Sonogashira reaction thiophenes

Sonogashira reactions of both a-halothiophenes [117] and P-halothiophenes [118] proceed smoothly even for fairly complicated molecules as illustrated by the transformation of brotizolam (134) to alkyne 135 [119]. Interestingly, 3,4-bis(trimethylsilyl)thiophene (137), derived from the intermolecular cyclization of 4-phenylthiazole (136) and bis(trimethylsilyl)acetylene, underwent consecutive iodination and Sonogashira reaction to make 3,4-bisalkynylthiophenes [120], Therefore, a regiospecific mono-i/wo-iodination of 137 gave iodothiophene 138, which was coupled with phenylacetylene to afford alkynylthiophene 139. A second iodination and a Sonogashira reaction then provided the unsymmetrically substituted 3,4-bisalkynylthiophene 140. 

DTF, 3,6-DSF as well as 2,7-DTF and 2,7-DSF from 3,6-dibromo-9,9-dioctylfluorene in which the key step, shown below, is the regioselec-tive Sonogashira reaction followed by a thiolate/selenoate cyclization reaction which results in the synthesis of regio-specific thiophene-based... 

Some drawbacks of the precursor routes mentioned above have been overcome by the use of polycondensation- and C-C-bond-coupling reactions. To produce soluble PPV-, poly(thiophene)-, or poly(pyrrol) derivatives for spin coating preparation, various types of transition metal catalyzed reactions, such as the Heck-, Suzuki-, and Sonogashira-reaction, Wittig- and Wittig-Horner-type coupling reactions, or the McMurry- and Knoevenagel-condensation have been utilized. 

The Sonogashira reaction with TMSA could also be succes-fully accomplished in the coupling with different heteroaryles such as pyrroles, thiophenes, pyrimidines, purines, and quinazolines. ... 

The indole compound was described by Flynn et al. [73] and is prepared in a similar manner as the thiophene 103 and furan 108. One method involved a similar synthesis as described in Scheme 25, using the relevant starting material. However, an alternative synthesis involved a one-pot, room-temperature synthesis, Scheme 27. The o-iodotrifluoroacetanilide 110 was coupled to the alkyne 111 under Sonogashira conditions in MeCN. K2CO3 and the aryliodo compound 107 was added and the reaction stirred to produce the protected product 112 with a 77% yield. Deprotection to the corresponding phenol 113 was performed using AICI3. 

A novel catalytic reaction of 3-iodothiophene-2-carboxylic acid with terminal alkynes leading to 4-alkynylthieno[2,3- ]-pyran-7-ones has been described <2006TL83>. This extension of the Sonogashira coupling occurs under Pd-Cu-catalysis (Equation 28). The reaction seems to proceed through an initial Sonogashira pathway to 3-( 1 -alkynyl)thiophene-2-carboxylic acid, which then reacts with a Pd(ll) species formed by insertion of a Pd(0) complex into the C-H bond of the second molecule of alkyne. Both Pd- and Cu-catalysts played cmcial roles, since the reaction failed if either was omitted. 

As with thiophene, 2,3-dibromobenzo[/ ]thiophene also exhibits a high regioselectivity in coupling reactions <2005T2245>. For example, Sonogashira coupling with /-butylacetylene leads exclusively to the 3-bromo derivative 90. 2,3-Unsymmetrically substituted derivatives of benzo[/ ]thiophene can be obtained by two successive crosscoupling reactions (Scheme 18). 

Acylation, vinylation, and ethinylation involving Pd(0)-catalyzed coupling reactions can be performed with halothiophenes, thiophene boronic acids, or thienyl stannanes following the classical Suzuki-Miyaura, Stille, or Sonogashira protocols [64]. 

The preparation of (alk-l-ynyl)thiophenes 154 is possible via palladium-catalyzed Sonogashira cross-coupling reactions between iodo- or bromothiophenes 152 and terminal alkynes 153 (Scheme 60, Table 38) [309, 360, 363, 364], Alkynylated thiophenes represent an important structural motif found in many ir-electronic systems such as molecular rods or conjugated macrocycles [163, 362, 365, 366], In the case of bromoiodo-substituted thiophenes, the more reactive iodine atom is replaced selectively [367]. Some coupling methods require stoichiometric amotmts of paUadium(0) [360, 368], whereas other methods proceed successfully tmder photochemical conditions without the need of a catalyst [369]. Recent... 

The reaction of 2,6-dioclyl-4,8-diethynyl-benzo[l,2-b 4,5-b ]dithiophene with dibromide compounds in toluene by Pd/Cu-catalyzed Sonogashira coupling copolymerization produced the polymers PEBBDT and PEBTTZ. Thiophene-3-carboxylic acid was similarity converted into the 2,6-Dioctyl-4,8-diethynyl-benzo [l,2-b 4,5-b ]dithiophene as the synthesis of common BDT compound [72]. EoUowing a three-component reaction, aldehyde, sulfur, and cyanoacetate of the 2-aIkyl substituted thiophene unit was converted into 2-amino thiophene [73]. The compound was obtained in good yield by the reaction of deamination and hydrolysis. PEBBDT was readily soluble in organic solvents like chloroform, THE, chlorobenzene (CB), etc. at room temperature but PEBTTZ was less soluble in these solvents [71]. 

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