TY - JOUR AU - Xiao, Fenfen; Zhang, Qing; Wang, Yunxia; Hu, Xiangdong TI - Synthetic Studies toward Bi-linderone Lead To Unexpected 6π-Electrocyclization Reactions: A Facile Construction of Highly Congested Spiro Compounds SN - 0039-7881 SN - 1437-210X PY - 2015 JO - Synthesis JF - Synthesis LA - EN VL - 47 IS - 17 SP - 2545 EP - 2548 ET - 2015/08/11 DA - 2015/08/19 KW - alkene KW - electrocyclic reactions KW - natural products KW - spiro compounds KW - transition states AB - During synthetic studies toward bi-linderone, unexpected 6π-electrocyclizations of 4,5-dimethoxy-2-[(E)-1,3-dimethoxy-5-phenylpenta-2,4-dienylidene]cyclopent-4-ene-1,3-dione and 2-[(E)-1-hydroxy-3-methoxy-5-phenylpenta-2,4-dienylidene]-4,5-dimethoxycyclopent-4-ene-1,3-dione were observed. The cyclization of 4,5-dimethoxy-2-[(E)-1,3-dimethoxy-5-phenylpenta-2,4-dienylidene]cyclopent-4-ene-1,3-dione gave a rare example of a 6π-electrocyclization reaction that occurs readily at room temperature in the presence of silica gel. Meanwhile, the intramolecular hydrogen bonding existing in 2-[(E)-1-hydroxy-3-methoxy-5-phenylpenta-2,4-dienylidene]-4,5-dimethoxycyclopent-4-ene-1,3-dione afforded a strong contribution to the stability of the flat conformation, and this hampered the 6π-electrocyclization process. These 6π-electrocyclizations afforded a facile approach to highly congested spiro compounds. PB - © Georg Thieme Verlag DO - 10.1055/s-0034-1381054 UR - http://www.thieme-connect.de/products/ejournals/abstract/10.1055/s-0034-1381054 ER -