Wu H P, Aumann R, Fröhlich R, Saarenketo P
Organisch-Chemisches Institut der Universität Münster, Germany.
Chemistry. 2001 Feb 2;7(3):700-10. doi: 10.1002/1521-3765(20010202)7:3<700::aid-chem700>3.0.co;2-d.
A cascade of cyclization/cycloaddition reactions was triggered by addition of protic oxygen nucleophiles ROH 2 (RO = CH3CO2, PhCO2, PhO) to [2-(1-cyclohexenyl)ethynyl]carbene complexes 1b and 1c (M=W, Cr, respectively), affording highly strained "dimers" 11/11' and "trimers" 12 of the carbene ligand. The first reaction step involved the formation of 1-metalla1,3,5-hexatrienes 7, which readily gave tetrahydroindenes 8 by pi cyclization and extrusion of the metal unit. "Dimers" 11/11' were generated from tetrahydroindenes 8 by a highly exo selective [4+2] cycloaddition of compounds 1b and 1c to afford 1-metalla-1,3,5-hexatriene intermediates 9, and a spontaneous pi cyclization of the latter compounds involving the disengagement of the metal unit. Propenylidene cyclohexenes 13/13' were formed in "ene"-type side reactions to the pi cyclization of 1-metalla-1,3,5-hexatrienes 7, by loss of the metal unit. "Dimers" 11 were transformed into "trimers" 12 by a [4+2] cycloaddition and subsequent pi-cyclization of the resulting 1-metalla-1,3,5-hexatriene system. The course of the reaction was elucidated by means of model reactions with (2-phenylethynyl)carbene complex 14, in which 1-metalla-1,3,5-hexatriene intermediates 16 and 17 were isolated and characterized. Alkynyl benzene derivatives 19 were obtained by an unprecedented ring-expansion of a cyclopentadiene unit of "dimers" 11a and 11c, involving the insertion of a carbene carbon atom of compound 14 into a C=C bond. A reaction cascade leading to "dimers" 24/24' could also be triggered by treatment of compounds 2 with [2-(1-cycloheptenyl)ethynyl]carbene tungsten complex 1d.
通过向[2-(1-环己烯基)乙炔基]卡宾配合物1b和1c（M分别为W、Cr）中加入质子性氧亲核试剂ROH₂（RO = CH₃CO₂、PhCO₂、PhO）引发了一系列环化/环加成反应，得到了卡宾配体的高张力“二聚体”11/11'和“三聚体”12。第一步反应涉及1-金属-1,3,5-己三烯7的形成，其通过π环化和金属单元的消除很容易生成四氢茚8。“二聚体”11/11'由四氢茚8通过化合物1b和1c的高度外型选择性[4+2]环加成生成1-金属-1,3,5-己三烯中间体9，并由后者化合物自发进行涉及金属单元脱离的π环化反应生成。亚丙基环己烯13/13'是在1-金属-1,3,5-己三烯7的π环化的“烯”型副反应中通过金属单元的损失形成的。“二聚体”11通过[4+2]环加成以及随后所得1-金属-1,3,5-己三烯体系的π环化反应转化为“三聚体”12。通过与(2-苯基乙炔基)卡宾配合物14进行模型反应阐明了反应过程，其中分离并表征了1-金属-1,3,5-己三烯中间体16和17。炔基苯衍生物19是通过“二聚体”11a和11c的环戊二烯单元前所未有的扩环反应得到的，该反应涉及化合物14的一个卡宾碳原子插入C=C键中。用[2-(1-环庚烯基)乙炔基]卡宾钨配合物1d处理化合物2也可以引发导致“二聚体”24/24'的反应级联。
