyl ether
Sigma-Aldrich
Ethylmagnesium bromide solution, 3.0 M in diethyl ether
Sigma-Aldrich
Ethylmagnesium bromide solution, 3.4 M in 2-methyltetrahydrofuran