1. E. Ziegler, G. Kollenz undH. Igel, Mh. Chem.102, 1769 (1971).
2. G. Wagner, Arch. Pharm.290, 520 (1957).
3. G. Kollenz, E. Ziegler undTh. Kappe, Mh. Chem.100, 1736 (1969).
4. R. Meyer undO. Spengler, Ber. dtsch. chem. Ges.38, 951 (1905).
5. M. Kurihara undN. Yoda, Tetrahedron Lett.1965, 2597.