I Exchange

Letter pubs.acs.org/OrgLett

Construction of Functionalized Annulated Sulfone via SO2/I Exchange of Cyclic Diaryliodonium Salts Ming Wang,† Shihao Chen,† and Xuefeng Jiang*,†,‡ †

Shanghai Key Laboratory of Green Chemistry and Chemical Process, School of Chemistry and Molecular Engineering, East China Normal University, Shanghai 200062, P.R. China ‡ State Key Laboratory of Organometallic Chemistry, Shanghai Institute of Organic Chemistry, Chinese Academy of Sciences, Shanghai 200032, P.R. China S Supporting Information *

ABSTRACT: A straightforward protocol for diarylannulated sulfone construction is efficiently established via SO2/I exchange of iodonium(III) salts. Readily available inorganic Na2S2O5 was served as a safe and convenient SO2 surrogate. Diverse functionalized diarylannulated sulfones were smoothly achieved in good to excellent yields with great functional group compatibility. Organic light emitting diodes (OLEDs) material molecules were subsequently established via this method in gram scale. The unsymmetrical conjugated systems with donor-acceptor groups and πconjugation bridges motifs, which substantially communicate electron mobility in semiconductor material molecules, were successfully afforded under the facile conditions of the exchange strategy.

D

efficient diarylannulated sulfones construction through direct SO2/I exchange of diaryliodonium salts with inorganic sodium metabisulfite (Na2S2O5) as a SO2 surrogate. We commenced our study using the safe and commercially available Na2S2O5 as a SO2 source, avoiding dangerous gaseous SO2. Because Pd has exhibited great catalytic activation for SO2 coupling,6−9 diaryliodonium salt 2a and Na2S2O5 were first conducted in the presence of Pd(OAc)2 and PPh3, which disappointingly no desired dibenzannulated sulfone 3a was detected (Table 1, entry 1). Nevertheless, 3a was afforded in 14% yield when copper acetate and 1,10-phenanthroline was served as the catalyst (Table 1, entry 2), which is a rare example of SO2 releasing from a salt without strong acid. Copper(II) trifluoromethanesulfonate with the conjugated bidentate ligand 1,10-phenanthroline displayed a better result in 45% yield (Table 1, entries 3−5). TBAB, helping increase the solubility of salts, drastically promoted the yield to 71% (Table 1, entry 6). A stronger base Cs2CO3 inversely destroyed the transformation (Table 1, entry 7). Potassium phosphate as the base was the best choice, affording 3a in 82% yield (Table 1, entries 8−9). Other SO2 sources, such as K2S2O5, DABSO, and NaHSO3, furnished lower yields (Table 1, entries 10−12). With the optimized conditions in hand, comprehensive SO2/I exchange was shown in Scheme 1, which afforded a divergent functionalized diarylannulated sulfones library. Because the electrical characteristics are critical for adjusting a better charge balance in the material molecules,1d a broad range of conjugated diarylannulated sulfones substituted with electron-donating (for the capture of hole carriers) (3b−3d) and electron-withdrawing

iarylannulated sulfones play a significant role in organic photoconducting material chemistry for their unique performance of electronic and optical properties.1 As shown in Figure 1A, diversiform diarylannulated sulfones molecules are promising structures for organic light emitting diodes (OLEDs) material due to the extraordinary photophysical properties of diarylannulated sulfone in contrast with corresponding thioether.2 The presence of an S,S-dioxides motif tremendously lowers the energy of HOMO orbitals, enabling a requisite increase in electron affinities and solid-state photoluminescence (PL) efficiency.2c Conventionally, diarylannulated sulfones3 were achieved from oxidation of corresponding thioethers4 with strong oxidant after the coupling cyclization of problematic thiols (Figure 1B). Furthermore, the strategy of straightforward introduction of SO2 into organic frameworks is a challenge, which has gained great attention due to its atom economy, step economy, and recycling hazardous SO2.5 Great efforts have been contributed by the Willis and Wu groups toward the introduction of SO2 into aryl reagents and coupling partners, such as hydrazines,6 alkyl halides,7 aryl halides,8 and electrophilic fluorines,9 in which SO2 was employed as electrophile. Diaryliodonium salt, as a mature and readily available reagent, has been found to be one of the most efficient arylation reagents in organic synthesis.10 The direct insertion of SO2 into diaryliodonium salt will be highly efficient and pose a challenge because the low-lying LUMO orbital of SO25b sharply decreases the nucleophilicity of electron lone pair in a S atom and obstructs the formation of two C-S bonds in one step. Despite the electrophilic diaryliodonium salt not matching with the same electrophilic ability of SO2, we envisioned that the radical property of diaryliodonium(III) salt will drive SO2/I exchange for two C-SO2 bond formations (Figure 1C). Here we disclose an © 2017 American Chemical Society

Received: August 1, 2017 Published: September 6, 2017 4916

DOI: 10.1021/acs.orglett.7b02388 Org. Lett. 2017, 19, 4916−4919

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Figure 1. Unsymmetrical conjugated sulfone synthesis.

Table 1. Condition Optimizationa additive

“SO2”

yield (%)b

K2CO3 K2CO3 K2CO3 K2CO3 K2CO3 K2CO3 Cs2CO3 DIPEA K3PO4

TBAB TBAB TBAB TBAB

Na2S2O5 Na2S2O5 Na2S2O5 Na2S2O5 Na2S2O5 Na2S2O5 Na2S2O5 Na2S2O5 Na2S2O5

0 14 30 45 34 71 0 55 82

K3PO4 K3PO4 K3PO4

TBAB TBAB TBAB

K2S2O5 DABSOc NaHSO3

59 70 57

entry

catalyst, ligand

base

1 2 3 4 5 6 7 8 9

Pd(OAc)2, PPh3 Cu(OAc)2, 1,10-phen CuI, 1,10-phen Cu(OTf)2, 1,10-phen Cu(OTf)2, bipyridine Cu(OTf)2, 1,10-phen Cu(OTf)2, 1,10-phen Cu(OTf)2, 1,10-phen Cu(OTf)2, 1,10-phen Cu(OTf)2, 1,10-phen Cu(OTf)2, 1,10-phen Cu(OTf)2, 1,10-phen

10 11 12

molecular materials,1b was employed in the six-membered substrates. Diarylannulated sulfones were also furnished when copper(II) was replaced by dimethylethanediamine (DMEDA), which initiated a radical process reported by Shi.12 Six-membered diarylannulated sulfones bearing the electron-rich (4a), and -deficient (4b−4c) groups at position 2 were readily achieved. Diaryliodonium salts with two different substituents at positions 2 and 6/7 were all effectively tolerated regardless of electrondonating or -withdrawing (4d−4k). The scope was further demonstrated through the successful syntheses of fused ring and multifunctionalized diarylannulated sulfones (4l−4m). By replacing the gem-dimethyl with cyclopropyl group, the high tension cyclic products 4n and 4o were efficiently afforded in good yields. To reveal the unique versatility and applicability of the exchange protocol, the syntheses of functional semiconductor material molecules were conducted. A gram scale synthesis of the pivotal material molecule 3s with two easily modified bromides in the structure was smoothly afforded, which could achieve the diverse construction of OLED material molecules accordingly (Scheme 2.1).13 Dibenzothiophene-S,S-dioxide with the symmetrical functional groups were well investigated, however, the core with the unsymmetrical conjugated groups were arduous to reach through the known methods. The compatibility of demanding unsymmetrically substituted functional groups was systematically probed in this SO2/iodine exchange strategy (Scheme 2.2). The substituents at position 2 with a naphthalene group and position 7 with a π-conjugation bridge type dimethylfluorene group were well tolerated, affording the corresponding product 3u in favorable yield. The other π-conjugated functional groups, 9-anthracene (3v), 10-phenyl-9-anthracene (3w), benzothiophene (3x), and phenylacetylene (3y), which always display the excellent performances in organic material science,1,2 were also successfully accommodated even with different electrical properties. Radical trapping experiments were conducted with the assistance of 1,1-diphenylethylene under the standard conditions. 2-Diphenylvinyl-2′-iodo-biphenyl 5 was isolated in 13% yield, which provided the evidence of a aryl radical intermediate involved in this transformation (Scheme 3a). To further confirm the formation of electrophilic “SO2” precursor, morpholin-4amine (6) was tested in the exchange transformation, 2′-iodo-Nmorpholino-[1,1′-biphenyl]-2-sulfonamide 7 was observed in moderate yield even without the Cu(II) and ligand (Scheme 3b).

a Reaction conditions: 2a (0.1 mmol), Na2S2O5 (0.2 mmol), catalyst (0.01 mmol), ligand (0.012 mmol), base (0.2 mmol), additive (0.12 mmol), solvent (1 mL), 12 h. bIsolated yield of 3a. cDABSO is DABCO·(SO2)2.

(for the capture of electron carriers) (3e−3j) at position 3 were systematically furnished in good to excellent yields, whose structure was further confirmed via X-ray diffraction analysis of 3e.11 The substituents on positions 1 (3k), 2 (3l), and 4 (3m) with different electronic properties were also well tolerated. The conjugated phenyl groups (3n−3p) and fused rings (3q), which are beneficial for carrier mobility in semiconductor materials molecules, were proved to be entirely compatible. Diaryliodonium salts bearing the halogen moieties, which provide the chances for further derivatization by the metal catalyzed coupling reactions, were perfectly accommodated (3r). In particular, 3s (CAS: 83834-12-2), which is a key pivot for construction of organic electroluminescent materials molecules, performed well through this strategy. Heteoaryl sulfone, derived from the corresponding iodonium salt, was also afforded (3t). Following the success establishment of planar five-membered diarylannulated sulfones library, the six-membered diarylannulated sulfones, which are confirmed nonplanar structures by Xray diffraction analysis of 4n,11 were further studied to exhibit a more divergent synthesis for the potential OLEDs material molecules via the current methodology (see Supporting Information for conditions optimization). gem-Dimethyl, an important contributor for charge transporting amorphous 4917

DOI: 10.1021/acs.orglett.7b02388 Org. Lett. 2017, 19, 4916−4919

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a

Reaction conditions: 2 (0.1 mmol), Na2S2O5 (0.2 mmol), TBAB (0.12 mmol), DMSO (1 mL), 12 h, isolated yields, n = 0, Cu(OTf)2 (0.01 mmol), 1,10-Phen (0.012 mmol), K3PO4 (0.2 mmol), 120 °C, n = 1, DMEDA (0.01 mmol), DIPEA (0.2 mmol), 110 °C.

Scheme 2. Syntheses of Sulfone-Containing Unsymmetrical Organic Materials Molecules

Scheme 3. Mechanistic Study

Thus, a postulated reaction pathway was depicted in Scheme 3c. Radical intermediate 8 was generated via oxidation of Cu(I) species forming Cu(II), which has been proved in hypervalent iodine chemistry.10 Subsequently, Na2S2O5 was captured by radical intermediate 8 forming the syntonic SO2 radical anion intermediate 9, followed by oxidation to intermediate 10 with Cu(II) reduced to Cu(I) again. The oxidative addition of aryl iodine with Cu(I) provided Cu(III) aryl species 11 as the Ullman type intermediate, which underwent a intramolecular ligand 4918

DOI: 10.1021/acs.orglett.7b02388 Org. Lett. 2017, 19, 4916−4919

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exchange generating intermediate 12. Reductive elimination of 12 gave the desired product 3a and regenerated Cu(I) catalyst. In summary, a new synthetic pathway to access the diarylannulated sulfone molecules is developed through the SO2/iodine exchange of diaryliodonium salts. This effective transformation employs the radical property of diaryliodonium (III) salt driving the formation of SO2 radical anion to realize the exchange strategy. Conjugated diarylannulated sulfones were established through the reaction, employing inorganic Na2S2O5 as a SO2 surrogate. Furthermore, the new types of symmetrical OLED materials molecules were comprehensively established in gram scale even with sensitive functional groups. The structural novel π-conjugated molecules were successfully established bearing unsymmetrical functional groups, which give great potentials as OLED materials molecules. Further materials syntheses and the exploration of their properties are underway in our laboratory.

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ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.orglett.7b02388. Experimental; NMR, X-ray, and analytical data (PDF) Crystallographic data for 3e (CIF) Crystallographic data for 3u (CIF) Crystallographic data for 3x (CIF) Crystallographic data for 3y (CIF) Crystallographic data for 4n (CIF)

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. ORCID

Ming Wang: 0000-0003-0388-4473 Xuefeng Jiang: 0000-0002-1849-6572 Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS We acknowledge financial support from NSFC (21722202, 21672069, 21472050, 21502054 for M.W.), DFMEC (20130076110023), Fok Ying Tung Education Foundation (141011), Program for Shanghai Rising Star (15QA1401800), Professor of Special Appointment (Eastern Scholar) at Shanghai Institutions of Higher Learning, and National Program for Support of Top-Notch Young Professionals.

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REFERENCES

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DOI: 10.1021/acs.orglett.7b02388 Org. Lett. 2017, 19, 4916−4919