Tetrahedron Letters
Ionic liquid-mediated benzoyl transfer-coupling in the Suzuki and
Sonogashira reactions and aryl transfer-coupling by decarbonylative
Heck reaction, using N-Benzoyl-saccharin (NBSac) as reagent
Shruti S. Malunavar a, Suraj M. Sutar a, Pavankumar Prabhala a, Rajesh G. Kalkhambkar a, ,1
,
⇑
Kenneth K. Laali b,
⇑
,2
a Department of Chemistry, Karnatak University’s Karnatak Science College, Dharwad, Karnatak 580001, India
b Department of Chemistry, University of North Florida, 1, UNF Drive, Jacksonville, FL 32224, USA
a r t i c l e i n f o
a b s t r a c t
Article history:
The efficacy of N-benzoyl-saccharin (NBSac) as reagent for selective benzoyl transfer-coupling in the
Suzuki reaction in BMIM-IL/[PAIM][NTf2] as solvent/base, and in the Sonogashira reaction employing
guanidinium-IL (GIL) as solvent, are demonstrated. Decarbonylative aryl transfer-coupling occurs in
the Heck reaction employing GIL as solvent. The reactions are catalyzed by Pd(OAc)2 or NiCl2(dppp),
are performed under mild conditions in good yields, and have the potential for recycling/reuse of the
IL solvent. Collectively, these methods provide facile access to diverse libraries of diarylketones, keto-
ethynes and diaryl-ethenes.
Received 19 March 2020
Revised 14 April 2020
Accepted 27 April 2020
Available online 30 April 2020
Keywords:
Benzoylsaccharin
Benzoyl-transfer Suzuki and Sonogashira
coupling
Ó 2020 Elsevier Ltd. All rights reserved.
Decarbonylative Heck arylation
Guanidinium-IL (GIL)
BMIM-IL and PAIM-NTf2
Whereas N-halo-saccharins have been known as halogen
transfer reagents for over two decades [1], more recent discoveries
of N-functionalized saccharins bearing trifluoromethylthio (SCF3)
[2], formyl (CHO) [3,4], and acyl (RCO) [5,6] as functional group
transfer reagents have opened up new dimensions for their deploy-
ment in metal-mediated chemistry.
Focusing on N-benzoyl-saccharins as transfer benzoylation
reagents, two notable previous studies, namely the Suzuki cou-
pling via Pd-catalyzed N-acyl bond cleavage [5], and Heck arylation
via decarbonylation/arylation have been reported [6]. The Suzuki
coupling employed Pd along with PCy3HBF4, K2CO3 and H3BO3
for optimal performance with THF as solvent [5], while optimal
yields for the Heck coupling were reported with PdCl2 in NMP as
solvent at 160 °C.
benzoyl-transfer coupling in both the Suzuki and Sonogashira
reactions, and in the Heck reaction by decarbonylative aryl-
coupling. The Suzuki reaction employed [PAIM][NTf2] as the
basic-IL, [7f,7g] and [BMIM][PF6] or [BMIM][BF4] as solvent
(Fig. 1), whereas the Sonogashira reactions were performed in
ethylguanidinium ethylsulfate (GIL), [8] without the need for base
or any additive (Fig. 2).
Similarly, the Heck decarbonylative arylations were conve-
niently carried out in GIL as solvent (Fig. 3) without the need for
external base, CuX, or other additives.
All three types of transfer cross-coupling reactions were cat-
alyzed by either Pd or Ni in comparable yields, thus expanding
the catalytic scope of these transformations. The mild reaction con-
ditions employed, and recycling and reuse of the IL solvents pro-
vided additional benefits.
Table 1 summarizes the scope of the Suzuki coupling with
NBSac in IL employing various aromatic and alicyclic boronic acids,
[PAIM][NTf2] as basic-IL and [BMIM][X] as solvent, employing Pd
(OAc)2 or NiCl2(dppp) as catalyst, with isolated yields ranging from
88% to 82%, when using fresh IL, but with lower isolated yields
(81–63%) with the use of recycled ILs.
In continuation of our studies on synthetic and catalytic chem-
istry in ILs [7], and with our more recent emphasis on metal-medi-
ated cross-coupling reactions in imidazolium-ILs [7d]; [7f–7i], we
report here on the utility of N-benzoyl-saccharin (NBSac) for
⇑
Corresponding authors.
The scope of benzoyl-transfer coupling in the Sonogashira reac-
tion was examined by employing a diverse set of alkynes and the
results are summarized in Table 2. The reactions were performed
1
Tel.: +91 836 2215403; fax: +91836 2744334.
Tel.: +1 904 620 1503; fax: +1 904 620 3535.
2
0040-4039/Ó 2020 Elsevier Ltd. All rights reserved.