A methodology for the synthesis of 7,12-dihydro-5H-6,12-methanodibenzo[c,f]azocines
from aromatic aldehydes and N-(methoxymethyl)-N-(trimethylsilylmethyl)benzylamine using catalysis by trifluoroacetic
and perchloric acids is described. The developed protocol was applied
for the synthesis of N-unsubstituted and N-methyl-4-aryltetrahydroisoquinolines.
Nonstabilized azomethine ylides are easily trapped by anthraquinone to form stable spiro-oxazolidines, which have an unusual ability to undergo a cycloreversion in the presence of other dipolarophiles at 120-150 °C. All tested recycloadditions with carbonyl compounds and electron-poor alkenes occurred in moderate to high yields (41-92%). Moreover, increasing the reaction temperature to 210 °C made it possible to obtain adducts with low reactive dipolarophiles.
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