Aryl(Mes)iodonium salts, which are multifaceted aryl transfer reagents, are synthesized via boron-iodane exchange. Modification to both the nucleophilic (aryl boron) and electrophilic (mesityl–λ 3 –iodane) reaction components results in improved yield and faster reaction time compared to previous conditions. Mechanistic studies reveal a pathway that is more like transmetallation than S E Ar.
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Regioselective Synthesis of 1,2,3,4‐Tetrasubstituted Arenes by Vicinal Functionalization of Arynes Derived from Aryl(Mes)iodonium Salts**
Herein, the synthesis of 1,2,3,4‐tetrasubstituted benzenoid rings, motifs found in pharmaceutical, agrochemical, and natural products, is described.[1]In the past, the regioselective syntheses of such compounds have been a significant challenge. This work reports a method using substituted arynes derived from aryl(Mes)iodonium salts to access a range of densely functionalized 1,2,3,4‐tetrasubstituted benzenoid rings. Significantly, it was found that halide substituents are compatible under these conditions, enabling post‐synthetic elaboration via palladium‐catalyzed coupling. This concise strategy is predicated on two regioselective events: 1)
- Award ID(s):
- 1828573
- NSF-PAR ID:
- 10233440
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Chemistry – A European Journal
- Volume:
- 27
- Issue:
- 24
- ISSN:
- 0947-6539
- Page Range / eLocation ID:
- p. 7168-7175
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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1,3-Dimethyl-2,3-dihydrobenzo[
d ]imidazoles,1H , and 1,1',3,3'-tetramethyl-2,2',3,3'-tetrahydro-2,2'-bibenzo[d ]imidazoles,1 2 , are of interest as n-dopants for organic electron-transport materials. Salts of 2-(4-(dimethylamino)phenyl)-4,7-dimethoxy-, 2-cyclohexyl-4,7-dimethoxy-, and 2-(5-(dimethylamino)thiophen-2-yl)benzo[d ]imidazolium (1g–i + , respectively) have been synthesized and reduced with NaBH4to1gH ,1hH , and1iH , and with Na:Hg to1g 2 and1h 2 . Their electrochemistry and reactivity were compared to those derived from 2-(4-(dimethylamino)phenyl)- (1b + ) and 2-cyclohexylbenzo[d ]imidazolium (1e + ) salts.E (1 + /1 • ) values for 2-aryl species are less reducing than for 2-alkyl analogues, i.e., the radicals are stabilized more by aryl groups than the cations, while 4,7-dimethoxy substitution leads to more reducingE (1 + /1 • ) values, as well as cathodic shifts inE (1 2 •+ /1 2 ) andE (1H •+ /1H ) values. Both the use of 3,4-dimethoxy and 2-aryl substituents accelerates the reaction of the1H species with PC61BM. Because 2-aryl groups stabilize radicals,1b 2 and1g 2 exhibit weaker bonds than1e 2 and1h 2 and thus react with 6,13-bis(triisopropylsilylethynyl)pentacene (VII ) via a “cleavage-first” pathway, while1e 2 and1h 2 react only via “electron-transfer-first”.1h 2 exhibits the most cathodicE (1 2 •+ /1 2 ) value of the dimers considered here and, therefore, reacts more rapidly than any of the other dimers withVII via “electron-transfer-first”. Crystal structures show rather long central C–C bonds for1b 2 (1.5899(11) and 1.6194(8) Å) and1h 2 (1.6299(13) Å). -
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Abstract Highly congested derivatives of biphenyl were prepared by double Diels‐Alder reactions of cyclopentadienones with substituted butadiynes. The reaction of 2,3,5‐tri(
tert ‐butyl)cyclopentadienone (5 ) and diphenylbutadiyne (3 ) gave only the single adduct, 1‐(phenylethynyl)‐2‐phenyl‐3,5,6‐tri‐tert ‐butylbenzene (6 ), and even extreme conditions gave no second addition. When tetracyclone (4 ) was added to bis(trimethylsilyl)butadiyne (8 ), two additions were achieved, but one silyl group was lost either during, or immediately following, the second addition to give 2‐(trimethylsilyl)‐2′,3,3′,4,4′,5,5′,6‐octaphenylbiphenyl (11 ). However, when 3,4‐diphenyl‐2,5‐dimethylcyclopentadienone (12 ) was added to8 , the fully substituted 2,2′‐bis(trimethylsilyl)‐4,4′,5,5′‐tetraphenyl‐3,3′,6,6′‐tetramethylbiphenyl (14 ) was formed. The X‐ray structures of compounds11 and14 show them to be quite crowded, but the central biphenyl rings do not exhibit the distortions previously observed in decaphenylbiphenyl. In an alternative approach, arynes were added to 5,5′‐bis(4‐chlorophenyl)‐3,3′,4,4′‐tetraphenyl‐2,2′‐bis(cyclopentadienone) (18 ). Simple benzyne added twice to give 4,4′‐bis(4‐chlorophenyl)‐2,2′,3,3′‐tetraphenyl‐1,1′‐binaphthyl (19 ) in low yield, but tetraphenylbenzyne, generated from tetraphenylanthranilic acid, added only once. -
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Abstract The first highly enantioselective, diastereoselective, and regioselective [2,3]‐rearrangement of iodonium ylides has been developed as a general solution to catalytic onium ylide rearrangements. In the presence of a chiral copper catalyst, substituted allylic iodides couple with α‐diazoesters to generate metal‐coordinated iodonium ylides, which undergo [2,3]‐rearrangements with high selectivities (up to >95:5 r.r., up to >95:5 d.r., and up to 97 %
ee ). The enantioenriched iodoester products can be converted stereospecifically into a variety of onium ylide rearrangement products, as well as compounds that are not accessible by classical onium ylide rearrangements. -
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Abstract A modular platform for facile access to 1,2,3,9‐tetrahydro‐4
H ‐carbazol‐4‐ones (H4‐carbazolones) and 3,4‐dihydrocyclopenta[b ]indol‐1(2H )‐ones (H2‐indolones) is described. The requisite 6‐ and 5‐membered 2‐arylcycloalkane‐1,3‐dione precursors were readily obtained through a Cu‐catalyzed arylation of 1,3‐cyclohexanediones or by a ring expansion of aryl succinoin derivatives. Enolization of one carbonyl group in the diones, conversion to a leaving group, and subsequent azidation gave 2‐aryl‐3‐azidocycloalk‐2‐en‐1‐ones. This two‐step, one‐pot azidation is highly regioselective with unsymmetrically substituted 2‐arylcyclohexane‐1,3‐diones. The regioselectivity, which is important for access to single isomers of 3,3‐disubstituted carbazolones, was analyzed mechanistically and computationally. Finally, a Rh‐catalyzed nitrene/nitrenoid insertion into theortho C−H bond of the aryl moiety gave the H4‐carbazolones and H2‐indolones. One carbazolone was elaborated to an intermediate reported in the total synthesis ofN ‐decarbomethoxychanofruticosinate, (−)‐aspidospermidine, (+)‐kopsihainanine A. With 2‐phenylcycloheptane‐1,3‐dione, prepared from cyclohexanone and benzaldehyde, the azidation reaction was readily accomplished. However, the Rh‐catalyzed reaction unexpectedly led to a labile but characterizable azirine rather than the indole derivative. Computations were performed to understand the differences in reactivities of the 5‐ and 6‐membered 2‐aryl‐3‐azidocycloalk‐2‐en‐1‐ones in comparison to the 7‐membered analogue, and to support the structural assignment of the azirine.
