166825-50-9Relevant articles and documents
Formation of Seven-Membered Carbocycles via 7-endo Mode Cyclization of Lithioheptatrienes
Kanno, Ken-ichiro,Igarashi, Eri,Mizukami, Yuki,Nakajima, Kiyohiko,Song, Zhiyi,Takahashi, Tamotsu
supporting information, p. 6217 - 6219 (2016/12/23)
The highly selective synthesis of triene derivatives was achieved by a zirconocene-mediated three-component coupling reaction, and the trienes were efficiently subjected to 7-endo mode cyclization. The reaction of unsymmetrical zirconacyclopentadienes prepared from two different alkynes with N-bromosuccinimide (NBS) followed by treatment with allyl halides in the presence of CuCl afforded the corresponding heptatrienes in good yields. When the trienes reacted with an organolithium reagent, 7-endo mode cyclization occurred smoothly to give the corresponding cycloheptadiene.
Multiple mechanistic pathways for zirconium-catalyzed carboalumination of alkynes. Requirements for cyclic carbometalation processes involving C-H activation
Negishi, Ei-Ichi,Kondakov, Denis Y.,Choueiry, Danièle,Kasai, Kayoko,Takahashi, Tamotsu
, p. 9577 - 9588 (2007/10/03)
The reactions of internal and terminal alkynes with organoalanes containing Et, n-Pr, and i-Bu groups in the presence of Cp2ZrCl2 and MeZrCp2Cl were investigated with the goal of clarifying mechanistic details of some representative cases. Three fundamentally different processes, i.e., (i) C-M bond addition without C-H activation in the alkyl group, (ii) cyclic C-M bond addition via C-H activation, and (iii) hydrometalation, have been observed, and the courses of these reactions significantly depend on (i) the nature and number of alkyl groups in organoalanes, (ii) their amounts, and (iii) solvents. The reaction of alkynes with Et3Al in the presence of 0.1 equiv of Cp2ZrCl2 in nonpolar solvents, e.g., hexanes, proceeds via C-H activation to give the corresponding aluminacyclopentenes. Investigation of the reaction of 5-decyne with 1-3 equiv of Et3Al and 1 equiv of Cp2ZrCl2, which gave mono-, di-, or trideuterated (Z)-5-ethyl-5-decene as shown, together with the previously reported structural study on the reaction of Et3Al with Cp2ZrCl2 leading to the formation of well-characterized bimetallic species 9, 10, and 11, supports a catalytic cycle involving bimetallic species 10 and 18. In summary, this process requires a zirconocene derivative containing one Zr-bound Et group which is linked to Et3Al (but not to Et2AlCl) through a Cl bridge, i.e., 18, to produce 10 via β C-H activation. In sharp contrast, the reaction of Et2AlCl-Cp2ZrCl2 as well as of (n-Pr)2AlCl-Cp2ZrCl2 does not involve any C-H activation processes. It proceeds well in chlorinated hydrocarbon solvents, e.g., (CH2Cl)2, but it is extremely sluggish in nonpolar solvents, e.g., hexanes. The reaction may well involve direct C-Al bond addition to alkynes, as suggested earlier for Zr-catalyzed Me-Al bond addition to alkynes, but a few other alternatives cannot be ruled out on the basis of the currently available data. The reaction of alkynes with (n-Pr)3Al-Cp2ZrCl2 in nonpolar solvents proceeds partially via C-H activation and partially via hydrometalation. In contrast with the C-H activation process observed with Et3Al, that with (n-Pr)3Al is totally dominated by dimerization of alkynes to give aluminacyclopentadienes rather than aluminacyclopentenes, reflecting a previously established generalization that propene can be much more readily displaced from Zr by alkynes than ethylene. Hydrometalation is the exclusive process with (i-Bu)3Al-Cp2ZrCl2. This hydrometalation reaction, however, reveals a few interesting complications. Alkyl-substituted internal alkynes give double bond migrated products in addition to the expected hydrometalation products. With terminal alkynes the reaction produces the expected hydrometalation products and the 1,1-dimetalloalkanes in comparable yields. Various other related reactions involving other alkynes, e.g., PhC≡CPh, n-OctC≡CH, and PhC≡CH, and other reagents, e.g., Et3Al-MeZrCp2Cl, Et2AlCl-MeZrCp2Cl, and (n-Pr)3Al-MeZrCp2Cl, were also studied.
