The transition metal-catalyzed intermolecular [5+2] cycloaddition: The homologous Diels-Alder reaction
The transition metal-catalyzed intermolecular [5+2] cycloaddition: The homologous Diels-Alder reaction
复制标题
DOI：
10.1021/ja982196x
复制
发表时间：
1998-10-28
影响因子：
15
通讯作者：
Fuji, M
中科院分区：
文献类型：
--
作者：
Wender, PA;Rieck, H;Fuji, M
Cycloaddition reactions are among the most frequently used processes in organic synthesis, providing practical access to complex molecules of theoretical, technological, commercial, and medical interest, often from simple starting materials. 1 In 1959, a homologue of the Diels-Alder cycloaddition was reported2 involving the [5+ 2] cycloaddition of a vinylcyclopropane and maleic anhydride to form a seven-membered-ring product. Efforts to reproduce this reaction have, however, not been successful, 3, 4 and its extension to other simple vinylcyclopropanes has not been reported. 5 Thus far, this reaction has been limited to a few examples of conformationally constrained, heteroatom-or strainactivated substrates and activated alkynes. 6, 7 Simple vinylcyclopropanes do not react “even [with] the strongest dienophiles”. 4 In 1995, as part of our studies on [m+n] cycloadditions which in the absence of catalysts are theoretically forbidden or difficult to achieve, 8, 9 we reported the first examples of a transition metalcatalyzed intramolecular [5+ 2] cycloaddition of simple vinylcyclopropanes and alkynes. 10 This reaction has more recently been achieved with alkenes and with asymmetric catalysis. 11 We now report the first metal-catalyzed intermolecular [5+ 2] cycloadditions of simple vinylcyclopropanes and alkynes, the long sought homologue of the Diels-Alder cycloaddition, and a fundamentally new and remarkably general process for the synthesis of seven-membered rings. Our initial attempts to effect the metal-catalyzed intermolecular [5+ 2] cycloaddition failed with various vinylcyclopropanes and alkynes using Wilkinson’s catalyst (Rh (PPh3) 3Cl), even when conditions were employed for which the corresponding intramo-lecular reaction worked well. Either the starting materials did not react or under more forcing conditions the alkyne cyclotrimerized or the vinylcyclopropane isomerized. 12 A solution to these relative rate problems was fashioned from our previous observations that oxygen substitution of the vinylcyclopropane facilitates the intramolecular cycloaddition13 and that [Rh (CO) 2-Cl] 2 14 can be used to effect intramolecular [5+ 2] cycloadditions of unreactive substrates. Thus, when siloxycyclopropane 115 was treated with dimethyl acetylenedicarboxylate in the presence of [Rh (CO) 2Cl] 2 in CDCl3 at 40 C, the facile formation of a single cycloadduct 2 was observed by NMR spectroscopy. For ease of
