It can be prepared in several different ways: 1) The acylation of p-anisidine (I) with cyclopropanecarboxylic acid (II) by means of ethyl chloroformate and triethylamine gives N-cyclopropanecarbonyl-p-anisidine (III), which is reduced with LiAlH4 in THF yielding N-cyclopropylmethyl-p-anisidine (IV). The reaction of (IV) with sodium cyanate in acetic acid affords N-cyclopropylmethyl-N-(p-anisyl)urea (V), which is cyclized with benzaldehyde (A) by means of methanesulfonic acid in refluxing toluene giving 1-cyclopropylmethyl-4-phenyl-6-methoxy-3,4-dihydro-2(1H)-quinazolinone (VI) (1). Finally this product is dehydrogenated by oxidation with KMnO4 in dioxane - water (1), by treatment with Cl2 or Br2 with or without a base (2), or by treatment with sulfur in refluxing o-dichlorobenzene (3).
2) The alkylation of 2-amino-5-methoxybenzophenone (VII) with cyclopropylmethyl chloride (B) by means of NaH in THF gives 2-cyclopropylmethylamino-5-methoxybenzophenone (VIII), which by reaction with ethylchloroformate (C) at 100 C yields 2-(N-cyclopropylmethylethoxycarbonylamino)-5-methoxybenzophenone (IX). Finally this compound is cyclized with ammonium acetate and KOH in DMSO at 130 C (4). 3) The oxidation of 1-cyclopropylmethyl-3-phenyl-5-methoxyindole-2-carboxylic acid (2-carboxylic acid ethyl ester, or 2-carbonitrile) (Xa-c) with CrO3 in acetic acid - water gives 2-(N-cyclopropylmethyloxalylamino)-5-methoxybenzophenone (or ethoxalylamino or cyanocarbonylamino) (XIa-c), which can be hydrolyzed to the free amine (VIII) with KOH in DMSO - water (5). 4) The amine (VIII) can also be cyclized with potassium cyanate in hot acetic acid (5,6). 5) The amine (VIII) can also by cyclized by reaction with oxalyl chloride, followed by a treatment with sodium azide in acetone - water (7).