Reported here is the use of 1-haloacetylenes and 1-halopolyynes as synthons for the preparation of new palladium(II) end-capped polyynes. The 1-haloalkynes were obtained in a series of transformations from para-substituted bromoarenes that included Sonogashira coupling followed by halogenation and chain elongation via Cadiot–Chodkiewicz protocol. The key step for the synthesis of metal complexes was oxidative addition of 1-haloalkynes to Pd(PPh3)4, which allowed obtaining a series of metal compounds 1–5-C n X with carbon chains up to hexatriyne in 75–100% yield. All the compounds were characterized by NMR and HRMS or elemental analysis. The 13C spectra of the 1-haloalkynes showed interesting, although expected, shifts of the carbon chain atoms close to the halogen termini. X-ray crystal structures were obtained for three polyynestwo butadiynes (2-C4[Pd]Br and 3-C4[Pd]Br) and one hexatriyne (1-C6[Pd]Br)and the latter is the first reported X-ray crystal structure of palladium end-capped hexatriyne.
The first planar π‐extended azulene that retains aromaticity of odd‐membered rings was synthesized by [3+3] peri‐annulation of two naphthalene imides at both long‐edge sides of azulene. Using bromination and subsequent nucleophilic substitution by methoxide and morpholine, selective functionalization of the π‐extended azulene was achieved. Whilst these new azulenes can be regarded as isomers of terrylene bisimide they exhibit entirely different properties, which include very narrow optical and electrochemical gaps. DFT, TD‐DFT, as well as nucleus‐independent chemical shift calculations were applied to explain the structural and functional properties of these new π scaffolds. Furthermore, X‐ray crystallography confirmed the planarity of the reported π‐scaffolds and aromaticity of their azulene moiety.
The synthesis of a unique series of long, asymmetric 1-iodopolyynes (1-Cn I and 2-Cn I) with the sp-hybridized carbon chain up to a decapentayne is reported. These compounds were then used as substrates in reactions with Pd(PPh3 )4 leading to another series of palladium end-capped polyynes, which were unstable in solution. Organometallic octatetraynes 1-C8 [Pd]I, 2-C8 [Pd]I, and decapentayne 1-C10 [Pd]I are palladium end-capped polyyne compounds with the longest carbon chains reported so far. All the complexes as well as their organic precursors were fully characterized by NMR, HRMS(ESI), IR, TGA-DTA, and UV/Vis techniques, and the X-ray crystal structures of two silyl-protected precursors and one palladium complex are presented. The synthetic approach for palladium species is envisioned as a general route for the synthesis of labile organometallic polyynes.
The work describes a convenient and highly efficient C-H butadiynylation of substituted pyrroles with the use of 1halobutadiynes. The method requires only a simple grinding of substrates in a mortar under mild, solvent-and transition metal-free conditions and constitutes the first example of pyrrole butadiynylation via cross-coupling reaction with the use of 1-halobutadiynes. The scope of this mechanochemical approach covers 4,5,6,7-tetrahydro-1H-indole, its N-substituted derivatives and 2-phenylpyrrole and on the other hand ester and phenyl end-capped 1-halobutadiynes including chlorides, bromides and iodides. Interestingly, the method has proven effective also for weak electron withdrawing aryl substituted 1-halobutadiynes what has not been yet achieved for 1-haloacetylenes. Such reactivity was unexpected in the view of the literature data and opened a gate to the plethora of substrates for organic synthesis including syntheses of pharmaceuticals. An X-ray analysis of two coupling products is also presented.A butadiyne (1 equivalent) was dissolved in acetonitrile (20 mL) in a Schlenk flask under N 2 atmosphere. Next H 2 O (2 eqivalents), N-halosuccinimide (1.2 equivalents) and AgNO 3 (0.3 equivalents)/KF(1.0 equivalent) or AgF (1.0 equivalent) were added. Flask was wrapped in aluminum foil and the reaction mixture was stirred for 3-24 h. Next the solvent was removed under reduced pressure and the product was purified by passing through short silica gel plug (hexanes/DCM, 1/2, v/v) yielding pure 1-halobutadiyne. Ethyl 5-chloropenta-2,4-diynoate (2b-Cl) Yellow oil (51 mg, 0.33 mmol), yield: 20%. 1 H NMR (500 MHz, CDCl 3 ): δ H 4.25 (q, J = 7.1 Hz, 2H), 1.31 (t, J = 7.1 Hz, 3H). 13 C NMR (126 MHz, CDCl 3 ): δ C 152.6, 70.4, 64.8, 64.5, 62.8, 54.0, 14.1. HRMS(ESI): m/z calcd for 157.0051; C 7 H 6 ClO 2 : [M+H + ]; found: 157.0051. Methyl 5-bromopenta-2,4-diynoate (2a-Br) Yellow crystals, yield: 71 mg (0.28 mmol), 56%; mp 69.2 -71.5 o C. 1 H NMR (CDCl 3 , 500 MHz): δ H 6.86 (dd, J = 16.0, 9.3 Hz, 1H), 6.57 (s, 1H), 5.38 (dd, J = 16.0, 1.2 Hz, 1H), 4.94 (dd, J = 9.3, 1.2 Hz, 1H), 3.80 (s, 3H), 2.64-2.62 (m, 2H), 2.48-2.45
A highly efficient one-pot procedure for the preparation of 1-chloroalkynes and 1-chlorobutadiynes from terminal and trialkylsilyl-protected precursors is reported. This convenient reaction, proceeding under mild conditions, utilizes N-chlorosuccinimide as the chlorinating agent and tolerates a range of functional groups.
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