Synthetic Applications of 3,4-Bis(trimethylsilyl)thiophene:  Unsymmetrically 3,4-Disubstituted Thiophenes and 3,4-Didehydrothiophene^,

Abstract

3,4-Bis(trimethylsilyl)thiophene (1a) was synthesized by three routes: (a) 1,3-dipolar cycloaddition; (b) modification of 3,4-dibromothiophene; and (c) intermolecular thiazole-alkyne Diels-Alder reaction. 3,4-Bis(trimethylsilyl)thiophene (1a) can function as a versatile building block for the construction of unsymmetrically 3,4-disubstituted thiophenes utilizing its stepwise regiospecific mono-ipso-substitution followed by palladium-catalyzed cross-coupling reactions. In this manner, thiophenes 15, 16, 17a-j, 19a,b, 20, 22a-c, 23a,b, 24a-d, 25a-c, and 27a-j were prepared. The thiophene-3,4-diyl dimer 28 and thiophene-3,4-diyl tetramer 29 were also realized by palladium-catalyzed self-coupling reaction of organoboroxines. The stannylthiophene 31, formed by conversion of the C-Si bond to a C-Sn bond via boroxine 26c underwent both carbonylative coupling and lithiation followed by quenching with electrophiles to afford unsymmetrically 3,4-disubstituted thiophenes 33 and 36a-c as well. Moreover, 3,4-bis(trimethylsilyl)thiophene (1a) can be used as the starting material for the generation of the highly strained cyclic cumulene 3,4-didehydrothiophene (2), whose existence was substantiated by its trapping reaction with several alkenes.

Advances in Synthetic Applications of Hypervalent Iodine Compounds

“…The heteroaromatic analogues of 445 , phenyl­[4-(trimethylsilyl)­thien-3-yl]­iodonium triflate 448 , , and phenyl [1- tert -butoxycarbonyl-4-(trimethylsilyl)-1 H -pyrrole-3-yl]­iodonium triflate 450 , have been prepared from the appropriate heteroaromatic bis­(trimethylsilyl) compounds and (diacetoxyiodo)­benzene in the presence of triflic acid. The respective benzyne analogues can be generated from 448 or 450 by the treatment with potassium fluoride and trapped by the reaction with furan 446 at room temperature to give the corresponding adducts 449 and 451 (Scheme ).…”

Iodonium Salts as Benzyne Precursors

“…[38,39,41,[80][81][82] The startingm aterials, 1,2-bis(trimethylsilyl)arenes 43 are commerciallya vailable or can be obtained by disilylationr eactions of 1,2-dichlorobenzenes in moderate yields. [83] Several other aryne precursors such as (phenyl)[3-trimethylsiyl)-2-naphthyl]-iodonium triflate 45, [84] phenyl[4-(trimethylsilyl)thien-3-yl]iodonium triflate 46, [85,86] and [1-tert-butoxycarbonyl-4-(trimethylsilyl)-1 H-pyrrole-3-yl]iodonium triflate 47 [87] have been prepared similarly from the corresponding bis(trimethylsilyl) compounds and (diacetoxyiodo)benzene in the presence of TfOH (Scheme 14). Solid state structure of [1tert-butoxycarbonyl-4-(trimethylsilyl)-1 H-pyrrole-3-yl]iodonium triflate 47 wasconfirmed by X-ray crystallography.…”

“…[84] This result was superior to the reaction of 2-naphthyl-aryliodonium-3-carboxylate with 59 under heating conditions. [64] Heteroaromatic analogueso fr eagent 48,p henyl[4-(trimethylsilyl)thien-3-yl]iodonium triflate 46, [85,86] and [1-tert-butoxycarbonyl-4-(trimethylsilyl)-1 H-pyrrole-3-yl]iodonium triflate 47, [87] have been developed. Reagents 46 and 47 can react, for example, with furan in the presence of fluoride source to form the corresponding products of cycloadditioni nl ow to moderate yields.…”

“…Heteroaromatic analogues of reagent 48 , phenyl[4‐(trimethylsilyl)thien‐3‐yl]iodonium triflate 46 , and [1‐ tert ‐butoxycarbonyl‐4‐(trimethylsilyl)‐1 H ‐pyrrole‐3‐yl]iodonium triflate 47 , have been developed. Reagents 46 and 47 can react, for example, with furan in the presence of fluoride source to form the corresponding products of cycloaddition in low to moderate yields.…”

Carbanion generation through tin-lithium exchange of vinyl-, aryl-, and hetarylstannanes

“…Tin-lithium exchange has also been reported to occur in a 3-tributylstannylthiophene under the same conditions (Equation 47). 76 Reaction of the generated organolithium compound with electrophiles such as acetone, DMF, or PhSeBr gave the expected products in moderate yields. Transmetallation of bis(stannyl) derivatives has also been reported.…”