Sequential Allenylidene/Vinylidene Cyclization on Ruthenium for Stereoselective Construction of Bicyclic/Tricyclic Carbocycles from Aryl Propargyl Alcohol
Date Issued
2014
Date
2014
Author(s)
Ma, Hao-Wei
Abstract
The tandem cyclization reaction of phenyl propargyl alcohol 1, in which a 2-methyl-substituted allyl group is bound to the ortho-position of the phenyl ring, is catalyzed by [Ru]NCCH3+ ([Ru] = Cp(PPh3)2Ru) in a cosolvent of CHCl3/MeOH at 60 °C, to afford the cyclized compound 15a with two newly formed six-membered rings. In CHCl3 the catalytic reaction by [Ru]NCCH3+ stops at the isolable organic cyclization intermediate enyne 7. The first part of this tandem cyclization proceeds via an allenylidene complex B followed by a C-C bond formation between Cγ of the allenylidene ligand and the terminal carbon atom of the vinyl group generating the vinylidene complex 3, which can be isolated if [Ru]Cl is used. The presence of the methyl group on the internal vinyl carbon may serve to stabilize a proposed carbocation making the cyclization possible. The second part of the cyclization, which requires the presence of methanol, proceeds via addition of the olefin moiety on the six-membered ring to Cα of the vinylidene ligand of 3. This is followed by a demetalation process, affording the final product 15a. Tandem cyclization of analogous phenyl propargyl alcohol 2 with an additional methylene group also affords compound 13 with a sequentially formed seven-membered and six-membered ring. The similar catalytic cyclization reaction of 2 by [Ru]NCCH3+ in the first stage is also demonstrated to give 8 in high yield. Likewise, the vinylidene complex 4 is acquired from 2 with [Ru]Cl. A series of phenyl propargyl alcohol 19, 20, 20’ and 21 having two methyl groups on the terminal carbon of the ortho tethering chain were synthesized. The catalytic cyclization reaction of 19 by [Ru]NCCH3+ directly afford the second stage product 23. The formation of the tricyclic product 23 proceeds in the same way as we mentioned above. In this catalytic cycle, many attempts to isolate the vinylidene intermediate O failed. A fast addition of terminal olefinic moiety to Cα of the vinylidene ligand followed by a demetalation process yields the final product. Without the methyl group, two similar phenyl propargyl alcohols 27 and 28, in the reactions with [Ru]Cl, yield no cyclization product. Only the phosphonium acetylide complex 29, 30, the allenylidene complex 31 or the methoxy carbene complex 32 are obtained. All cyclic vinylidene complexes and organic compounds are characterized by NMR spectra.
Three 1,6-enyne compounds 33-35 each containing pendant olefinic groups, which have zero, one or two methyl groups, are prepared. Reaction of enyne 33a with [Ru’]Cl ([Ru’] = Cp(dppe)Ru) in CH2Cl2 yields the allenylidene complex 38. In MeOH, the same reaction gives a mixture of the γ-methoxyvinylidene complex 36a and the α-methoxycarbene complex 37. Deprotonation of 36a generate the acetylide complex 39, however, treatment of 39 with HBF4 in MeOH is readily followed by a methoxide addition to generate 37. Astonishingly, with the presence of two hydrogens at the terminal olefinic carbon, complex 36a undergoes a cyclization in air to give the vinylidene complex 40a containing a spiral ring system and mixed phosphine oxide of dppe as a minor product. Complex 40a is characterized by 1H, 13C, 31P, 1H-1H COSY, 1H-13C HSQC and 1H-13C HMBC NMR spectroscopy. Analogous complex 40a’ is directly obtained from the reaction of [Ru]Cl ([Ru] = Cp(PPh3)2Ru) with enyne 33a in MeOH in air. Protonation of 40a causes formation of the 1,3-migration product 44 and 44’. Moreover, base induced reaction of complexes 44 and 44’ leads to the neutral acyl complex 45. Finally, the spiral organic compound 46 with an aldehyde group is obtained from the reaction of 45 with HCl. In addition, the reactions of 1,6-enyne 34 with [Ru]Cl and [Ru’]Cl both proceed via a 5-exo-dig cyclization pathway to give the carbene complexes 47 and 47’, respectively. For the enyne 35 with one methyl groups at the internal carbon of the olefinic part, formation of the carbene complexes 48 or 49 may then involve a 6-exo-dig cyclization to give the tertiary carbocation, ultimately leading to 48 in methanol and 49 in CH2Cl2.
Subjects
釕金屬
亞乙烯基錯合物
丙烯基錯合物
催化環化反應
三級碳陽離子
聯繼環化反應
氧誘發環化
環接化合物
Type
thesis
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