skip to main content


Title: Refining boron–iodane exchange to access versatile arylation reagents
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.  more » « less
Award ID(s):
1856705 1828573
NSF-PAR ID:
10343350
Author(s) / Creator(s):
;
Date Published:
Journal Name:
Chemical Communications
Volume:
58
Issue:
8
ISSN:
1359-7345
Page Range / eLocation ID:
1211 to 1214
Format(s):
Medium: X
Sponsoring Org:
National Science Foundation
More Like this
  1. Abstract

    A direct and convenient method for the palladium‐catalyzed reductive cross‐coupling of aryl iodides or alkenyl bromides and secondary benzyl halides under ambient CO pressure to generate a diverse array of aryl/alkenyl alkyl ketones has been developed. This strategy successfully achieves a three‐component carbonylative reaction with Zn as the reducing agent for C−C bond formation, overcoming the well‐known homocoupling of aryl or alkenyl halides, direct cross‐coupling between two different electrophiles and other carbonylative coupling reactions. In addition, this method avoids use of preformed organometallic nucleophiles, such as organo‐magnesium, zinc and boron reagents. This approach enables the construction of valuable aryl alkyl/alkenyl ketone derivatives (60 examples, 56–95% yields). Reactivity studies indicate that in situ formed benzylic zinc reagents are intermediates in the catalytic system.

     
    more » « less
  2. null (Ed.)
    Construction of C–C bonds at the α-carbon is a challenging but synthetically indispensable approach to α-branched carbonyl motifs that are widely represented among drugs, natural products, and synthetic intermediates. Here, we describe a simple approach to generation of boron enolates in the absence of strong bases that allows for introduction of both α-alkyl and α-aryl groups in a reaction of readily accessible 1,2-dicarbonyls and organoboranes. Obviation of unselective, strongly basic and nucleophilic reagents permits carrying out the reaction in the presence of electrophiles that intercept the intermediate boron enolates, resulting in two new α-C–C bonds in a tricomponent process. 
    more » « less
  3. Abstract

    Main‐chain boron‐containing π‐conjugated polymers are attractive for organic electronic, sensing, and imaging applications. Alternating terthiophene‐borane polymers were prepared and the effects of regioisomeric attachment of the conjugated linker and variations in the electronic effect of the pendent aryl groups (2,4,6‐tri‐tert‐butylphenyl, Mes*; 2,4,6‐tris(trifluoromethyl)phenyl, FMes) examined. Pd2dba3/P(t‐Bu)3‐catalyzed Stille polymerization of arylbis(2‐thienyl)borane and arylbis(3‐thienylborane) with 2,5‐bis(trimethylstannyl)thiophene at 120 °C gave polymers with appreciable molecular weight but MALDI‐TOF MS analyses showed evidence of unusually prominent homocoupling. These defects could be suppressed by using brominated rather than iodinated monomers, more hindered 2,5‐bis(tri‐n‐butylstannyl)thiophene as comonomer, and Pd2dba3/P(o‐tol)3as the catalyst at 100 °C. Under these conditions, macrocyclic species withn=3–10 repeating units formed preferentially according to MALDI‐TOF MS analyses. Photophysical studies revealed a prominent effect of the regiochemistry and the nature of the pendent aryl groups on the absorption and emission, giving rise to orange, yellow‐green, blue‐green, and blue emissive materials respectively. The electronic effects were rationalized through DFT calculations on bis(terthiophene) model systems.

     
    more » « less
  4. Monomeric boroles have been gaining attention as reagents for the synthesis of heterocycles due to their ability to insert atoms into the BC 4 ring in a single step. Although unique boron frameworks can be accessed via this methodology, the products feature aryl substitution on the carbon centers as steric bulk is required to preclude borole dimerization. This work demonstrates that insertion chemistry is possible with Diels–Alder dimeric boroles and that such reactivity is not exclusive to monomeric boroles with bulky groups. With 1-phenyl-2,3,4,5-tetramethylborole dimer, the formal 1,1-insertion of a nitrene and sulfur generate the six-membered aromatic 1,2-azaborine and 1,2-thiaborine, respectively. The isolation of the 1,2-thiaborine enabled the synthesis of an η 6 -chromium complex. Benzophenone and diphenylketene readily insert a CO unit to generate BOC 5 seven-membered rings confirming dimeric boroles can serve as monomeric synthons in 1,2-insertion reactions. An epoxide did not furnish the anticipated eight-membered BOC 6 ring, instead provided a bicyclic system with a BOC 3 ring. The insertion chemistry was demonstrated with two other borole dimers featuring different substitution with diphenylketene as a substrate. This work elevates borole insertion chemistry to a new level to access products that do not require bulky substitution. 
    more » « less
  5. null (Ed.)
    We report the facile activation of aryl E–H (ArEH; E = N, O, S; Ar = Ph or C 6 F 5 ) or ammonia N–H bonds via coordination-induced bond weakening to a redox-active boron center in the complex, (1 − ). Substantial decreases in E–H bond dissociation free energies (BDFEs) are observed upon substrate coordination, enabling subsequent facile proton-coupled electron transfer (PCET). A drop of >50 kcal mol −1 in H 2 N–H BDFE upon coordination was experimentally determined. 
    more » « less