Mahendar Lodi, Satyanarayana Gedu
Department of Chemistry, Indian Institute of Technology , Hyderabad Ordnance Factory Estate Campus, Yeddumailaram 502 205, Medak District, Andhra Pradesh, India.
J Org Chem. 2014 Mar 7;79(5):2059-74. doi: 10.1021/jo402763m. Epub 2014 Feb 24.
An efficient domino Pd-catalyzed transformation of simple ortho-bromobenzyl tertiary alcohols to chromenes is presented. Their formation is believed to proceed via the formation of a five-membered palladacycle, which, in turn, involves in an intermolecular homocoupling with the second ortho-bromobenzyltertiary alcohol to yield the homo-biaryl bond followed by intramolecular C-O bond formation. Interestingly, when there is an allylic substituent on the benzylic carbon atom, a chemoselective switch was observed, which preferred intramolecular Heck coupling and gave indenols. Further, it has been confirmed that the tertiary alcohol functionality is indispensible to give the coupled products, whereas the use of primary/secondary benzylic alcohols furnished the simple carbonyl products via a possible reductive debromination followed by oxidation due to the availability of β-hydrogen(s).
本文报道了一种高效的多米诺钯催化反应，可将简单的邻溴苄基叔醇转化为色烯。据信，它们的形成过程是先形成一个五元钯环，该钯环进而与第二个邻溴苄基叔醇发生分子间均偶联，生成同联芳基键，随后形成分子内碳-氧键。有趣的是，当苄基碳原子上存在烯丙基取代基时，会观察到化学选择性转变，此时优先发生分子内Heck偶联并生成茚醇。此外，已证实叔醇官能团对于生成偶联产物是必不可少的，而使用伯/仲苄醇时，由于存在β-氢，可能会先发生还原脱溴，随后氧化，从而得到简单的羰基产物。
