The preparation and some chemistry of 2,2-dimethyl-1,2-dihydroquinolines

The cyclisation of N-(1,1-dimethylpropargyl) anilines, using cuprous chloride in refluxing toluene, yields 6-substituted-2,2-dimethyl-1,2-dihydroquinolines. The reactivity of the double bond in the heterocyclic ring of these products is exemplified by chlorination, to yield 6-substituted-3,4-cis-dichloro-2,2-dimethyl-1,2,3,4-tetrahydroquinolines which can be selectively dechlorinated to provide 6-substituted-3-chloro-2,2-dimethyl-1,2,3,4-tetrahydroquinolines; epoxidation to yield an epoxide, which can be hydrogenolysed to the corresponding 3-hydroxy product and in turn oxidised to the 3-keto derivative; and oxymercuration to provide a 4-hydroxy product and hence a 4-keto derivative. Dehydrochlorination of a 3,4-dichloro product provides a 3-chloro-1,2-dihydroquinoline which can be hydrolysed to a 3-keto system. The formation of cis 3,4-dichloro products from the chlorination, as well as the formation of a cis chlorohydrin from the chlorination of N-acetyl-2,2,6-trimethyl-1,2-dihydroquinoline in partially aqueous solution, suggests that N-acetyl, or N-trifluoroacetyl groups, participate in the addition process.