Sequential Insertion of Alkynes, Alkenes, and CO into the Pd–C Bond of ortho-Palladated Primary Phenethylamines: from η³-Allyl Complexes and Enlarged Palladacycles to Functionalized Arylalkylamines

Abstract

The eight-membered metallacycles arising from the insertion of 1 equiv of alkyne into the Pd–C bond of ortho -metalated homoveratrylamine and phentermine can further react with alkenes to give two different types of mononuclear complexes depending on the nature of the olefin. When terminal alkenes (styrene and ethyl acrylate) are used, a mixture of the anti / syn η 3 -allyl Pd(II) complexes are isolated, which evolve slowly to the syn isomers by heating the mixtures appropriately. These η 3 -allyl Pd(II) complexes do not react with CO or weak bases, but when they are treated with a strong base, such as KO t Bu, they afford Pd(0) and the functionalized starting phenethylamines containing a 1,3-butadienyl substituent in an ortho position. When 2-norbornene was used instead of terminal alkenes, the strained olefin inserts into the alkenyl Pd(II) complex to afford a 10-membered norbornyl palladium(II) complex, in which the new C , N -chelate ligand is coordinated to the metal through an additional double bond, occupying three coordination positions. The reactivity of these norbornyl complexes depends on the substituents on the inserted alkenyl fragment, and thus they can further react with (1) KO t Bu, to give Pd(0) and a tetrahydroisoquinoline nucleus containing a tricyclo[3.2.1]octyl ring, or (2) CO and TlOTf, to afford Pd(0) and amino acid derivatives or the corresponding lactones arising from an intramolecular Michael addition of the CO 2 H group to the α,β-unsaturated ester moiety. Crystal structures of every type of compound have been determined by X-ray diffraction studies.

Synthesis and Reactivity of Dipalladated Derivatives of Terephthalaldehyde

“…19−41 Organic substituents ortho to the Pd atom may be involved in this chemistry, yielding novel structures and potentially useful organic compounds. [21][22][23][24][25][26][27][28][29][30]34,35 We have been interested in exploring the extension of this chemistry to di- 42,43 and tripalladated 44−47 benzene derivatives orthosubstituted at each Pd(II) center. Thus, our group has reported the synthesis and reactivity of mono-, di-, and tripalladated derivatives of mesitylene, 44,46 benzenetricarboxaldehyde, 45 and tris(styryl)benzene 47 (Chart 1A), as well as dipalladated derivatives of 2,5-distyrylbenzene 42,43 (Chart 1B).…”

Synthesis of mono-, di- and tripalladated 1,3,5-benzenetristyryl complexes. CO insertion to give a dipalladated indenone

“…1–17 Consequently, there are many publications related to their synthesis, characterization, and reactivity. 18–36 In particular, the presence of organic substituents ortho to the Pd atom has been shown to provide a very rich and varied chemistry, because they frequently participate in the reactivity of these complexes, resulting in interesting new structures and the formation of novel and potentially useful organic compounds. 20–29,33,34,37,38 Some time ago, we started to explore the possibility of extending this chemistry to di- 25,26 and tripalladated 39–41 benzene derivatives, ortho -substituted at each Pd( ii ) centre.…”

“…[1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17] Consequently, there are many publications related to their synthesis, characterization, and reactivity. [18][19][20][21][22][23][24][25][26][27][28][29][30][31][32][33][34][35][36] In particular, the presence of organic substituents ortho to the Pd atom has been shown to provide a very rich and varied chemistry, because they frequently participate in the reactivity of these complexes, resulting in interesting new structures and the formation of novel and potentially useful organic compounds. [20][21][22][23][24][25][26][27][28][29]33,34,37,…”

“…[18][19][20][21][22][23][24][25][26][27][28][29][30][31][32][33][34][35][36] In particular, the presence of organic substituents ortho to the Pd atom has been shown to provide a very rich and varied chemistry, because they frequently participate in the reactivity of these complexes, resulting in interesting new structures and the formation of novel and potentially useful organic compounds. [20][21][22][23][24][25][26][27][28][29]33,34,37,38 Some time ago, we started to explore the possibility of extending this chemistry to di- 25,26 and tripalladated [39][40][41] benzene derivatives, ortho-substituted at each Pd(II) centre. Thus, in 2001 some of us reported the first tripalladated benzene derivative, resulting from the 3-fold oxi-dative addition of 1,3,5-triiodomesitylene to 3 equivalents of [Pd(dba) 2 ].…”

Synthesis of Benzofused O- and N-Heterocycles through Cascade Carbopalladation/Cross-Alkylation of Alkynes Involving the C–C Cleavage of Cyclobutanols

“…With these precedents in mind, and given our interest in the topics of Pd chemistry and the processes related to C–C cleavage, − we aimed to extend the applicability of these types of cascades to the synthesis of heterocycles bearing an alkylated olefine moiety (Scheme ).…”