To a stirred mixture of 58.6 g (0.5 M) of phenyl-acetonitrile and 150 g (1.5 M)
of ethyl acrylate was carefully added sodium methoxide in small increments
(about 0.1 g). The exothermic reaction was controlled by ice bath cooling to
keep the reaction mixture at 50°C. When further additions of sodium
methoxide were no longer exothermic, the reaction mixture was stirred for
one half hour more and the excess ethyl acrylate removed under reduced
pressure on a steam bath. The resulting oil was added to 1.500 g of
polyphosphoric acid and stirred on a steam bath for three hours. After cooling
to about 50°C, 0.5 liter of chloroform was added followed by additions of
crushed ice until the aqueous phase was free flowing. The chloroform layer
was separated and combined with three 150 ml chloroform extracts of the
aqueous layer. The organic phase was then dried over anhydrous magnesium
sulfate, filtered and concentrated to a semi-solid residue.
Recrystallization from acetone gave 2,3-dihydrospiro[naphthalene-1(4H),3'-
piperidine]-2',4,6'-trione, melting point 197°-199°C.
