Metal-promoted cyclization. 19. Novel bicyclization of enynes and diynes promoted by zirconocene derivatives and conversion of zirconabicycles into bicyclic enones via carbonylation

Abstract

Enynes and diynes react with "ZrCp," (where Cp = 7'-CSHs) generated by treating C12ZrCp, with Mg and HgCl, or 2 equiv of an alkyllithium, such as n-BuLi, or a Grignard reagent, such as EtMgBr, and can produce in excellent yields zirconabicycles represented by 2 (M = Zr) and 8, respectively. Their protonolysis can provide the corresponding exocyclic alkenes and conjugated dienes 9, respectively. Iodinolysis of 2 (M = Zr) can give the corresponding diiodides in high yields, while carbonylation of 2 (M = Zr) can produce bicyclic enones 3 (Y = 0) in moderate to good yields. Although the bicyclization reaction fails with terminal alkyne containing substrates, various types of substituents on the alkyne moiety, such as alkyl, alkenyl, aryl, trialkylsilyl, and trialkylstannyl groups, can be accommodated. Investigation of the n-BuLi-C12ZrCp, reaction has revealed that it gives first (~-B U )~Z~C~, at -78 "C, which then decomposes to give Cp,Zr(CH,=CHEt), identified as its PMe3 complex 11. The PMe3-stabilized complex reacts with diphenylacetylene to produce a crystalline compound which has been identified as a zirconacyclopropene, 36a. This demonstrated, for the first time, the feasibility of converting alkynes into zirconacyclopropenes. The reaction of preformed, three-membered zirconacycles with alkynes gives five-membered zirconacycles. The reaction of diphenylacetylene is ca. 150 times as fast as that of (@stilbene. These results support a mechanism involving formation of a zirconacyclopropene intermediate followed by its intramolecular carbometalation with the alkene moiety of enynes for the Zr-promoted bicyclization of enynes.Direct conversion of enynes into the corresponding metallabicycles followed by their conversion into bicyclic or even monocyclic organic compounds is, in principle, a synthetically attractive methodology2 (eq 1). Consideration of molecular orbital /=-z 3 \= R 1 4 R=C and heteroatom-containing chain. X=H. halogen,etc , Y = O , e t c , Z = H . C , S i , G e , o r Sn ( 1 )interactions suggested to us that it would be desirable to generate a 14-electron species with a t least one filled nonbonding orbital (5) or its equivalent containing a transition metal for facile conversion of 1 into 2 via a concerted process. Interaction of 1 with 5 can, in principle, lead to the formation of 6 or 7 through the use of a pair of orbitals: a filled nonbonding orbital ( H O M O ) and an empty orbital ( L U M O ) . Intramolecular carbometalation involving the second empty orbital should lead to the formation of 2 (eq 2). Indeed, "ZrCp," equivalents, where C p = $-C5H5, generated by two-electron reduction of Cp,Zr(IV) derivatives were (1) Metal-Promoted Cyclization. 19. Part 18: Negishi, E.; Boardman, L. D.; Sawada, H.; Bagheri, V.; Tour, J. M.; Rand, C. L. J. Am. Chem. SOC. 1988, 110, 5383. Some preliminary results of the work have been communicated: (a) Neghish, E.; Holmes, S. J.; Tour, J. M.; Miller, J. A. A cobalt-promoted methodology for converting 1 into 3 was known at the outset of our investigation. (a) Kha...

Selective Dimerization of Aryl-substituted Terminal Alkynes on Bis(indenyl)zirconocene Derivatives

“…There was no related product from the ¢,¢-diaryl isomer. Recently, Szymoniak reported similar result in a [Cp 2 ZrCl 2 ]/Ln system. 4 A mixture of 1,4-and 1,3-diphenylbutadiene in a ratio of 2.5 to 1 was obtained.…”

“…Zirconium indenyl complex, [(Ind) 3 ZrH] (9) was prepared by the reaction of [(Ind) 2 ZrBu 2 ] and an excess of indene as shown in eq 3.…”

“…Therefore 5a5e were selectively formed. It is important to note that [(Ind) 2 This paper is in celebration of the 2010 Nobel Prize awarded to Professors Richard F. Heck, Akira Suzuki, and Ei-ichi Negishi. Figure 2.…”

Cyclobutene photochemistry. Adiabatic photochemical ring opening of alkylcyclobutenes

“…1,7-Octadiyne, 1,6-heptadiyne (Wiley Organics), and 1,5-hexadiyne (Lancaster) were purified by alumina column chromatography using hexanes as the eluant. 2,6-Octadiyne, 2,7-nonadiyne, 2,8-decadiyne, and 2,9-undecadiyne were prepared according to the procedure of Negishi et al (30), and purified by alumina column chromatography (hexanes eluant). Oxalic acid (BDH Reagent) was recrystallized three times from water.…”

“…MS, m/z (1): 122 (20); 107 (23); 93 (60); 91 (64); 79 (100); 77 (53); 65 (17); 51 (15); 39 (27); 27 (17 (18); 39 (30).…”