Copper-catalyzed Hiyama coupling of (hetero)aryltriethoxysilanes with (hetero)aryl iodides

Article abstract of DOI:10.1021/ol402701x

A Cu^I-catalyzed Hiyama coupling was achieved, which proceeds in the absence of an ancillary ligand for aryl-heteroaryl and heteroaryl-heteroaryl couplings. A P,N-ligand is required to obtain the best product yields for aryl-aryl couplings. In addition to facilitating transmetalation, CsF is also found to function as a stabilizer of the [CuAr] species, potentially generated as an intermediate after transmetalation of aryltriethoxysilanes with Cu ^I-catalysts in the absence of ancillary ligands.

Full text of DOI:10.1021/ol402701x

ORGANIC
LETTERS
XXXX
Vol. XX, No. XX
000–000
Copper-Catalyzed Hiyama Coupling
of (Hetero)aryltriethoxysilanes with
(Hetero)aryl Iodides
Santosh K. Gurung, Surendra Thapa, Adarsh S. Vangala, and Ramesh Giri*
Department of Chemistry & Chemical Biology, University of New Mexico, Albuquerque,
New Mexico 87131, United States
rgiri@unm.edu
Received September 19, 2013
ABSTRACT
A CuI-catalyzed Hiyama coupling was achieved, which proceeds in the absence of an ancillary ligand for arylꢀheteroaryl and heteroarylꢀ
heteroaryl couplings. A P,N-ligand is required to obtain the best product yields for arylꢀaryl couplings. In addition to facilitating transmetala-
tion, CsF is also found to function as a stabilizer of the [CuAr] species, potentially generated as an intermediate after transmetalation of
aryltriethoxysilanes with CuI-catalysts in the absence of ancillary ligands.
Hiyama coupling remains an indispensable synthetic
tool for theconstructionofCꢀC bondsinnatural products
and pharmaceutical molecules.1 This transformation of-
fers a unique advantage over other organometallic-based
cross-coupling processes owing to its exploitation of organo-
silicon reagents, which are advantaged due to their ease
of synthesis, handling, high stability, and low toxicity.2
The pragmatic application of the Hiyama coupling in the
contexts of constructing complex molecules was fur-
ther reinforced by the Denmark1d,3 and DeShong1e,f groups
with the use of organosilicon reagents in both the presence
and absence of fluoride sources. Despite the synthetic
appealstendered by the organosiliconcompounds, Hiyama
coupling is typically conducted with Pd-based catalysts.
Nonetheless, remarkable reports from the Fu group on
Ni-catalyzed couplings of aryltrialkoxysilanes with alkyl
halides4 have raised anticipation that the Hiyama coupling
could now be conducted with non-noble metals with a high
level of efficacy.5 Moreover, the Ball group has recently
demonstrated that aryl/allyltrialkoxysilanes undergo facile
transmetalation with (NHC)Cu(F) (NHC = N-heterocyclic
carbene) to generate (NHC)Cu(Ar/allyl) complexes.6
(5) For examples of Cu-catalyzed SuzukiꢀMiyaura coupling, see: (a)
Thathagar, M. B.; Beckers, J.; Rothenberg, G. J. Am. Chem. Soc. 2002,
124, 11858. (b) Li, J.-H.; Li, J.-L.; Wang, D.-P.; Pi, S.-F.; Xie, Y.-X.;
Zhang, M.-B.;Hu, X.-C. J. Org. Chem. 2007, 72, 2053. (c)Li, J.-H.;Wang,
D.-P. Eur. J. Org. Chem. 2006, 2006, 2063. (d) Li, J. H.; Li, J. L.; Xie, Y. X.
Synthesis 2007, 984. (e) Mao, J. C.; Guo, J.; Fang, F. B.; Ji, S. J.
Tetrahedron 2008, 64, 3905. (f) Ye, Y. M.; Wang, B. B.; Ma, D.; Shao,
L. X.; Lu, J. M. Catal. Lett. 2010, 139, 141. (g) Yang, C.-T.; Zhang, Z.-Q.;
Liu, Y.-C.; Liu, L. Angew. Chem., Int. Ed. 2011, 50, 3904. (h) Lipshutz,
B. H.; Nihan, D. M.; Vinogradova, E.; Taft, B. R.; Bogkovic, Z. V. Org.
Lett. 2008, 10, 4279. For examples of Cu-catalyzed Stille coupling, see: (i)
Takeda, T.; Matsunaga, K.-I.; Kabasawa, Y.; Fujiwara, T. Chem. Lett.
1995, 24, 771. (j) Falck, J. R.; Bhatt, R. K.; Ye, J. J. Am. Chem. Soc. 1995,
117, 5973. (k)Allred, G. D.;Liebeskind, L. S. J. Am. Chem. Soc. 1996, 118,
2748. (l) Kang, S.-K.; Kim, J.-S.; Choi, S.-C. J. Org. Chem. 1997, 62, 4208.
(m) Nudelman, N. S.; Carro, C. Synlett 1999, 1942.
(1) (a) Chang, W.-T. T.; Smith, R. C.; Regens, C. S.; Bailey, A. D.;
Werner, N. S.; Denmark, S. E. Org. React. 2011, 75, 213. (b) Sore, H. F.;
Galloway, W. R. J. D.; Spring, D. R. Chem. Soc. Rev. 2012, 41, 1845. (c)
Hiyama, T. J. Organomet. Chem. 2002, 653, 58. (d) Denmark, S. E.; Liu,
J. H. C. Angew. Chem., Int. Ed. 2010, 49, 2978. (e) Handy, C. J.; Manoso,
A. S.; McElroy, W. T.; Seganish, W. M.; DeShong, P. Tetrahedron 2005,
61, 12201. (f) Shukla, K. H.; DeShong, P. Heterocycles 2012, 86, 1055.
(2) Nakao, Y.; Hiyama, T. Chem. Soc. Rev. 2011, 40, 4893.
(3) Denmark, S. E.; Sweis, R. F. J. Am. Chem. Soc. 2001, 123, 6439.
(4) (a) Powell, D. A.; Fu, G. C. J. Am. Chem. Soc. 2004, 126, 7788. (b)
Strotman,N.A.;Sommer,S.;Fu,G.C.Angew. Chem., Int. Ed. 2007,46, 3556.
(c) Dai, X.; Strotman, N. A.; Fu, G. C. J. Am. Chem. Soc. 2008, 130, 3302.
(6) (a) Herron, J. R.; Ball, Z. T. J. Am. Chem. Soc. 2008, 130, 16486.
(b) Herron, J. R.; Russo, V.; Valente, E. J.; Ball, Z. T. Chem.;Eur. J.
2009, 15, 8713. (c) Russo, V.; Herron, J. R.; Ball, Z. T. Org. Lett. 2009,
12, 220.
r
10.1021/ol402701x
XXXX American Chemical Society

However, the resultant organocopper species were shown to
be reactive only toward aldehydes, acyl halides, and allylic
substrates.6 Transmetalation of ArSiF3 with (NHC)Cu(Br)
in the presence of a fluoride source to generate (NHC)Cu(Ar)
species was also proposed previously by the Hoveyda group7
in the conjugate addition of ArSiF3 to cyclic enones.8 In
addition, Cu-salts are known to improvethe product yields
in Pd-catalyzed Hiyama couplings.9 A previous report10
showed that [CuOC6F6] could mediate the coupling of
arylsilicon reagents with aryl iodides but with limited
substrates and required a stoichiometric amount of the
copper salt.11 Herein, we report the first Cu-catalyzed
Hiyama coupling of aryl- and heteroaryltriethoxysilanes
with aryl- and heteroaryl iodides, a transformation that
proceeds, depending upon the types of substrates, with and
without requiring the addition of ligands for the best
product yields. In addition, we have demonstrated a dual
role for CsF, one as a fluoride source to facilitate the trans-
metalation of ArSi(OEt)3 with CuI, and the other as a
stabilizer of monomeric [CuAr] species by preventing
aggregation in reactions that are conducted in the absence
of a ligand.
Our investigation began with the selection of different
ligands in conjunction with CuI for screening reaction
conditions in an attempt to couple arylsilicon reagents
with p-iodotoluene (Table 1). We found that the reaction
of PhSi(OEt)3 (a1) with p-iodotoluene (b1) proceeded in
the presence of a bidentate ligand PN-1 in 24 h in DMF
at 120 °C to afford 4-phenyltoluene (c1) in good yield
(60% by GC, entry 1) when CsF was utilized as a fluoride
source. Other similar P,N-ligands (see Supporting Infor-
mation (SI) for details) provided the product c1 in lower
yields (entry 2). To our surprise, the reaction of a1 with
p-iodotoluene proceeded even in the absence of PN-1,
albeit providing the biaryl product in only 40% GC
yield (entry 3). Replacing CuI with CuOtBu (purified by
sublimation)12 generated the product in 50% GC yield
(entry 4). The reaction does not proceed in the absence of
either the Cu-catalyst or CsF and affords the product in
<5% yield when CsF is replaced with other Fꢀ sources
(entries 5ꢀ7). Replacing a1 with PhSiMe3 yielded no
product at all (entry 8). Similarly, utilizing p-bromo- or
p-chlorotoluene as an aryl halide afforded only trace
amounts of the product (entry 9). Use of NMP and HMPA
as solvents provided the product in 30% and 40% GC
yields, respectively (entries 10, 11). Other solvents such as
DMSO, dioxane, toluene, or MeCN produced 4-phenyl-
toluene in <5% yield (entry 12).
Table 1. Optimization of Reaction Conditionsa
entry
modified conditions
standard conditions
yield (%)b
1
2
3
4
5
6
7
8
9
60 (55)c
PN-2ꢀPN-5 (see SI for details)
without ligand
45ꢀ50
40
50
0
with CuOtBu (sublimed) instead of CuI
without CuI
without CsF
0
LiF, NaF, KF, RbF, or TBAF instead of CsF
PhSiMe3 instead of PhSi(OEt)3
4-bromo- or 4-chlorotoluene instead of
4-iodotoluene
<5
0
<2
10
11
12
NMP instead of DMF
30
40
<5
HMPA instead of DMF
DMSO, dioxane, toluene, or MeCN instead
of DMF
a Reactions were run on a 0.1 mmol scale in 0.5 mL of anhydrous
DMF. CuI (99.999%) and CsF (99.9%) were used in all reactions.
b Calibrated GC yields using 2-nitrobiphenyl as a standard. c Number in
parentheses is the isolated yield from a 1.0 mmol scale reaction. Less
than 3% homocoupling products were observed. ∼30% unreacted
starting materials was observed based on GC.
(7) Lee, K. S.; Hoveyda, A. H. J. Org. Chem. 2009, 74, 4455.
(8) For the existence of similar organocopper species in the presence of
organosilicon reagents, see: (a) Miki, Y.; Hirano, K.; Satoh, T.; Miura, M.
Org. Lett. 2012, 15, 172. (b) Franz, A. K.; Woerpel, K. A. J. Am. Chem.
Soc. 1999, 121, 949. (c) Taguchi, H.; Ghoroku, K.; Tadaki, M.; Tsubouchi,
A.; Takeda, T. J. Org. Chem. 2002, 67, 8450. (d)Taguchi, H.; Ghoroku, K.;
Tadaki, M.; Tsubouchi, A.; Takeda, T. Org. Lett. 2001, 3, 3811. (e)
Tomita, D.; Wada, R.; Kanai, M.; Shibasaki, M. J. Am. Chem. Soc.
2005, 127, 4138. (f) Yamasaki, S.; Fujii, K.; Wada, R.; Kanai, M.;
Shibasaki, M. J. Am. Chem. Soc. 2002, 124, 6536. (g) Lam, P. Y. S.;
Deudon, S.;Averill, K. M.;Li, R. H.;He, M. Y.;DeShong, P.;Clark, C. G.
J. Am. Chem. Soc. 2000, 122, 7600. (h) Lin, B.; Liu, M.; Ye, Z.; Ding, J.;
Wu, H.; Cheng, J. Org. Biomol. Chem. 2009, 7, 869.
(9) For effects of Cu-salts on reactions involving organosilicon
reagents, see: (a) Denmark, S. E.; Baird, J. D. Org. Lett. 2004, 6, 3649.
(b) Hanamoto, T.; Kobayashi, T.; Kondo, M. Synlett 2001, 2001, 0281.
(c) Nakao, Y.; Imanaka, H.; Sahoo, A. K.; Yada, A.; Hiyama, T. J. Am.
Chem. Soc. 2005, 127, 6952. (d) Nakao, Y.; Takeda, M.; Matsumoto, T.;
Hiyama, T. Angew. Chem., Int. Ed. 2010, 49, 4447.
After establishing the optimal conditions (Table 1), we
examined the substrate scope of the new cross-coupling
protocol. The current conditions allow the reactions to
proceed for arylꢀaryl, arylꢀheteroaryl, and heteroarylꢀ
heteroaryl couplings in good to excellent product yields
(Tables 2, 3). The reactions conducted in the presence of
the ligand PN-1 consistently provided good yields of
products for the couplings of aryltriethoxysilanes with aryl
iodides (Table 2). The use of PN-1 increased the yields of
the arylꢀaryl coupling products by 20ꢀ54% relative to
that of the reactions conducted without the ligand (entries
3, 6, 15). Similarly, a variety of functional groups were
tolerated on the aryl rings of both the aryltriethoxysilanes
and the aryl iodides. Reactions proceed well with electron-
deficient and -rich aryl rings on both coupling partners.
Halogen, exemplified using chloride, is also tolerated
on both the aryltriethoxysilanes and the aryl iodides
(entries 8ꢀ10).
(10) Ito, H.; Sensui, H.; Arimoto, K.; Miura, K.; Hosomi, A. Chem.
Lett. 1997, 26, 639.
(11) For homocouplings of vinyl-, alkynyl-, and arylsilicon reagents
with stoichiometric amounts of copper salts, see: (a) Nishihara, Y.;
Ikegashira, K.; Toriyama, F.; Mori, A.; Hiyama, T. Bull. Chem. Soc.
€
Jpn. 2000, 73, 985. (b) Louerat, F.; Gros, P. C. Tetrahedron Lett. 2010, 51,
3558. (c) Itami, K.; Ushiogi, Y.; Nokami, T.; Ohashi, Y.; Yoshida, J.-I.
Org. Lett. 2004, 6, 3695. (d) Ikegashira, K.; Nishihara, Y.; Hirabayashi,
K.; Mori, A.; Hiyama, T. Chem. Commun. 1997, 1039.
(12) Lemmen, T. H.; Goeden, G. V.; Huffman, J. C.; Geerts, R. L.;
Caulton, K. G. Inorg. Chem. 1990, 29, 3680.
B
Org. Lett., Vol. XX, No. XX, XXXX

Surprisingly, PN-1 showed a detrimental effect on arylꢀ
heteroaryl and hetereoarylꢀheteroaryl couplings and de-
creased the product yields by 14ꢀ34% relative to that of
the reactions performed without PN-1 (Table 3, entries 3,
4, 7, 8). We believe that the pyridine rings of the heteroaryl
iodides, which act as secondary ligands in excess, bind to
CuI already ligated to the bidentate ligand PN-1, effec-
tively slowing down the approach of the CꢀI bond of
heteroaryl iodides to the Cu-catalyst for activation. The
omission of PN-1 from the reaction system, however,
creates vacant sites on CuI which are only occupied by
the monodentate pyridine rings in a readily reversible
process. Therefore, the reactions for arylꢀheteroaryl and
heteroarylꢀheteroaryl couplings were conducted with-
out PN-1. Aryl-heteroaryl couplings tolerate a variety of
functional groups and proceed well with electron-deficient
and -rich aryl rings on both coupling partners. Coupling of
2-thienylsilane a6 with electron-deficient aryl and hetero-
aryl iodides provided products in good to excellent yields
(entries 12ꢀ22). Both arylꢀheteroaryl and heteroarylꢀ
heteroaryl couplings tolerate halides such as chloride and
bromide either on both coupling partners or on the aryl
iodides.
Based on our preliminary mechanistic studies and pre-
vious reports, we have proposed a catalytic cycle (Scheme 1)
for the present CuI-catalyzed Hiyama coupling.13 Under
ligand-free conditions, iodide from the solvated CuI (e1,
LL = solv) is displaced in the initial step by the fluoride
anion from CsF to generate a solvated CuF species (e2,
LL = solv), which then undergoes transmetalation with
ArSi(OEt)3 to generate a solvated monomeric [CuAr] inter-
mediate (e3, LL = solv).6a However, a mechanistic scenario
reminiscent of the Pd-catalyzed Hiyama coupling, where the
ligated CuI directly undergoes transmetalation with the
fluoride-activated ArSi(OEt)3, also cannot be ruled out at
this moment.2 In either scenario, once the solvated mono-
meric [CuAr] species e3 is generated it is expected to react
with aryl halides14 to form a cross-coupled product (Table 4,
entry 1). However, when the [CuPh] complex15 was reacted
with p-iodotoluene under our reaction conditions, a pre-
dominant amount of the homocoupling product d1 and
only traces of the cross-coupled product c1 were formed
(entry 2). Surprisingly, when CsF was added to the reaction,
a higher yield of the cross-coupled product c1 was formed
(entry 3). It is known that the isolated arylcopper species
remain as aggregates, typically as tetramers, rather than as
monomers.16 Therefore, we presumed that such aggregates
could possibly be unreactive toward aryl halides and that
CsF disaggregates the arylcopper species, possibly by
Table 2. Coupling of Aryltriethoxysilanes with Aryl Iodides in
the Presence of PN-1a
a Reactions were run under the standard conditions from Table 1,
entry 1 in 1.0 mmol scale for 24 h. b Isolated yields. Numbers in
parentheses represent isolated yields in the absence of PN-1.
Table 3. Coupling of Aryl- and Heteroaryltriethoxysilanes with
Aryl and Heteroaryl Iodides in the Absence of PN-1a
(13) For X-ray structure of [(PN-1)CuI]2, see: Wesemann, L. K.;
Fritz-Robert, K.; Mayer, H. A.; Wernitz, S.; Yersin, H.; Leitl, M. PCT
Int. Appl. (2013), WO 2013014066 A1 20130131.
(14) Nilsson, M.; Wennerstrom, O. Acta Chem. Scand. 1970, 24, 482.
(15) Costa, G.; Camus, A.; Gatti, L.; Marsich, N. J. Organomet.
Chem. 1966, 5, 568.
(16) (a) Meyer, E. M.; Gambarotta, S.; Floriani, C.; Chiesivilla, A.;
Guastini, C. Organometallics 1989, 8, 1067. (b) Van Koten, G.; Jastrzebski,
J. T. B. H.; Muller, F.; Stam, C. H. J. Am. Chem. Soc. 1985, 107, 697. (c)
Van Koten, G.; Jastrzebski, J. T. B. H.; Noltes, J. G. J. Organomet. Chem.
1977, 140, C23. (d) Hope, H.; Oram, D.; Power, P. P. J. Am. Chem. Soc.
1984, 106, 1149.
a Reactions were run with the conditions from Table 1, entry 3 in
1.0 mmol scale for 12 h in the absence of PN-1. <3% homocoupling
products observed in most cases. b Isolated yields. Numbers in parenthe-
ses represent isolated yields in the presence of PN-1.
Org. Lett., Vol. XX, No. XX, XXXX
C

Table 4. Reactions of Independently Synthesized [CuPh]
Complex with p-Iodotoluenea
Scheme 1. Proposed Catalytic Cycle
entry
additive
ref 14c
yield (%) (c1/d1)b
1
2
3
4
36/36d
3/40
none
CsF (0.15 mmol)
PN-1 (0.05 mmol)
44/14
43/6
a Reactions were run with [CuPh] (0.05 mmol) and p-iodotoluene
(0.10 mmol) in 0.5 mL of DMF. b Calibrated GC yields. Less than 3% of
4,40-bitolyl was also formed. c 4-Iodoanisole was used instead of b1 in
pyridine as a solvent at 50 °C for 47 h. d Yields of 4-methoxybiphenyl and
d1. 10% 4,40-dimethoxybiphenyl was also reported.
Scheme 2. Test for an Aryl Radical Intermediate
forming a monomeric cuprate complex e4 as a resting-state
species.17 The complex e4 could slowly equilibrate to the
reactive monomeric species e3 (LL = solv) during reaction
(Scheme 1).18 Since the reaction conducted without a ligand
generates only trace amounts of homocoupling products,
we believe that the reaction proceeds via a monomeric,
solvated [CuAr] species e3 and that CsF plays a second role,
in addition to facilitating transmetalation, as a stabilizer for
(solv)Cu(Ar) should this species begin to aggregate during
reaction.19
In addition, [CuPh] affords a significant amount of the
cross-coupled product c1 in the presence of PN-1 (Table 4,
entry 4), suggesting that the binding of the ligand also
facilitates disaggregation of polymeric [CuPh]20 and con-
verts it to a ligated, reactive species (Scheme 1, e3, LL =
PN-1).21 A brief study of the reaction of PhSi(OEt)3 with
the radical probe b21 showed that only the cross-coupled
product c2 was formed (Scheme 2).5g,21a The cyclized
product d2, as expected to arise from a corresponding aryl
radical, was not detected when the reaction mixture was
analyzed by GC,22 indicating that the reaction does not
involve aryl radical intermediates.
In summary, we have developed the first CuI-catalyzed
Hiyama coupling of aryl- and heteroaryltriethoxysilanes
with aryl and heteroaryl iodides, which provides the best
product yields in the presence or absence of ligands for
arylꢀaryl, arylꢀheteroaryl, and heteroarylꢀheteroaryl
couplings, respectively. The reaction tolerates a variety of
functional groups on both coupling partners. We have also
conducted preliminary mechanistic studies with a radical
probe and an independently synthesized [CuPh] complex
and proposed a catalytic cycle. During our studies, we
unraveled a second role for CsF as a stabilizer of [CuAr]
intermediates in the absence of ligands in addition to its
typical role as a fluoride source to facilitate transmetala-
tion of the organosilicon reagents with CuI.
(17) For structures of analogous, diarylcuprates with lithium as a
countercation, see: (a) Lorenzen, N. P.; Weiss, E. Angew. Chem., Int. Ed.
1990, 29, 300. (b) Hope, H.; Olmstead, M. M.; Power, P. P.; Sandell, J.;
Xu, X. J. Am. Chem. Soc. 1985, 107, 4337. (c) Bertz, S. H.; Dabbagh, G.
J. Am. Chem. Soc. 1988, 110, 3668.
(18) Similar lithium diarylcuprates react with aryl iodides only in the
presence of O2. See: Whitesides, G. M.; Fischer, W. F.; San Filippo, J.;
Bashe, R. W.; House, H. O. J. Am. Chem. Soc. 1969, 91, 4871.
(19) As suggested by a reviewer, we followed the 19F NMR signal of
CsF in DMF in the presence of [CuPh] at room temperature. A sharp
singlet of CsF at δ ꢀ148.0 ppm shifted upfield to δ ꢀ222.0 ppm as a
broad singlet, but the identity of the new species could not be determined
unambiguously (see Supporting Information for details).
(20) For examples of ligated [CuAr] complexes, see: (a) Leoni, P.;
Pesquali, M.; Ghilardi, C. A. J. Chem. Soc., Chem. Commun. 1983, 240.
(b) Do, H. O.; Khan, R. M. K.; Daugulis, O. J. Am. Chem. Soc. 2008,
130, 15185. (c) Doshi, A.; Sundararaman, A.; Venkatasubbaiah, K.;
Zakharov, L. N.; Rheingold, A. L.; Myahkostupov, M.; Piotrowiak, P.;
Acknowledgment. We thank the University of New
Mexico for financial support, and the UNM NMR (NSF
Grant No. 0946690) and Mass Spectrometry Facilities for
high resolution mass and NMR data.
€
Jakle, F. Organometallics 2011, 31, 1546.
(21) For similar mechanistic scenarios proposed for CuI-catalyzed
C-X couplings, see: (a) Tye, J. W.; Weng, Z.; Johns, A. M.; Incarvito,
C. D.; Hartwig, J. F. J. Am. Chem. Soc. 2008, 130, 9971. (b) Strieter,
E. R.; Blackmond, D. G.; Buchwald, S. L. J. Am. Chem. Soc. 2005, 127,
4120. (c) Giri, R.; Hartwig, J. F. J. Am. Chem. Soc. 2010, 132, 15860.
(22) The o-allyloxyphenyl radical generated from the radical probe
b21 is known to cyclize in DMSO at 23 °C to give the cyclized product d2
with a kobs of 9.6 ꢁ 109 sꢀ1. See: Annunziata, A.; Galli, C.; Marinelli, M.;
Pau, T. Eur. J. Org. Chem. 2001, 1323.
Supporting Information Available. Experimental pro-
cedures, characterization data, and the NMR spectra of
new compounds. This material is available free of charge
via the Internet at http://pubs.acs.org.
The authors declare no competing financial interest.
D
Org. Lett., Vol. XX, No. XX, XXXX