Synthesis of labile all-trans-7,8,7′,8′-bis-acetylenic carotenoids by bi-directional Horner–Wadsworth–Emmons condensation
作者:Belén Vaz、Noelia Fontán、Marta Castiñeira、Rosana Álvarez、Ángel R. de Lera
DOI:10.1039/c4ob02144d
日期:——
Two symmetrical C7,C8-acetylenic carotenoids have been stereoselectively prepared using a bi-directional Horner–Wadsworth–Emmons condensation of the C10-dialdehyde and C15-phosphonates.
Intramolecular [4 + 2] Cycloadditions of Benzynes with Conjugated Enynes, Arenynes, and Dienes
作者:Martin E. Hayes、Hiroshi Shinokubo、Rick L. Danheiser
DOI:10.1021/ol051372l
日期:2005.9.1
Benzynes generated by the reaction of o-(trimethylsilyl)aryl triflates with TBAT participate in intramolecular [4 + 2] cycloadditions with conjugated enynes, arenynes, and dienes to furnish highly condensed polycyclic aromatic compounds. [reaction: see text]
The stereocontrolled total synthesis of a C31-allenic apo-carotenoid, paracentrone, was achieved by the convergent C20 + C11 = C31 strategy. The key elements of our synthesis were the Pd-catalyzed cross-coupling to stereoselectively construct the conjugated polyene backbone skeleton and the designed geometrical isomerization at the central doublebond of the conjugated polyene chain. In addition, the
does not cohere with the conventional logic of metathesis, according to which macrocycles are best closed at a disubstituted olefinic site; rather, the trisubstituted C11−C12 alkene flanked by an allylic ‐OH group served as the pivot point for synthesis. This motif was attained in good yield and excellent selectivity by a sequence of alkyne metathesis, trans‐hydrostannation and cross coupling. Because
Abstract A remarkable template effect in the intramolecularradical cyclization process has been observed by the successful utilization of Lewis acid receptor, aluminum tris(2,6-diphenylphenoxide) (ATPH). The origin of this efficient template effect by ATPH would be ascribable to the well-defined reaction environment created in front of the aluminum coordination center; this enables appropriate proximity