A ring-closing metathesis approach to eight-membered benzannelated scaffolds and subsequent internal alkene isomerizations

• DOI: 10.1016/j.tet.2012.12.043
• Publication Date: 2012-12-29T17:34:55Z
• Authors: Abu Taher; Blessing A. Aderi...; Garreth L. Morgans; Lee G. Madeley; Setshaba D. Khanye; Leandi van der We...; Manuel A. Fernandes; Vincent J. Smith; Joseph P. Michael; Ivan R. Green; Willem A.L. van O...
• Keywords: 500; 540; 01 natural sciences; 0104 chemical sciences

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.