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

• Published in: Tetrahedron Vol. 69; no. 8; pp. 2038 - 2047
• Main Authors: Taher, Abu, Aderibigbe, Blessing A., Morgans, Garreth L., Madeley, Lee G., Khanye, Setshaba D., van der Westhuizen, Leandi, Fernandes, Manuel A., Smith, Vincent J., Michael, Joseph P., Green, Ivan R., van Otterlo, Willem A.L.
• Format: Journal Article
• Language: English
• Published: OXFORD Elsevier Ltd 25.02.2013; Elsevier
• Subjects: Benzodiazocine; Benzodioxocine; Benzoxazocine; Chemistry; Chemistry, Organic; Isomerization; Physical Sciences; Pyridodiazocine; Ring-closing metathesis; Science & Technology; Benzodiazocine; Benzoxazocine; Benzodioxocine; Pyridodiazocine; Ring-closing metathesis; Isomerization; TANDEM CATALYSIS; MEDIUM-SIZED HETEROCYCLES; AMIDE BOND DISTORTIONS; CONFORMATION ANALYSES; NEIGHBORING GROUP PARTICIPATION; RUTHENIUM-CARBENE; DYNAMIC-BEHAVIOR; OLEFIN-METATHESIS; RCM; IN-SITU
• ISSN: 0040-4020; 1464-5416
• DOI: 10.1016/j.tet.2012.12.043

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. [Display omitted]