Yang Yonghong, Petersen Jeffrey L, Wang Kung K
Department of Chemistry, West Virginia University, Morgantown, West Virginia 26506-6045, USA.
J Org Chem. 2003 Oct 31;68(22):8545-9. doi: 10.1021/jo035036z.
A new synthetic sequence involving the use of Ireland-Claisen rearrangement of propargylic acetates to form the corresponding benzannulated enyne-allenes followed by Schmittel cyclization to generate benzofulvene biradicals for radical cyclizations leading to polycyclic aromatic compounds was established. Treatment of 9-fluorenone (8) with the lithium acetylide 9 followed by acetic anhydride produced the propargylic acetate 10. A sequence of reactions occurred after 10 was converted to the corresponding silyl ketene acetal 11. An initial Ireland-Claisen rearrangement produced the benzannulated enyne-allene 12, which then underwent a Schmittel cyclization reaction to generate the benzofulvene biradical 13. A subsequent intramolecular radical-radical coupling then produced the formal Diels-Alder adduct 14, which in turn underwent a prototropic rearrangement to give the silyl ester 15 and, after hydrolysis, the carboxylic acid 16 in 57% overall yield from 10 in a single operation. An intramolecular acylation reaction of 16 produced the ketone 17. The carboxylic acids 24-26 were likewise prepared from the diaryl ketones 18-20, respectively. However, the intramolecular [2 + 2] cycloaddition reaction of the benzannulated enyne-allene 33 having a tert-butyl group at the allenic terminus occurred preferentially, producing the 1H-cyclobut[a]indenyl acetic acid 35 as the predominant product.
建立了一种新的合成序列，该序列涉及使用炔丙基乙酸酯的爱尔兰-克莱森重排来形成相应的苯并稠合烯炔-丙二烯，然后进行施密特尔环化以生成苯并富烯双自由基用于自由基环化，从而得到多环芳烃。用乙炔锂9处理9-芴酮（8），然后用乙酸酐反应得到炔丙基乙酸酯10。在10转化为相应的甲硅烷基烯酮缩醛11后发生了一系列反应。最初的爱尔兰-克莱森重排生成了苯并稠合烯炔-丙二烯12，然后它进行施密特尔环化反应生成苯并富烯双自由基13。随后的分子内自由基-自由基偶联反应生成了形式上的狄尔斯-阿尔德加合物14，该加合物又进行了质子转移重排，得到甲硅烷基酯15，水解后得到羧酸16，从10开始，在一次操作中总收率为57%。16的分子内酰化反应生成了酮17。羧酸24 - 26同样分别由二芳基酮18 - 20制备。然而，在丙二烯末端带有叔丁基的苯并稠合烯炔-丙二烯33的分子内[2 + 2]环加成反应优先发生，生成1H-环丁[a]茚基乙酸35作为主要产物。
