The Preparation and Reactivity of 2-Bromo-3-(tri- n -butylstannyl)-1-propene

Article abstract of DOI:10.1055/s-0036-1588883

The preparation of 2-bromo-3-(tri-n-butylstannyl)-1-propene is described. This study characterizes the reactivity of 2-bromo-3-(tri-n-butylstannyl)-1-propene in S_E′ reactions with aldehydes and includes a survey of radical reactions of 2-bromo-3-(tri-n-butylstannyl)-1-propene with α-bromocarbonyl compounds for C-alkylation.

Full text of DOI:10.1055/s-0036-1588883

SYNLETT
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© Georg Thieme Verlag Stuttgart · New York
2016, 27, A–E
letter
A
D. R. Williams et al.
Letter
Synlett
The Preparation and Reactivity of 2-Bromo-3-(tri-n-butylstannyl)-
1-propene
SE' reaction
David R. Williams*
Akshay A. Shah1
Dawn A. Brooks2
Nicolas Zorn3
HO
CHO
TBDPSO
TBDPSO
Br
OPMB
SnBu3
OPMB
BF3•OEt2, CH2Cl2
Br
Department of Chemistry, Indiana University, Bloomington,
IN 47405, USA
williamd@indiana.edu
O
N
radical reaction
Br
O
Br
N
AIBN, toluene
Received: 13.05.2016
Accepted after revision: 25.08.2016
Published online: 09.09.2016
account of their study includes characterization data.10 Sub-
sequently, studies in our laboratories have explored the use
of the nonracemic stien controllers in asymmetric SE′ pro-
cesses,11 and we have also extended this methodology for
total synthesis.12 Our investigations have utilized 2-bromo-
3-(tri-n-butylstannyl)-1-propene (1),13 and as a basis for
preparation of 1, we have adapted the general information
found in footnote 8 of the original communication (see ref.
9a). We have frequently received requests for a detailed ex-
perimental procedure for the preparation and handling of
2-bromo-3-(tri-n-butylstannyl)-1-propene (1). In this com-
munication, we have summarized the reactivity of 1 in SE′
reactions with aldehydes to effect stereocontrolled forma-
tion of homoallylic alcohols, and we have reported new re-
sults of a survey of the radical reactions of 1 with α-bromo-
carbonyl compounds. Most significantly, this communica-
tion provides detailed experimental descriptions for two
procedures leading to the preparation, the characterization,
and the handling of this reactive reagent.
Bifunctional reagent 1 is exceptionally reactive in SE′
substitution processes in which electrophilic attack leads to
destannylation with allylic transposition. It is well-known
that aldehydes efficiently undergo these reactions at –78 °C
in the presence of a Lewis acid catalyst as shown in Scheme
1. Four examples are highlighted from our prior efforts to
illustrate typical conditions leading to stereocontrolled re-
actions using stannane 1. Homoallylic alcohols are pro-
duced as exemplified by the formation of 3 from the chiral
nonracemic aldehyde 2. In this example, the use of BF3·OEt2
results in the diastereoselective synthesis of 3 as predicted
by the polar Felkin–Anh model. Substrate-controlled reac-
tions are also demonstrated by the precomplexation of the
α-alkoxyaldehyde 2 with a divalent cation. This reaction
provides efficient formation of the syn-alcohol 4 with high
diastereoselectivity arising from a chelation-controlled ad-
dition (Scheme 1, eq. 2).13a
DOI: 10.1055/s-0036-1588883; Art ID: st-2016-r0340-l
Abstract The preparation of 2-bromo-3-(tri-n-butylstannyl)-1-pro-
pene is described. This study characterizes the reactivity of 2-bromo-3-
(tri-n-butylstannyl)-1-propene in SE′ reactions with aldehydes and in-
cludes a survey of radical reactions of 2-bromo-3-(tri-n-butylstannyl)-1-
propene with α-bromocarbonyl compounds for C-alkylation.
Key words organostannane preparation, bifunctional reagent, SE′ re-
actions, radical reaction, alkenyl bromides
Our studies of natural product synthesis have sought
improved strategies for the efficient assembly of molecular
complexity by utilizing bifunctional reagents that provide
for the sequential execution of high-value reactions.4 In
fact, the design of efficient strategies for total synthesis has
provided an important impetus for the creative deployment
of bifunctional synthons.5 We have examined a sequential
linkage of asymmetric SE′ reactions and cross-coupling pro-
cesses to present a versatile strategy for the preparation of
complex enantioenriched alcohols.6,7 In this fashion, bi-
functional reagents serve as lynchpins in tandem applica-
tions of orthogonal reaction processes. Several contribu-
tions have explored this theme, as practitioners have exten-
sively developed a variety of bifunctional allyl synthons to
facilitate convergent synthesis pathways.8 This concept
avoids a stepwise construction and the use of protecting
groups. In 1989, Corey and co-workers first introduced a
protocol for the enantioselective allylation of aldehydes us-
ing the 1,2-diamino-1,2-diphenylethane (stien) controller.9
This initial publication is the first report of 2-bromo-3-tri-
n-butylstannyl-1-propene (1, 2-bromoallyltri-n-butyltin)
in the literature and its use in asymmetric SE′ reactions. Pu-
lido and co-workers have also described the formation of 1
by a kinetic stannylcupration of allene at –100 °C, and a full
© Georg Thieme Verlag Stuttgart · New York — Synlett 2016, 27, A–E

B
D. R. Williams et al.
Letter
Synlett
The allylic stannane of 1 also broadly promotes trans-
metalation. This reactivity is the basis for the exchange of
the stannyl residue with boron leading to in situ formation
of chiral, nonracemic 1,3-bis(tolylsulfonyl)-4,5-diphenyl-
1,3-diaza-2-borolidines. As a result, reagent-controlled
asymmetric allylation reactions of 1 with simple aldehydes
readily occur at –78 °C. In these cases, the reactive stannane
undergoes transmetalation with the chiral, nonracemic
bromoborane 6. As illustrated in Scheme 1, eq. 3, subse-
quent addition of aldehyde 5 leads to the enantioenriched
alcohol 7. Reactions of the nonracemic 1,3-diaza-2-boroli-
dine intermediate 9 with chiral aldehydes, such as 8 in
Scheme 1, eq. 4, can lead to interesting matched and mis-
matched stereochemical features favoring transition state
10 and produces excellent diastereoselectivity as illustrated
with the formation of 11.13b This methodology is robust and
has proven to be useful for convergent strategies which
stitch together complex molecular subunits containing sig-
nificant functionality and stereochemistry.14
Example 1
1
SnBu3
BF3•OEt2
O
Br
OH
TBDPSO
H
(1)
H
CH2Cl2, –78 °C
TBDPSO
TBDPSO
Br
Br
OPMB
H
OPMB
2
3 (anti)
[84%; dr 12:1]
Example 2
SnBu
Br
MgBr2•OEt2 (1.1 equiv)
3 1
O
OH
TBDPSO
H
(2)
H
CH2Cl2, –78 °C
H
OPMB
OPMB
2
4 (syn)
80% [dr 20:1]
Example 3
Br
Br
OH
O
1
SnBu3
Ts
N
N
O
O
H
O
N
(3)
O
N
Ph
Ph
N
CH3
CH3
6
B
Br
7
5
N
88% [er 91:9]
Ts
CH2Cl2, 0 °C → r.t.;
then add 5 at –78 °C
Example 4
Ts
1
SnBu3
Ts
Ph
Ph
Br
N
B
N
(4)
CHO
Br
TBDPSO
Ph
R
N
8
Ts
6
B
Br
N
R
9
Ph
Ts
CH2Cl2, 22 °C;
then add aldehyde 8 at –78 °C
Tol
O
δ+
H
O
S
O
OH
H
δ–
R
N
B
TBDPSO
H
Ph
H
H
N
H
Br
SitBuPh2
O
Br
Ph
O
S
11
85% [dr 99:1]
10
O
Tol
Scheme 1 Examples of SE′ reactions of 1 with aldehydes
© Georg Thieme Verlag Stuttgart · New York — Synlett 2016, 27, A–E

C
D. R. Williams et al.
Letter
Synlett
Our initial studies of 2-bromo-3-(tri-butylstannyl)-1-
propene (1) have characterized its radical-mediated reac-
tions with a variety of organic halides to incorporate an
alkenyl bromide moiety in C–C bond formation. These find-
ings are presented in Table 1. In this survey, α-bromo car-
bonyl compounds are preferred substrates. Reactions are
conducted in dry toluene under nitrogen atmosphere with
gradual heating from 22 °C to 85 °C in the presence of the
stannane reagent 1 (2.5–3.5 equiv) and small amounts of
AIBN initiator. Generally, α-bromoamides, esters, and ke-
tones are effectively consumed with the formation of alke-
nyl bromide products (Table 1, entries 1–5) in yields of 61–
73%. The corresponding reactions of α-iodo ketones and es-
ters proceed in poor yields, and aryl iodides and bromides
are unreactive. Limited studies have probed the use of pri-
mary alkyl bromides and iodides and lead to slow reactions
with 1 generating modest yields of the desired alkenyl bro-
mides 22 and 24 (Table 1, entries 6 and 7). The rate of the
thermal decomposition of stannane 1 becomes a significant
factor in these later examples and requires the introduction
of an additional aliquot of reagent. With the consumption
of 4.5 equivalents of 1, the products 22 and 24 were pro-
duced in yields of 50% and 41%, respectively with the recov-
ery of 15% of the starting halides after three hours at 90 °C.
Secondary and tertiary halides did not provide useful yields
of the expected products.
Table 1 Radical Reactions of Reagent 1 with Reactive Halidesa
Entry Starting halide
Product (Yield)b
Yield (%)b
73%
O
O
Br
N
N
1
Br
11
12
O
O
2
O
61%
71%
68%
64%
Br
Br
O
13
Br
Br
14
O
O
3
16
15
O
O
Br
4
5
EtO
EtO
Br
Br
17
18
O
O
Br
O
EtO
EtO
EtO
EtO
O
The formation of the desired 2-bromo-3-(tri-n-bu-
tystannyl)-1-propene (1)15 begins with the preparation of a
solution of tributylstannyllithium as described by pub-
lished procedures.16 To a flame-dried flask containing dis-
tilled diisopropylamine (12.0 mL, 85.1 mmol) at 0 °C under
inert atmosphere, n-butyllithium (2.5 M in hexanes, 31.7
mL; 79.0 mmol) is added dropwise with stirring. Lithium
diisopropylamide is formed as a white precipitate, and vol-
atile hexanes and excess amine are then removed in vacuo.
Anhydrous THF (143 mL) is then carefully introduced as the
reaction flask is maintained at 0 °C under argon. Tri-n-bu-
tylstannane (21.3 mL, 79.0 mmol) is added dropwise via sy-
ringe, and the mixture is stirred for an additional 40 min at
0 °C. The reaction mixture is subsequently cooled to –78 °C,
and pre-dried CuBr·DMS (16.25 g, 79.0 mmol) is quickly
added as a solid in one portion. During this process, the re-
action flask is wrapped with aluminum foil to protect the
contents from light, and the reaction mixture becomes an
opaque greenish brown in color. This mixture is stirred un-
der argon and protected from light for 2 h at –78 °C. Subse-
quently, a solution of the methanesulfonate (13.0 g, 60.7
mmol), derived from 2-bromo-1-propen-3-ol,17 in 20 mL of
dry THF is introduced by dropwise addition at –78 °C, and
the reaction is allowed to warm to 0 °C with further stirring
for 3 h at 0 °C. TLC (20% EtOAc in hexanes) indicates the dis-
appearance of starting mesylate and the formation of de-
sired product (Rf = 0.75). The reaction is quenched by the
addition of pH 7 buffer (200 mL), and this mixture is fil-
19
21
20
22
H
H
H
O
Br
O
O
50%c
41%c
O
6
7
H
H
H
Br
O
I
O
23
Br
24
a Stannane 1, prepared as described, was introduced by syringe as a neat liq-
uid (220 mg, 3.1 equiv, based on 80% purity of 1 from 1H NMR analysis) into
a 1 M solution of aldehyde (0.14 mmol) in dry toluene. Several crystals of
AIBN were added, and reactions were gradually heated to 85 °C under N2.
b Products were purified by flash silica gel chromatography and were charac-
terized by 1H NMR and 13C NMR analysis. Yields are based on isolated prod-
ucts.
c Yields of 22 and 24 were 62% brsm and 52% brsm as starting aldehyde
(15%) was recovered in these examples.
tered through a Buchner funnel using small amounts of
pentane. The filtrate is separated into two phases in a sepa-
ratory funnel and the aqueous layer is washed with pen-
tane (3 × 150 mL). The combined organic phases are dried
over anhydrous Na2SO4 and neutralized charcoal, and then
filtered through a pad of Celite®. The resulting colorless
solution is protected from light and concentrated under re-
duced pressure while maintaining the bath temperature at
approximately 20 °C. Further removal of small amounts of
© Georg Thieme Verlag Stuttgart · New York — Synlett 2016, 27, A–E

D
D. R. Williams et al.
Letter
Synlett
solvents under high vacuum gave a colorless to slightly yel-
low oil. The crude product represents 80–89% of the theo-
retical mass recovery. This material is evaluated by 1H NMR
and 13C NMR analysis to assess its purity. 1H NMR spectros-
copy shows signals for two vinylic hydrogens (δ = 5.25 and
5.00 ppm) as well as the allylic methylene of 1 (δ = 2.32
ppm, Figure 1). Evidence for the presence of small amounts
(4% or less) of n-Bu3SnH is based upon the characteristic 1H
NMR signal (δ = 4.64 (Sn–H) ppm). The major impurity has
been identified as hexabutylditin (Bu3SnSnBu3),18 which is
estimated as 10–15% of the crude product using GC–HRMS
with chemical ionization employing isobutane. Unfortu-
nately, both low-resolution MS and various HRMS tech-
niques have failed to provide the confirming identification
of a molecular ion signal for 1. Mass fragments of tri-n-bu-
tylstannyl and tri-n-butyltin bromide are observed. Using
the relative integration of vinylic, allylic, and tri-n-butyl
under an argon atmosphere. A solution of anhydrous THF
(20.0 mL) containing several crystals of naphthalene is de-
gassed three times with argon and then is transferred via
cannula for reaction with the lithium pieces to give a dark
green solution. Hexabutylditin (7.52 mL, 15.0 mmol) is
added dropwise via syringe, and the resulting mixture is
heated to 50 °C overnight (10 h). Upon cooling to r.t., the
dark brown solution is transferred via a Schlenk filtration
through a pad of dry Celite® into a flask containing a sus-
pension of recrystallized CuBr·DMS (6.16 g, 30.0 mmol) in
anhydrous THF (30.0 mL) at –78 °C. The mixture is protect-
ed from light and is continuously stirred at –78 °C for an ad-
ditional two hours, becoming an opaque greenish-brown
color. Freshly distilled 2,3-dibromopropene (3.88 mL, 30.0
mmol) is added via syringe, and the mixture is allowed to
warm to 0 °C over 3 h. The reaction is quenched by addition
of pH 7 buffer (100 mL) and the organic layer is separated.
The aqueous phase is extracted with pentane (200 mL × 3),
and the combined organic phases are washed with sat. aq
NaCl (300 mL × 2). The resulting pentane solution is dried
over MgSO4 and decolorized by the addition of neutral acti-
vated charcoal, followed by filtration through a column of
basified silica gel (250 mL volume) with the aid of a small
amount of pentane. The filtrate is concentrated in vacuo to
afford the stannane 1 (6.95 g, 17.1 mmol, 57%) as a pale yel-
low oil. The quality of the crude product 1 is generally com-
parable to material prepared from the mesylate. However,
in practice, we have preferred the use of the mesylate
method, in spite of the additional steps required for prepa-
ration of the starting alcohol and its sulfonate. Hexabutyldi-
tin is the major impurity in these samples (approximately
15%). For the characterization of stannane 1: Rf = 0.75 (SiO2,
20% EtOAc in hexanes). 1H NMR (400 MHz, CDCl3): δ = 5.25
(1 H, d, J = 1.1 Hz), 5.00 (1 H, d, J = 1.1 Hz), 2.32 (2 H, br s),
1.60–1.44 (6 H, m), 1.37–1.25 (6 H, m), 0.98 (6 H, t, J = 8.0
Hz), 0.90 (6 H, t, J = 8.0 Hz) (Sn satellites are not reported).
13C NMR (101 MHz, benzene-d6): δ = 135.4, 111.2, 29.5,
27.8, 26.7, 14.0, 10.2.
1
signals in the H NMR data, the estimated purity of crude
reaction product is determined to be 80–85% of the desired
2-bromo-3-(tri-n-butylstannyl)-1-propene (1), based on
the presence of hexabutyl ditin. Thus, the calculated yield
of 1 is 65–70%, and this material is used directly for subse-
quent reactions. Yields deteriorate without the use of high
quality CuBr·DMS and freshly distilled tri-n-butylstannane.
Small amounts of the crude product have been distilled by
the Kugelrohr bulb-to-bulb transfer technique (oven tem-
perature of 68–72 °C at 1.2 mmHg pressure). However, the
colorless distillate is evaluated as desired 1 (approximately
85% pure) containing small quantities of unknown impuri-
ties which appear as a result of the distillation (see Sup-
porting Information).
Stock solutions of reagent 1 are prepared in dry CH2Cl2
or toluene, and aliquots of these solutions are directly uti-
lized based upon the percent weight of 1. Dichloromethane
solutions of 2-bromo-3-(tri-n-butylstannyl)-1-propene are
stored in the freezer (–20 °C) under argon for one week
without signs of deterioration. However, samples stored at
0 °C showed increasing intensity of a singlet in the 1H NMR
spectrum which indicates the formation of allene (δ = 4.68
ppm). Our preparation of stannane 1 provides a thermally
labile product which undergoes an accelerating rate of de-
composition upon standing at 22 °C overnight. The reagent
1 is generally unstable in the presence of aqueous acids and
suffers decomposition on attempts for standard silica gel
flash chromatography. The use of deactivated or basified
silica gel fails to improve the overall purity of the sample.
The presence of hexabutylditin does not adversely affect SE′
reactions of 1 with aldehydes as described in Scheme 1, eq.
Figure 1 1H NMR spectrum of 1 for the region δ = 2.0–5.5 ppm illus-
trates vinylic and allylic hydrogen signal patterns, including observed
Sn satellites
Our studies for the preparation of 1 have also examined
a second method which utilizes hexabutylditin and com-
mercially available 2,3-dibromopropene while avoiding the
use of tri-n-butylstannane. For this procedure, lithium wire
(1.04 g, 150.0 mmol) is pressed into a thin strip, cut into
small pieces under mineral oil, and added into a flame-
dried flask, equipped with a stirring bar and a condenser,
© Georg Thieme Verlag Stuttgart · New York — Synlett 2016, 27, A–E

E
D. R. Williams et al.
Letter
Synlett
1–4. However, we assume that stannylated impurities may
suppress optimal yields of the radical-based reactions of Ta-
ble 1.
Soc. 2009, 131, 1269. (h) Binanzer, M.; Fang, G. Y.; Aggarwal, V.
K. Angew. Chem. Int. Ed. 2010, 49, 4264. (i) Nishiyama, H.;
Narimatsu, S.; Itoh, K. Tetrahedron Lett. 1981, 22, 5289.
(9) (a) Corey, E. J.; Yu, C.-M.; Kim, S.-S. J. Am. Chem. Soc. 1989, 111,
5495. (b) Corey, E. J.; Kim, S.-S. Tetrahedron Lett. 1990, 31, 3715.
(10) (a) Barbero, A.; Cuadrado, P.; Fleming, I.; González, A. M.;
Pulido, F. J. Chem. Commun. 1990, 1030. (b) Barbero, A.;
Cuadrado, P.; Fleming, I.; González, A. M.; Pulido, F. J. J. Chem.
Soc., Perkin Trans. 1 1992, 327. (c) The data for the product 2-
bromo-3-(tributylstannyl)prop-1-ene is given as follows: 1H
NMR (400 MHz, CDCl3): δ = 5.6 (1 H, m), 5.35 (1 H, m), 2.25 (2 H,
s), 1.70–0.70 (27 H, m). The reported data of their product
differs substantially with respect to the key vinylic and allylic
hydrogen assignments of Figure 1.
(11) (a) Williams, D. R.; Brooks, D. A.; Meyer, K. G.; Clark, M. P. Tetra-
hedron Lett. 1998, 39, 7251. (b) Williams, D. R.; Meyer, K. G.;
Shamim, K.; Patnaik, S. Can. J. Chem. 2004, 82, 120.
(12) For examples, see: (a) Williams, D. R.; Kiryanov, A. A.; Emde, U.;
Clark, M. P.; Berliner, M. A.; Reeves, J. T. Proc. Natl. Acad. Sci.
U.S.A. 2004, 101, 12058. (b) Williams, D. R.; Plummer, S. V.;
Patnaik, S. Org. Lett. 2003, 5, 5035. (c) Williams, D. R.; Brooks, D.
A.; Berliner, M. A. J. Am. Chem. Soc. 1999, 121, 4924.
In summary, a detailed experimental procedure reports
the preparation of 2-bromo-3-(tri-n-butylstannyl)-1-pro-
pene, including spectroscopic characterization data. The in-
stability of this reagent and major impurities have been de-
1
scribed using HRMS and H NMR sample analysis. This bi-
functional reagent undergoes C–C bond-forming radical
reactions with α-bromocarbonyl compounds and demon-
strates excellent reactivity at –78 °C in SE′ processes with al-
dehydes. Stannane 1 should prove generally useful in a vari-
ety of mild transmetalation reactions.
Acknowledgment
This material is based upon work supported by the National Science
Foundation under Grant No. CHE-1362561.
(13) (a) Williams, D. R.; Walsh, M. J.; Claeboe, C. D.; Zorn, N. Pure
Appl. Chem. 2009, 81, 181. (b) Williams, D. R.; Atwater, B. A.;
Bawel, S. A.; Ke, P.; Gutierrez, O.; Tantillo, D. J. Org. Lett. 2014,
16, 468.
(14) For a discussion in total synthesis: Williams, D. R.; Plummer, S.
V.; Patnaik, S. Tetrahedron 2011, 67, 5083.
Supporting Information
Supporting information for this article is available online at
http://dx.doi.org/10.1055/s-0036-1588883.
S
u
p
p
ortioInfgrmoaitn
S
u
p
p
ortiInfogrmoaitn
(15) For preparation of the corresponding 2-chloro-3-(tri-n-butyl-
stannyl)-1-propene: Baldwin, J. E.; Adlington, R. M.; Lowe, C.;
O’Neil, I. A.; Sanders, G. L.; Schofield, C. J.; Sweeney, J. B. Chem.
Commun. 1988, 1030.
References and Notes
(1) New address: A. A. Shah, Pfizer, Groton, CT, 06340, USA.
(2) New address: D. A. Brooks, Eli Lilly & Company, Indianapolis, IN
46285, USA.
(16) Still, W. C. J. Am. Chem. Soc. 1978, 100, 1481.
(17) The allylic alcohol 2-bromo-1-propen-3-ol (10.6 g, 64.3 mmol)
was dissolved in CH2Cl2 at 0 °C, and Et3N (10.3 mL, 73.9 mmol)
was added under inert atmosphere. After stirring for 5 min,
methanesulfonyl chloride (5.72 mL, 73.9 mL) was added drop-
wise at 0 °C. The reaction mixture was allowed to warm to 22 °C
with continued stirring over 2 h. TLC (20% EtOAc in hexanes)
shows the production of a less polar mesylate and the disap-
pearance of starting alcohol. The reaction mixture was concen-
trated under reduced pressure to approximately one-third of its
volume, and the concentrate was diluted with Et2O (150 mL).
The mixture was filtered through a pad of Celite® to remove the
triethylammonium hydrochloride precipitate with the aid of
additional quantities of Et2O. The filtrate was concentrated in
vacuo to give the crude mesylate as a yellow oil with yields con-
sistently in the 85–90% range. Vacuum distillation (1.4 mm Hg
pressure) by Kugelrohr bulb-to-bulb transfer at an oven tem-
perature of 60 °C afforded product as a colorless liquid which
was judged to be >97% pure based on the 1H NMR and 13C NMR
spectra of these samples. 1H NMR (400 MHz, CDCl3): δ = 6.08 (1
H), 5.78 (1 H), 4.81 (2 H), 3.09 (3 H). 13C NMR (400 MHz, CDCl3):
δ = 124.1, 121.7, 72.3, 38.5). HRMS (CI): m/z calcd for C4H8BrO3S
[M + H]+ 214.9372; found: 214.9372. This mesylate was directly
utilized in the next step.
(3) New address: N. Zorn, F. Hoffmann-La Roche AG, 4070 Basel,
Switzerland.
(4) (a) For an example of sequential SE′ reactions, see: Williams, D.
R.; Claeboe, C. D.; Liang, B.; Zorn, N.; Chow, N. S. C. Org. Lett.
2012, 14, 3866. (b) For an example of sequential cross coupling–
carbocyclization reactions, see: Williams, D. R.; Shah, A. A.;
Mazumder, S.; Baik, M.-H. Chem. Sci. 2013, 4, 238.
(5) Two illustrative examples of total syntheses are cited: (a) Piers,
E.; Gilbert, M.; Cook, K. L. Org. Lett. 2000, 2, 1407. (b) Martin, D.
B. C.; Vanderwal, C. D. J. Am. Chem. Soc. 2009, 131, 3472.
(6) Williams, D. R.; Meyer, K. G. J. Am. Chem. Soc. 2001, 123, 765.
(7) For related reagents described from our laboratory, see:
(a) Williams, D. R.; Fultz, M. W. J. Am. Chem. Soc. 2005, 127,
14550. (b) Williams, D. R.; Morales-Ramos, Á. I.; Williams, C. M.
Org. Lett. 2006, 8, 4393.
(8) For a representative sampling of reports, featuring bifunctional
allyl synthons, see: (a) Ferris, G. E.; Hong, K.; Roundtree, I. A.;
Morken, J. P. J. Am. Chem. Soc. 2013, 135, 2501. (b) Sieber, J. D.;
Morken, J. P. J. Am. Chem. Soc. 2006, 128, 74. (c) Chen, M.;
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