Direct Synthesis of Terminal Alkynes via Pd-Catalyzed Cross Coupling of Aryl and Alkenyl Halides with Ethynylmetals Contang Zn, Mg, and Sn. Critical Comparison of Countercations

Full text of DOI:10.1021/jo971552b

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J . Org. Chem. 1997, 62, 8957-8960
8957
Sch em e 1
Dir ect Syn th esis of Ter m in a l Alk yn es via
P d -Ca ta lyzed Cr oss Cou p lin g of Ar yl a n d
Alk en yl Ha lid es w ith Eth yn ylm eta ls
Con ta in in g Zn , Mg, a n d Sn . Cr itica l
Com p a r ison of Cou n ter ca tion s
Ei-ichi Negishi,* Martin Kotora, and Caiding Xu
Department of Chemistry, Purdue University,
West Lafayette, Indiana 47907-1393
Received August 19, 1997
to the Pd-catalyzed direct ethynylation of phenyl iodide.
The experimental results summarized in Table 1 indicate
the following. Ethynylmetals containing Mg, Zn, and Sn
provide phenylacetylene in nearly quantitative yields,
although the reaction of ethynyltributyltin was substan-
tially slower than the other two. Ethynylsodium is not
a satisfactory reagent under the comparable conditions.
The total failure observed with lithium ethynyltrieth-
ylborate generated in situ from ethynyllithium and Et3B
was quite puzzling in view of our earlier favorable results
observed with lithium 1-heptynyltributylborate.5 Using
the same batch of Et3B, we ran two parallel reactions of
LiBEt3(CtCH) and LiBEt3(CtCHex-n) with PhI in the
presence of 5 mol % of Pd(PPh3)4 and obtained PhCtCH
and PhCtCHex-n in <5 and 80% yields, respectively.
Although no further insight into the reaction of LiBEt3-
(CtCH) is available at this time, we tentatively conclude
that ethynyltrialkylborates are not suitable reagents for
the synthesis of terminal alkynes. Ethynylzinc deriva-
tives are readily generated in situ by treatment of
ethynyllithium (which in turn may be generated by
treatment of acetylene with n-BuLi8) or, more conve-
niently, commercially available ethynylmagnesium bro-
mide, the corresponding chloride, or ethynylsodium in
xylene/mineral oil with dry ZnBr2 or ZnCl2. The use of
PhBr in place of PhI did not lead to the formation of
PhCtCH under otherwise the same conditions. The use
of Cl2Pd(PPh3)2 did not offer any advantage over Pd-
(PPh3)4.
Although Mg, Zn, and Sn are comparably satisfactory
in the ethynyl-phenyl coupling (Table 1), further delin-
eation of the scope of the Pd-catalyzed ethynyl-aryl
coupling revealed some critical limitations associated
with Mg and Sn (Table 2). Ethynylmagnesium bromide
appears to be as satisfactory as ethynylzinc bromide in
cases where substituents do not readily react with
HCtCMgBr and/or sterically interfere with the desired
cross coupling. However, at least two kinds of limitations
associated with HCtCMgBr should be noted. The reac-
tions of p-nitrophenyl iodide and methyl p-iodobenzoate
clearly reveal expected chemoselectivity problems associ-
ated with Mg. A more subtle limitation associated with
Mg is competitive formation of diarylethynes, which must
arise via H-Mg exchange. There appear to be at least
two contributing factors: (i) higher ionicity of the C-Mg
bond relative to the C-Zn bond rendering the former
more prone to H-Mg exchange and (ii) slower cross
coupling rates observed with Grignard reagents relative
to the corresponding organozincs. Although not yet
clearly demonstrated, one may additionally expect that
the formation of a terminal alkyne having a higher
acidity than the starting acetylene would also favor the
formation of ArCtCAr. Since HCtCSnBu3 is more
Several Pd-catalyzed cross-coupling procedures for the
synthesis of alkynes were reported in the mid 1970s.1-5
Of these, the Sonogashira protocol3 involving the treat-
ment of terminal alkynes with organic halides and an
amine base, e.g., Et2NH, in the presence of catalytic
quantities of a Pd-phosphine complex and CuI has been
most widely used presumably due to generally favorable
results and operational simplicity associated with it. One
of its serious limitations, however, is its reported in-
ability3 to provide a direct route to terminal alkynes. We
have indeed confirmed this by running the reaction of
PhI with an excess of acetylene in the presence of 5 mol
% each of Pd(PPh3)4 and CuI, which gave PhCtCPh in
40% yield along with only a 20% yield of the desired
PhCtCH. Thus, a selective synthesis of terminal alkynes
by this method requires an indirect route involving
protection and deprotection of the ethynyl group.3b,6 We
earlier reported a few examples of a direct synthesis of
terminal alkynes via Pd-catalyzed cross coupling of
HCtCZnCl with organic halides,4 using mainly a cylin-
der of acetylene as the source of the ethynyl group. In
view of the growing significance of the Pd-catalyzed
synthesis of alkynes, we sought practically convenient,
direct, and chemoselective routes to terminal alkynes,
and we herein report that HCtCZnBr (or Cl) generated
in situ from commercially available HCtCMgBr (or Cl)
and HCtCNa can readily cross couple with a variety of
aryl and alkenyl iodides (and bromides in some cases) in
the presence of a Pd-phosphine catalyst, e.g., Pd(PPh3)4,
to produce directly and selectively the corresponding
terminal alkynes in high yields (Scheme 1). We further
present a critical comparison of countercations including
Zn, Mg, Sn, and B.
In our earlier studies4,5 we reported the first set of
examples of the successful use of alkynylmetals contain-
ing Mg, Zn, B, Al, and Sn in the Pd-catalyzed alkyne
synthesis. On the other hand, alkynyllithiums were
generally unsatisfactory,7 even though alkynylsodiums
were reported to be satisfactory.1 In the current study,
we first screened Li, Na, Mg, Zn, B, and Sn with respect
(1) Cassar, L. J . Organomet. Chem. 1975, 93, 253.
(2) Dieck, H. A.; Heck, R. F. J . Organomet. Chem. 1975, 93, 259.
(3) (a) Sonagashira, K.; Tohda, T.; Hagihara, N. Tetrahedron Lett.
1975, 4467. (b) Takahashi, S.; Kuroyama, Y.; Sonogashira, K.;
Hagihara, N. Synthesis 1980, 627.
(4) (a) King, A. O.; Okukado, N.; Negishi, E. J . Chem. Soc., Chem.
Commun. 1977, 683. (b) King, A. O.; Negishi, E.; Villani, F. J ., J r.;
Silveira, A., J r. J . Org. Chem. 1978, 43, 358.
(5) (a) Negishi, E. In Aspects of Mechanism and Organometallic
Chemistry; Brewster, J . H., Ed.; Plenum Press: New York, 1978; p
285. See also: Negishi, E. Acc. Chem. Res. 1982, 15, 340. (b) For the
use of alkynylmagnesium derivatives, see also: Dang, H. P.; Lin-
strumelle, G. Tetrahedron Lett. 1978, 191.
(6) Ames, D. E.; Bull, D.; Takundwa, C. Synthesis 1981, 364.
(7) For a later study demonstrating an inhibitory action of alkyl-
lithiums, see: Negishi, E.; Akiyoshi, K.; Takahashi, T. J . Chem. Soc.,
Chem. Commun. 1987, 477.
(8) Midland, M. M. J . Org. Chem. 1975, 40, 2250.
S0022-3263(97)01552-1 CCC: $14.00 © 1997 American Chemical Society

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8958 J . Org. Chem., Vol. 62, No. 25, 1997
Notes
Ta ble 1. P d -Ca ta lyzed Cr oss Cou p lin g of P h en yl Iod id e
w ith Eth yn ylm eta ls
sodium benzophenone ketyl. DMF was freshly distilled and
dried over 4A molecular sieve. ZnBr2 was flame-dried under
vacuum. HCtCMgBr, HCtCMgCl, HCtCNa, and HCtCLi‚
EDA were obtained from Aldrich. HCtCSnBu3 was prepared
by the reaction HCtCMgBr (or Cl) with ClSnBu3 in THF.
HCtCB(Bu-n)3Na(or Li) was prepared by the reaction of B(Bu-
n)3 with HCtCNa (or Li) in THF. Pd(PPh3)4,9 PdCl3(PPh2)2,10
(E)-1-iodo-1-octene,11 (E)-4-iodo-4-octene,12 and (E)-1-iodo-2-
methyl-1-octene13 were prepared as reported in the literature.
Iodomesitylene was prepared from bromomesitylene by lithiation
followed by iodinolysis. All other aryl iodides were obtained from
commercial sources.
(E)-4-Iod o-5-m eth yl-4-octen e. This compound was pre-
pared as reported previously13 except for the reaction temper-
ature of 22 °C. When the reaction was carried out at 50 °C for
6 h, as specified earlier,13 a mixture of the E- and Z-isomers
resulted. The procedure used in this study is as follows. To a
suspension of Cl2ZrCp2 (2.92 g, 10 mmol) in 1,2-dichloromethane
(25 mL) was added Me3Al (1.44 g, 1.92 mL, 20 mmol) (pyro-
phoric!) under argon at 22 °C. All Cl2ZrCp2 dissolved within
10-15 min to give a lemon-yellow solution. To this was added
1.10 g (1.47 mL, 10 mmol) of 4-octyne. After the solution was
stirred for 6 h at 22 °C, 3.05 g (12 mmol) of iodine dissolved in
15 mL of THF was added at 0 °C. After the iodine color faded,
the reaction mixture was quenched with water-ether, and the
organic layer was separated, washed with aqueous Na2S2O3,
dried over MgSO4, filtered, and distilled to give 2.01 g (82%) of
(E)-4-iodo-5-methyl-4-octene: 1H NMR (CDCl3, Me4Si) δ 0.90 (t,
J ) 7.4 Hz, 6 H), 1.4-1.7 (m, 4 H), 1.91 (s, 3 H), 2.1-2.3 (m, 2
H), 2.50 (t, J ) 7.4 Hz, 2 H) ppm; 13C NMR (CDCl3, Me4Si) δ
12.96, 13.84, 21.53, 23.01, 29.75, 35.68, 42.93, 104.76, 139.99
ppm; stereoisomer purity >98%.
P d -Ca t a lyzed Cr oss Cou p lin g of Ar yl Iod id es w it h
Eth yn ylm eta ls. (a ) Rea ction of 2-Iod o-p-xylen e with Eth y-
n ylzin c Br om id e. Rep r esen ta tive P r oced u r e for th e Use
of Eth yn ylzin c Br om id e. To a flame-dried 50-mL flask
equipped with a magnetic stirring bar were sequentially added
under an Ar atmosphere HCtCZnBr, 2-iodo-p-xylene (464 mg,
2 mmol), and Pd(PPh3)4 (115 mg, 0.1 mmol). A solution of
HCtCZnBr was prepared by the reaction of HCtCMgBr (3
mmol, 6 mL of 0.5 M solution in THF) with dry ZnBr2 (675 mg,
3 mmol) dissolved in 5 mL of THF. The course of reaction was
monitored by gas chromatography, and the reaction was com-
plete in 3 h at 22 °C. The reaction mixture was quenched with
aqueous NaCl, extracted with Et2O, dried over MgSO4, and
concentrated in vacuo. Column chromatography on silica gel
afforded 2-ethynyl-p-xylene14 (220 mg, 85%): 1H NMR (CDCl3,
Me4Si) δ 2.26 (s, 3 H), 2.39 (s, 3 H), 3.22 (s, 1 H), 6.9-7.3 (m, 3
H) ppm; 13C NMR (CDCl3, Me4Si) δ 20.02, 20.64, 80.47, 82.70,
121.63, 129.30, 129.59, 132.92, 134.94, 137.58 ppm. (b) Rea c-
tion of 2-Iod o-p-xylen e w ith Eth yn ylm a gn esiu m Br om id e.
This reaction was carried out in the same manner as above
except that HCtCMgBr was used and that the reaction time
was 48 h. (c) Rea ction of 2-Iod o-p-xylen e w ith Eth yn yl-
tr ibu tyltin . This reaction was carried out in the same manner
as above except that HCtCsn(Bu-n)3 was used and that the
reaction time was 24 h.
a
b
By NMR or GLC. Diphenylacetylene was formed in 2% yield.
c Generated in situ from HCtCNa and ZnBr2. Generated in situ
from HCtCMgCl and ZnBr2. e Generated in situ from HCtCMgCl
and ClSnBu3. f Generated in situ from HCtCLi and B(Bu-n)3.
d
g
Generated in situ from HCtCNa and B(Bu-n)3.
expensive than HCtCMgBr or HCtCZnBr and since its
use requires more cumbersome isolation and purification
procedures, there generally is little incentive for using
HCtCSnBu3. Its significantly lower reactivity relative
to HCtCZnBr, as demonstrated in the reaction of mesityl
iodide, is yet another limitation associated with Sn.
Finally, the scope of the Pd-catalyzed ethynyl-alkenyl
coupling was investigated. As the results summarized
in Table 3 indicate, di-, tri-, and even tetrasubstituted
alkenyl iodides can be successfully employed. In all
cases, both the starting alkenyl iodides and the products
were g98% stereoisomerically pure. In the absence of
chemoselectivity problems, HCtCMgBr appears to be
almost as satisfactory as HCtCZnBr, although the
superior reactivity of the latter is seen in the reaction of
(E)-4-iodo-5-methyl-4-octene. At least in one case, a
successful use of HCtCSnBu3 for the enyne synthesis
was demonstrated. Once again, however, there does not
appear to be any need or incentive for the reagent.
In conclusion, direct synthesis of terminal alkynes
without protection-deprotection can be achieved by the
Pd-catalyzed coupling of aryl or alkenyl iodides with
ethynylmetals containing Mg, Zn, or Sn. The reaction
of HCtCSnBu3 is generally slower and lower yielding
in some difficult cases. It is further handicapped by its
higher cost and cumbersome isolation and purification
procedures. In cases where no significant difficulties
exist, the use of commercially available HCtCMgBr
should be considered because of its commercial avail-
ability, relative low cost, and operational simplicity. In
more demanding cases, where HCtCMgBr is unsatisfac-
tory as exemplified above, the use of HCtCZnBr can
provide some distinct advantages over that of HCtCMgBr.
The reaction conditions for the other cases are shown in Table
2.
4-Eth yn yltolu en e:15 1H NMR (CDCl3, Me4Si) δ 2.36 (s, 3 H),
3.04 (s, 1 H), 7.13 (d, J ) 8 Hz, 2 H), 7.40 (d, J ) 8 Hz, 2 H)
ppm; 13C NMR (CDCl3, Me4Si) δ 21.49, 76.44, 83.83, 118.99,
129.05, 132.00, 138.94 ppm.
1-Eth yn yl-4-flu or oben zen e:15 1H NMR (CDCl3, Me4Si) δ
3.04 (s, 1 H), 6.9-7.1 (m, 2 H), 7.4-7.6 (m, 2 H) ppm; 13C NMR
(9) Coulson, D. R. Inorg. Synth. 1972, 13, 121.
(10) J enkins, J . M.; Verkade, J . G. Inorg. Synth. 1968, 11, 108.
(11) (a) Sih, C. J .; Salomon, R. G.; Price, P.; Sood, R.; Peruzzotti, G.
J . Am. Chem. Soc. 1975, 97, 857. (b) Zweifel, G.; Miller, J . A. Org.
React. 1984, 32, 375.
(12) Swanson, D. R.; Nguyen, T.; Noda, Y.; Negishi, E. J . Org. Chem.
1991, 56, 2590.
(13) Negishi, E.; Van Horn, D. E.; Yoshida, T. J . Am. Chem. Soc.
1985, 107, 6639.
(14) Apeloig, Y.; Franke, W.; Rappoport, Z.; Schwarz, H.; Stahl, D.
J . Am. Chem. Soc. 1981, 103, 2770.
Exp er im en ta l Section
Gen er a l P r oced u r es. Manipulations involving organome-
tallics were carried out under a dry Ar atmosphere. 1H and 13C
NMR spectra were recorded in CDCl3. NMR yields were
determined by using dibromomethane or mesitylene as an
internal reference. GLC analysis was performed with a column
packed with SE-30 Chromosorb W using a TC detector. All
chemicals obtained from commercial sources were used as
received unless otherwise mentioned. THF was distilled from
(15) Mesmard, D.; Bernadou, F.; Miginiac, L. J . Chem. Res. (M)
1981, 3210.

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Notes
J . Org. Chem., Vol. 62, No. 25, 1997 8959
Ta ble 2. Cr itica l Com p a r ison of Mg, Zn , a n d Sn in th e P d -Ca ta lyzed Cr oss Cou p lin g of Ar yl Iod id es w ith
Eth yn ylm etla lsa
a
b
1.5 equiv of HCtCMgBr relative to ArI was used in each case. By NMR or GLC. The numbers in parentheses are isolated yields.
c Not determined or detected. Generated in situ from HCtCMgBr and dry ZnBr2. e Generated in situ from HCtCMgBr and ClSn(Bu-
d
n)3. f 3 equiv of DMF relative to ArI was added.
(CDCl3, Me4Si) δ 76.93, 82.56, 115.59 (d, J ) 89 Hz), 118.13 (d,
J ) 13 Hz), 134.03 (d, J ) 34 Hz), 162.73 (d, J ) 995 Hz) ppm.
H), 6.81 (s, 2 H) ppm; 13C NMR (CDCl3, Me4Si) δ 20.79, 21.20,
81.35, 84.48, 118.96, 127.51, 137.97, 140.71 ppm.
4-Eth yn yl-1-n itr oben zen e:16 in this case, the reaction tem-
perature was 0 °C; 1H NMR (CDCl3, Me4Si) δ 3.36 (s, 1 H), 7.63
(d, J ) 8.9 Hz, 2 H), 8.19 (d, J ) 8.9 Hz, 2 H) ppm; 13C NMR
(CDCl3, Me4Si) δ 81.56, 82.32, 123.53, 128.87, 132.93, 147.49
ppm.
Meth yl 4-eth yn ylben zoa te:17 1H NMR (CDCl3, Me4Si) δ 3.23
(s, 1 H), 3.89 (s, 3 H), 7.52 (d, J ) 8.5 Hz, 2 H), 7.97 (d, J ) 8.5
Hz, 2 H) ppm; 13C NMR (CDCl3, Me4Si) δ 52.18, 80.04, 82.70,
126.64, 129.35, 130.01, 131.97, 166.27 ppm.
2-Eth yn yla n isole:18 1H NMR (CDCl3, Me4Si) δ 3.31 (s, 1 H),
3.85 (s, 3 H), 6.8-7.0 (m, 2 H), 7.2-7.5 (m, 2 H) ppm; 13C NMR
(CDCl3, Me4Si) δ 55.50, 79.95, 81.03, 110.40, 110.94, 120.22,
130.10, 133.93, 160.36 ppm.
Mesityla cetylen e:19 the reactions were carried out at 60 °C
in DMF or THF with 3 equiv of DMF relative to iodomesitylene;
1H NMR (CDCl3, Me4Si) δ 2.23 (s, 3 H), 2.39 (s, 6 H), 3.40 (s, 1
P d -Ca ta lyzed Cr oss Cou p lin g of Alk en yl Iod id es w ith
Eth yn ylm eta ls. (a ) Rea ction of (E)-4-Iod o-4-octen e w ith
Eth yn ylm a gn esiu m Br om id e. Rep r esen ta tive P r oced u r e
for th e Use of Eth yn ylm a gn esiu m Br om id e. To a flame-
dried 50-mL flask equipped with a magnetic stirring bar were
sequentially added under an Ar atmosphere THF (10 mL), (E)-
4-iodo-octene (1.19 g, 5 mmol), Pd(PPh3)4 (285 mg, 0.25 mmol),
and HCtCMgBr (7.5 mmol, 15 mL of a 0.5 M solution in THF).
Gas chromatographic analysis indicated that the reaction was
complete in 1 h at 22 °C. The reaction mixture was quenched
with aqueous NH4Cl, extracted with pentane, dried over MgSO4,
and concentrated in vacuo. 1H NMR analysis revealed that (E)-
3-(n-propyl)-3-hepten-1-yne was formed in 95% yield. Bulb-to-
bulb distillation afforded this product (0.60 g, 89%) as a colorless
oil: 1H NMR (CDCl3, Me4Si) δ 0.91 (t, J ) 7.6 Hz, 6 H), 1.3-1.7
(m, 4 H), 2.0-2.2 (m, 4 H), 2.73 (s, 1 H), 5.96 (t, J ) 7.6 Hz, 1
H) ppm; 13C NMR (CDCl3, Me4Si) δ 13.56, 13.75, 21.40, 23.37,
30.23, 32.37, 73.68, 85.99, 122.05, 139.73 ppm; IR (neat) 3280,
2116, 1636 cm-1; HRMS calcd for C10H16 (M+) 136.1252, found
136.1249. (b) Rea ction of (E)-4-Iod o-4-octen e w ith Eth y-
n ylzin c Br om id e. This reaction was carried out in the same
manner as above except that HCtCZnBr was used. A solution
of HCtCZnBr was prepared by the reaction of HCtCMgBr and
(16) Gilbert, J . C.; Weerasooriya, U. J . Org. Chem. 1982, 47, 1837.
(17) Austin, W. B.; Bilow, N.; Kelleghan, W. J .; Lau, K. S. Y. J . Org.
Chem. 1981, 46, 2280.
(18) Padwa, A.; Krumpe, K.; Weingarten, M. J . Org. Chem. 1995,
60, 5595.
(19) Rosenberg, D.; Drenth, W. Tetrahedron 1971, 27, 3893.

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8960 J . Org. Chem., Vol. 62, No. 25, 1997
Additions and Corrections
yield: 1H NMR (CDCl3, Me4Si) δ 0.88 (t, J ) 6.8 Hz, 3 H), 1.2-
1.5 (m, 8 H), 2.0-2.2 (m, 2 H), 2.76 (d, J ) 2.2 Hz, 1 H), 5.4-5.6
(m, 1 H), 6.2-6.4 (m, 1 H) ppm; 13C NMR (CDCl3, Me4Si) δ 14.10,
22.63, 28.57, 28.82, 31.69, 33.08, 75.55, 82.61, 108.49, 146.96
ppm; IR (neat) 3312, 2186, 1654 cm-1; HRMS calcd for C10H16
(M+) 136.1252, found 136.1253.
Ta ble 3. Dir ect Syn th esis of 3-En -1-yn e via
P d -Ca ta lyzed Cou p lin g of Alk en yl Iod id es w ith
Eth yn ylm eta ls Con ta in in g Mg a n d Zn a
The reaction conditions for the other cases are shown in Table
3.
(E)-4-Meth yl-3-d ecen -1-yn e: 1H NMR (CDCl3, Me4Si) δ 0.88
(t, J ) 6.2 Hz, 3 H), 1.2-1.5 (m, 8 H), 1.89 (s, 3 H), 2.07 (t, J )
7.0 Hz, 2 H), 2.99 (d, J ) 2.2 Hz, 1 H), 5.2-5.3 (m, 1 H) ppm;
13C NMR (CDCl3, MeSi4) δ 14.02, 19.14, 22.55, 27.45, 28.85,
31.65, 38.59, 79.26, 81.82, 103.55, 154.53 ppm; IR (neat) 3314,
2100, 1654 cm-1; HRMS calcd for C11H18 (M+) 150.1408, found
150.1405.
(E)-4-Meth yl-3-(n -pr opyl)-3-h epten -1-yn e: 1H NMR (CDCl3,
Me4Si) δ 0.90 (t, J ) 6.2 Hz, 6 H), 1.3-1.6 (m, 3 H), 1.94 (s, 3
H), 2.0-2.2 (m, 4 H), 3.02 (s, 1 H) ppm: 13C NMR (CDCl3, Me4-
Si) δ 13.73, 14.02, 21.25, 21.35, 21.94, 33.56, 35.53, 79.12, 84.76,
116.77, 145.44 ppm; IR (neat) 3314, 2088, 1684 cm-1; HRMS
calcd for C11H18 (M+) 150.1408, found 150.1405.
Ack n ow led gm en t. We thank the National Insti-
tutes of Health (GM 36792) for support of this research.
We also thank J ohnson Matthey for a load of palladium
compounds.
Su p p or tin g In for m a tion Ava ila ble: 1H and 13C NMR
spectra of three iodoalkenes, i.e., (E)-4-iodo-4-octene, (E)-1-iodo-
2-methyl-1-octene, and (E)-4-iodo-5-methyl-4-octene, their ethy-
nylated derivatives, and six phenylethyne derivatives contain-
ing 2,5-dimethyl, p-F, p-NO2, p-COOMe, o-MeO, and 2,4,6-
trimethyl groups (24 pages). This material is contained in
libraries on microfiche, immediately follows this article, and
can be ordered from the ACS; see any current masthead page
for ordering information.
a
b
1.5 equiv of MCtCH was used. NMR yield. The stereoiso-
meric purity in each case was g98%. c Generated in situ from
d
HCtCMgBr and dry ZnBr2. Generated in situ from HCtCMgBr
and ClSnBu3. e 5 mol % of Cl2Pd(PPh3)2 was used.
dry ZnBr2 in THF. 1H NMR analysis indicated the formation
of (E)-3-(n-propyl)-3-hepten-1-yne in 96% yield. (c) Rea ction
of (E)-1-iod o-1-octen e w ith Eth yn yltr ibu tyltin . This reac-
tion was carried out in the same manner as above except that
HCtCSn(Bu-n)3 was used and reaction time was 6 h. 1H NMR
analysis indicated the formation of (E)-3-decen-1-yne in 95%
J O971552B
Additions and Corrections
Vol. 62, 1997
(2) Dondoni, A.; Fantin, G.; Fogagnolo, M.; Pedrini, O.
J . Org. Chem. 1990, 55, 1439.
W. E. Acr ee, J r .,* J oyce R. P ow ell, Sh er yl A. Tu ck er ,
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Page 3724, Table 3. The last four column headings
should read as follows: -∆cH0m(cr), ∆fH0m(cr), ∆cgrHm0 ,
and ∆fH0m(g).
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J O974016S
J O974021W
Leo A. P a qu ette,* Th om a s M. Mitzel, Meth vin B. Isa a c,
Cu r tis F . Cr a sto, a n d Willia m W. Sch om er . Diastereoselec-
tion during 1,2-Addition of the Allylindium Reagent to R-Thia
and R-Amino Aldehydes in Aqueous and Organic Solvents.
Ser gey P . Ver evk in , Ma r got No1lk e, Ha n s-Dieter
Beck h a u s, a n d Ch r istop h Ru1 ch a r d t*. Enthalpies of Forma-
tion of Hexaethylethane, Octamethylhexane, and Tri-tert-butyl-
methane. Extremely Strained Hydrocarbons.
Page 4293. The elegant studies by Duhamel and by
Dondoni on a tunable stereoselectivity of organometallic
additions to variously protected R-amino aldehydes were
inadvertently not acknowledged. The relevant references
are as follows:
Page 4684. In the Discussion the following numbers
should be corrected: line 9, Hs ) 177.2 kJ ‚mol-1; line 10,
Hs ) 156.1 kJ ‚mol-1; line 11 Hs ) 118.1 kJ ‚mol-1. The
strain enthalpies Hs are correctly recorded in Table 1.
(1) Duhamel, P.; Duhamel, L.; Gralak, J . Tetrahedron
Lett. 1972, 2329.
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