Catalaytic Isomerization of 1,5-Enynes to Bicyclo[3.1.0]hexenes

Abstract

Transition metal-catalyzed isomerization and rearrangement reactions of unsaturated systems provide access to structural motifs not accessible through their thermal counterparts. This is exemplified by the numerous applications of transition metal-catalyzed Alder-ene reactions of 1,6-and 1,7-enynes for the synthesis of cyclopentyl and cyclohexyl ring systems. 1 The corresponding skeletal rearrangements of simple 1,5-enynes are much less studied. Berson and co-workers conjectured that the thermal rearrangement of 1,5-enyne 1 proceeds via bicyclo[3.1.0]hexene 2 to afford toluene and triene 3 as the major constituents of a complex mixture. 2 Scattered reports of transition metal-catalyzed isomerizations of 1,5-enynes 3 exist; however, these generally employ enol ethers as the ene component. 4,5 While enols are expected to be excellent nucleophiles, 6 we were intrigued by the possibility that metal-alkyne complexes could be electrophilic enough to react even with simple olefins and catalyze processes related to the thermal rearrangement.To this end, treatment of 1,5-enyne 4 with 1 mol % palladium-(II) or platinum(II) complexes returned mainly starting material (eq 2). Both silver(I) tetrafluoroborate and triphenylphosphinegold(I) chloride failed to catalyze the rearrangement of 4. On the other hand, the combination of these two complexes 7 rapidly (5 min) and cleanly produced bicyclo[3.1.0]hexene 8 5, an olefin isomer of the proposed intermediate (2) in the thermal isomerization. In sharp contrast to the gold(I)-catalyzed cyclizations of ω-alkynyl -ketoesters, 9 none of the competing 5-exo-dig cyclization to afford an exo-methylene product was observed. Finally, gold(III) chloride also catalyzed this reaction, however, with significantly lower conversion. On the other hand, 5% AuCl 3 with 15% AgOTf gave complete conversion; however, this was accompanied by a substantial amount of decomposition.

Gold and Platinum Catalysis of Enyne Cycloisomerization

“…[39] Scheme 48 summarizes the studies of Toste and coworkers. [38] Unlike the two previous reports, which utilized exclusively C(3)-acyloxy-and hydroxy-substituted enynes, Toste and co-workers found that gold catalysis of the 1,5-enyne cycloisomerization enabled efficient conversions of enynes bearing aryl and alkyl groups at the C(3) position. In a typical experiment, subjection of enyne 219 to 1 mol % of cationic gold- In 2004, Nishibayashi and co-workers also reported a sequential reaction transforming 1,5-enyne, which was generated in situ from a propargyl alcohol, to a bicycloA C H T U N G T R E N N U N G [3.1.0]hexene skeleton by tandem Ru and Pt catalysis.…”

“…[36,37] These reports were soon followed by a communication from the Toste laboratory, describing a series of independently observed cycloiso- merizations of 1,5-enynes, which were catalyzed by cationic gold-phosphine complexes. [38] Fürstner and co-workers reported that subjection of enyne 200 to a catalytic amount of PtCl 2 in toluene at 60 8C afforded bicyclic ketone 201 in 75 % yield (Scheme 44). [36] The deuterium label in the product appeared exclusively at the C (2) The studies of Malacria and co-workers are summarized in Scheme 46 and Scheme 47.…”

Katalytische carbophile Aktivierung: Platin‐ und Gold‐π‐Säuren als Katalysatoren

“…[321,322] Sofern die neu gebildete Cyclopropylgruppe ihrerseits an der Reaktion teilnimmt [Schema 69, Gl. (2) [323] Auch die in manchen Cycloisomerisierungen von 1,5-Eninen beobachteten Cyclopentene erklären sich aus einem Mechanismus mit 1,2-Alkylverschiebung, wobei während der Ringerweiterung lediglich eine andere Bindung der Cyclopropyleinheit gebrochen wird (359!361).…”

Synthetic and Structural Studies on Indenyl Phosphine Gold Complexes and Application as Catalyst for Hydration of Alkynes

“…金的配合物催化的有机反应得到了广泛的研究, 已 经能够使许多反应在温和的条件下进行, 且具有较高的 产率和化学选择性 [9] . 目前, 金的配合物催化的反应有 烯烃炔烃的环化反应 [10] 、炔烃的氢化氨基化反应 [11] , 炔 烃的水合反应 [12] 等, 在国内也有一些关于金配合物催 化有机反应的研究, 如 Friedel-Crafts 烷基化反应 [13] , 烯 烃的胺基芳基化反应 [14] 等. 本课题组此前合成了一系 列新型茚基膦配体, 并用于钯催化 C-N 偶联反应 [15,16] , 水相中的 C-C 偶联反应 [17] 以及钌催化的醇脱氢反应 [18] 等 .…”