Nieto-Oberhuber Cristina, Pérez-Galan Patricia, Herrero-Gómez Elena, Lauterbach Thorsten, Rodríguez Cristina, López Salomé, Bour Christophe, Rosellón Antonio, Cardenas Diego J, Echavarren Antonio M
Institute of Chemical Research of Catalonia (ICIQ), Av. Països Catalans 16, 43007 Tarragona, Spain.
J Am Chem Soc. 2008 Jan 9;130(1):269-79. doi: 10.1021/ja075794x. Epub 2007 Dec 13.
The cyclizations of enynes substituted at the alkyne gives products of formal [4+2] cyclization with Au(I) catalysts. 1,8-Dien-3-ynes cyclize by a 5-exo-dig pathway to form hydrindanes. 1,6-Enynes with an aryl ring at the alkyne give 2,3,9,9a-tetrahydro-1H-cyclopenta[b]naphthalenes by a 5-exo-dig cyclization followed by a Friedel-Crafts-type ring expansion. A 6-endo-dig cyclization is also observed in some cases as a minor process, although in a few cases, this is the major cyclization pathway. In addition to cationic gold complexes bearing bulky biphenyl phosphines, a gold complex with tris(2,6-di-tert-butylphenyl)phosphite is exceptionally reactive as a catalyst for this reaction. This cyclization can also be carried out very efficiently with heating under microwave irradiation. DFT calculations support a stepwise mechanism for the cycloaddition by the initial formation of an anti-cyclopropyl gold(I)-carbene, followed by its opening to form a carbocation stabilized by a pi interaction with the aryl ring, which undergoes a Friedel-Crafts-type reaction.
在炔烃处被取代的烯炔与金（I）催化剂发生环化反应，生成形式上的[4+2]环化产物。1,8-二烯-3-炔通过5-外向-双环化途径环化形成氢化茚。在炔烃处带有芳基环的1,6-烯炔通过5-外向-双环化，然后进行傅克型扩环反应，生成2,3,9,9a-四氢-1H-环戊并[b]萘。在某些情况下，也会观察到作为次要过程的6-内向-双环化，不过在少数情况下，这是主要的环化途径。除了带有庞大联苯膦的阳离子金配合物外，一种含有亚磷酸三（2,6-二叔丁基苯基）酯的金配合物作为该反应的催化剂具有异常高的活性。该环化反应在微波辐射下加热也能非常有效地进行。密度泛函理论计算支持了环加成反应的分步机理，即首先形成反式环丙基金（I）-卡宾，然后其开环形成通过与芳基环的π相互作用而稳定的碳正离子，该碳正离子发生傅克型反应。
