A ring-closing metathesis approach to eight-membered benzannelated scaffolds and subsequent internal alkene isomerizations
2013
Tāhera, Ābu | Aderibigbe, Blessing A. | Morgans, Garreth L. | Madeley, Lee G. | Khanye, Setshaba D. | van der Westhuizen, Leandi | Fernandes, Manuel A. | Smith, V. J. (Vincent J.) | Michael, Joseph P. | Green, Ivan R. | van Otterlo, Willem A.L.
A set of eight-membered benzannelated heterocycles containing two heteroatoms (O,O, NR,NR and O,NR where R=protecting group) was synthesized by ring-closing metathesis from the corresponding ortho-bis-allyl precursors. In this manner, 7-methoxy-2,5-dihydro-1,6-benzodioxocine, 1,2,5,6-tetrahydro-1,6-benzodiazocines, 5,6-dihydro-2H-1,6-benzoxazocines and 5,6,9,10-tetrahydropyrido[2,3-b][1,4]diazocine were synthesized. A number of these compounds were then treated with the catalyst [RuClH(CO)(PPh3)3] to facilitate isomerization of the alkene into conjugation with the heteroatoms in the eight-membered ring. Quite surprisingly, an equal ratio of regioisomers was obtained, even if the heteroatoms were different.
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