1,2,3,4‐Tetrasubstituted Cyclopentadienes and Their Applications for Metallocenes: Efficient Synthesis through Zirconocene‐ and CuCl‐Mediated Intermolecular Coupling of Two Alkynes and One Diiodomethane

Abstract

1,2,3,4-Tetrasubstituted cyclopentadienes and indene derivatives with identical or different substituents were obtained in good to excellent isolated yields through a zirconocene- and CuCl-mediated intermolecular coupling process. This synthetic procedure involved three organic partners, including one CH2 I2 , and two different or identical alkynes. Two alkynes or one diyne undergo Cp2Zr(II)-mediated (Cp = η(5)-C5H5) pair-selective reductive coupling to afford the corresponding zirconacyclopentadiene derivatives, which react, in the presence of CuCl and 1,3-dimethyl-3,4,5,6-tetrahydro-2(1 H)-pyrimidinone (DMPU), with CH2I2 through intermolecular followed by intramolecular coupling to afford the cyclopentadiene derivatives. An application of the prepared tetrasubstituted cyclopentadiene derivatives was demonstrated by the facile synthesis of the corresponding zirconocene complexes [((4R)Cp)2ZrCl2] and [((4R)Cp)2ZrR'2] (R' = Me, Et, or nBu). The unique 1,2,3,4-tetrasubstituted cyclopentadiene ligands and the corresponding metallocenes are expected to have further applications in organometallic chemistry and organic synthesis.

Synthetic Routes towards Multifunctional Cyclopentadienes

“…Ensuing intermolecular coupling with CH 2 I 2 and final intramolecular coupling afforded the described Cps. (Scheme B) . In all the above procedures, the Cps are obtained in good yields and no isomer formation is reported.…”

“…(Scheme 2B). [9] In all the above procedures, the Cps are obtained in good yields and no isomer formationi sr eported. The scope of substituents that can tolerate the reactionc onditions seems to be the limiting factor in this approach.…”

Nickel‐catalyzed three‐component coupling reaction of terminal alkynes, dihalomethane and amines to propargylamines

“…Later Cu(I), nano‐In 2 O 3 , Fe(III) and cobalt were also proved to catalyze this kind of AHA coupling reaction. Xi and co‐workers have reported the use dihalomethane as a carbon source, as well as a geminal dihalide to also act as a carbon source . Unfortunately, the requirement for specially designed nano‐sized catalysts and the use of precious transition metals such as Au or In are some of the drawbacks of this protocol.…”

Double CF Bond Activation through β‐Fluorine Elimination: Nickel‐Mediated [3+2] Cycloaddition of 2‐Trifluoromethyl‐1‐alkenes with Alkynes

“…This methodology simultaneously enables the direct construction of a multisubstituted cyclopentadiene ring and the introduction of a fluorine substituent or a trifluoromethyl group in a regioselective manner. [16] Fluorine-containing, multisubstituted cyclopentadienes would be useful compounds as ligands of metallocene-type complexes [17] and as building blocks for further chemical transformations such as Diels-Alder reactions. [18,19] …”