1) The cyclization of 4-cyanophenol (I) with 3-chloro-3-methylbutine (II) by means of benzyltrimethylammonium hydroxide in methanol-CH2Cl2 gives 6-cyano-2,2-dimethyl-2H-benzo[b]pyran (III), which is treated with N-bromosuccinimide in DMSO to afford 6-cyano-trans-3-bromo-3,4-dihydro-2,2-dimethyl 2H benzo[b]pyran-4-ol (IV). Epoxidation of (IV) by means of NaOH in dioxane-water yields 6-cyano-3-(4-dihydro-3,4-epoxy-2,2-dimethyl-2H-benzo[b]pyran (V), which is finally treated with 4-aminobutyric acid (VI) and NaHCO3 in refluxing ethanol. 2) By reaction of epoxide (V) with 2-pyrrolidone (X) by means of NaH in DMSO.
The reaction of epoxide (V) with ammonia in ethanol gives 4-amino-6-cyano-3,4-dihydro-2,2-dimethyl-trans-2H-benzo[b]pyran-3-ol (VII), which is condensed with 4-chlorobutyryl chloride (VIII) by means of NaOH in CHCl3 yielding 6-cyano-3,4-dihydro-2,2-dimethyl-trans-4-(4-chlorobutyrylamino)-2H-benzo[blpyran 3-ol (IX). Finally, this compound is cyclized by means of NaH in THF.