One-Pot Synthesis of Substituted Furans and Pyrroles from Propargylic Dithioacetals. New Annulation Route to Highly Photoluminescent Oligoaryls

Abstract

Oligoaryl is an important class of compounds which exhibit a variety of fascinating properties for optoelectronic interests. 1 Incorporation of five-membered heteroaromatic moieties into these conjugated molecules will occasionally increase fluorescence quantum yields and the optoelectronic properties of the oligomers can be tuned. 1 Most syntheses of these heteroaromatic containing oligomers involve the transition-metal catalyzed cross coupling reactions of the corresponding aryl components. 2 In general, the presence of a long chain aliphatic substituent in these heteroaromatic rings will increase the solubility in organic solvent and hence enhance the processibility of these materials. 1 However, introduction of such alkyl substituent at C 3 and/or C 4 positions in these heteroaromatic rings for further cross coupling reactions is not trivial. 3 Cyclization of the 1,4-dicarbonyl moiety with heteroatom-containing reagents provides an alternative procedure for the construction of these five-membered heterocycles. [3][4][5] It is known that annulation of allenylmethanols can afford the corresponding five-membered oxygen heterocycles. 6 In addition, annulation of allenyl carbonyl compounds, 7 propargylic acetals, 8 or oxiranes 9,10 furnishes a powerful arsenal for the synthesis of substituted furans. The applications of propargylic metallic species have paved a useful path for the construction of furan skeletons. 11 We recently reported that propargylic dithioacetal 1 can serve as an allene 1,3-zwitterion synthon (eq 1). 12 The interesting feature for this reaction involves an umpolung of one of the two carbonsulfur bonds in the dithioacetal functionality. The organocopper intermediate 2 can react with a number of electrophiles leading to either allenyl or alkynyl product 3 or 4. The chemoselectivity of this reaction depends on the nature of the electrophile. It is envisaged that the reaction of 2 with an aldehyde 6 or an aldimine 8 may yield the intermediate alcohol 5a, or amine 5b, respectively.

Heterophenes revisited

“…We began our research on oligoaryl-containing heterophanes by employing our new protocols for furan and pyrrole annulations [16][17][18][19][20][21]. Thus, when the propargylic dithioacetal 5 is treated with BuLi or organocuprate reagent, the nucleophile selectively attacks the sulfur atom of the propargylic dithioacetal, leading to the corresponding allenyl anion 6 or propargylic anion 7.…”

“…Thus, when the propargylic dithioacetal 5 is treated with BuLi or organocuprate reagent, the nucleophile selectively attacks the sulfur atom of the propargylic dithioacetal, leading to the corresponding allenyl anion 6 or propargylic anion 7. Reaction of 6 or 7 with an aldehyde 8 yields selectively the corresponding allenylcarbinol 9, which is cyclized upon treatment with trifluoroacetic acid (TFA) to give furan 10 (Scheme 1) [18]. This procedure provides a useful entry toward the synthesis of furan-containing teraryls (10, R 1 = R 3 = Ar) when appropriate substrates 5 and 8 are used.…”

“…Alternating benzene-furan oligoaryls are highly fluorescent with high quantum yield [18][19][20]22,23]. It is known that furan compounds are light-sensitive and can easily be oxidized by singlet oxygen.…”

The Application of Iron (Iii) Phosphate in the Synthesis of N-Substituted Pyrroles

“…Consequently, many methods for the synthesis of diversely substituted pyrroles have been developed such as montmorillonite, KSF 12 , microwave irradiation 13,14 , Bi(NO 3 ) 3 .5H 2 O 15 , Sc(OTf) 3 16 , TolSO 3 H 17 , layered zirconium phosphate and zirconium sulfophenyl phosphonate 18 , titanium 19 or TiCl 4 /Et 3 N 20 . Some of other methods for synthesis of pyrroles include: conjugate addition reactions 21 , annulation reactions 22,23 , multicomponent reactions 24,25 and aza-Wittig reactions 26 . However, several of these methods require prolonged reaction times, use of volatile organic solvents and toxic metals.…”

Reaction of acetophenone and benzylphenylketone oximes with phenylacetylene: synthesis of di- and triphenylpyrroles

“…2а, 3 A series of 2,3,4-triphenylpyrrole derivatives exert high hypoglycemic action and can be recommended for diabetes treatment. 2а Although arylpyrroles are applied for the synthesis of fluorescent azaindacene dyes of BODIPY family 4 as well as optoelectronic materials, 5 it is their pharmacological appeal that seems to be the chief reason for a steady interest in the development of synthetic procedures for these compounds, reported, in particular, in reviews. 1,2 Di-and triphenylpyrroles are normally prepared by condensation of 1,4-diketones with ammonia or ammonium acetate, [6][7][8][9] as well as by the reaction of 1,3-diketones 10,11 with different nitrogen-containing compounds (ammonium acetate, aromatic imines, oximes) followed by cyclization of the intermediates formed.…”