Heating 1 for 10 min in 85% phosphoric acid at 90" C produced 5 in a 34% isolated yield. Results of GC monitoring at 80" C (Figure 1) revealed a profile consistent with at least two parallel pathways, one resulting in the fast formation of 5 in the initial period and another leading to 4, presumably via the intermediate 2. The monoacid 2 can be isolated from the reaction mixture after heating for 20 min at 80" C. However, neither of the possible ...
