1. G. R. Carlson, U. S. Patent 4,714,492 (1987) and references cited therein.
2. O. P. Dhingra, L. F. Lee, K. L. Spear and P. G. Ruminski, European Patent Appl. EP 276204 A2, (1988). This patent described an 8-step route to 3 from acetone dicarboxylic acid via 1.
3. Janata, V.; Nemcova, P. Czech. Patent 147,252, (1970);
4. Chem. Abstr., 1973, 78, 159448j.
5. Japan Patent 56/79668 (81/79668) (1981);