Bulletin of the Academy of Sciences of the USSR Division of Chemical Science.
Kluwer Academic Publishers-Plenum Publishers.
Vol. 19.
1970.
P. 2368-2371
Chemistry of Heterocyclic Compounds.
Латвийский институт органического синтеза Латвийской академии наук / Springer New York Consultants Bureau.
Vol. 4.
1970.
P. 205-206