Novel tocopherol derivatives. Part 32: On the bromination of pyrano[3,2-f]chromenes related to γ-tocopherol.
While bromination of γ-tocopherol (2) with elemental bromine affords 5-bromo-γ-tocopherol quantitatively (3), the analogous reaction of its truncated model compound, 2,2,7,8-tetramethylchromanol (2a) is known to be accompanied by side reactions and to produce hitherto unknown byproducts. These compounds originate from pyrano[3,2-f]chromene (6), a byproduct in the synthesis of model compound 2a, which affords bromochromene 7 as the major product. The reaction mechanism was shown to proceed via chromene 8 and its 1,2-dibromo addition compound 9, which eliminates HBr in an E1 process to finally afford 7. Analytical data including crystal structures of both 6 and 7 are reported.
University of Natural Resources and Life Sciences Vienna (BOKU), Department of Chemistry, Muthgasse 18, A-1190 Vienna, Austria.
Stefan
S
Böhmdorfer
Elisabeth
E
Kloser
Anjan
A
Patel
Lars
L
Gille
Kurt
K
Mereiter
Thomas
T
Rosenau