Lithium-Iodine Exchange Mediated Atom Transfer Cyclization: Catalytic Cycloisomerization of 6-Iodo-1-hexenes

Article abstract of DOI:10.1021/jo971939e

Treatment of 6-iodo-1-hexene (1) in a variety of solvent systems with either MeLi or PhLi at room temperature or above effects clean cycloisomerization of 1 to (iodomethyl)cyclopentane (4). This novel transformation, which is mediated by rapid and reversible lithium-iodine exchange processes, most likely involves the following discrete steps: (i) generation of 5-hexenyllithium (2) from 1 by exchange with MeLi or PhLi, (ii) irreversible cyclization of 2 to give (cyclopentylmethyl)lithium (3) and (iii) virtually complete conversion of 3 to (iodomethyl)cyclopentane (4) via a highly favorable lithium-iodine exchange equilibrium. The isomerization sequence 1 → 4 has been found to be effectively catalytic in PhLi when conducted in hydrocarbon-ether solvent mixtures at room temperature.

Full text of DOI:10.1021/jo971939e

J . Org. Chem. 1998, 63, 361-365
361
Lith iu m -Iod in e Exch a n ge Med ia ted Atom Tr a n sfer Cycliza tion :
Ca ta lytic Cycloisom er iza tion of 6-Iod o-1-h exen es
William F. Bailey* and Matthew W. Carson
Department of Chemistry, The University of Connecticut, Storrs, Connecticut 06269-4060
Received October 21, 1997X
Treatment of 6-iodo-1-hexene (1) in a variety of solvent systems with either MeLi or PhLi at room
temperature or above effects clean cycloisomerization of 1 to (iodomethyl)cyclopentane (4). This
novel transformation, which is mediated by rapid and reversible lithium-iodine exchange processes,
most likely involves the following discrete steps: (i) generation of 5-hexenyllithium (2) from 1 by
exchange with MeLi or PhLi, (ii) irreversible cyclization of 2 to give (cyclopentylmethyl)lithium (3)
and (iii) virtually complete conversion of 3 to (iodomethyl)cyclopentane (4) via a highly favorable
lithium-iodine exchange equilibrium. The isomerization sequence 1 f 4 has been found to be
effectively catalytic in PhLi when conducted in hydrocarbon-ether solvent mixtures at room
temperature.
Low-temperature lithium-iodine exchange between a
primary alkyl iodide and 2 molar equiv of t-BuLi in a
solvent system containing diethyl ether affords the
corresponding primary alkyllithium irreversibly and in
virtually quantitative yield.1 When the exchange is
conducted using a less reactive organolithium, an equi-
librium favoring the more stable organolithium is rapidly
established:2,3 R-I + R′-Li h R-Li + R′-I. It occurred
to us that it might be possible to exploit the reversible
nature of the lithium-iodine exchange reaction to effect
isomerization of an alkyl iodide if the initially generated
alkyllithium were to undergo an irreversible rearrange-
ment prior to reconversion to the iodide. In an effort to
explore this possibility, we have investigated the revers-
ible lithium-iodine exchange reaction of 6-iodo-1-hexene
(1) with relatively unreactive organolithiums to give
5-hexenyllithium (2) under conditions known to result
in irreversible cyclization of 2 to (cyclopentylmethyl)-
lithium (3).4 In principle, as summarized in the scenario
presented below (eqs 1-3), treatment of 1 with an
appropriate RLi should lead to a net isomerization of 1
to (iodomethyl)cyclopentane (4) provided that the orga-
nolithium used to initiate the sequence is sufficiently
stable to ensure that the equilibrium represented in eq
3 lies far to the right. Herein we disclose the first
examples of this anionic atom-transfer isomerization.
MeLi or PhLi to initiate the sequence (eqs 1-3).5 In light
of the fact that the cyclization of 2 to 3 (eq 2) in ethereal
solution is fairly rapid only at temperatures above 0 °C
(t1/2 ≈ 5 min at 22 °C),4,6 reactions were conducted at room
temperature or above using 0.1 M solutions of 1 under a
variety of experimental conditions to survey the effect of
solvent, temperature, and reaction time on the isomer-
ization (Table 1). Initial experiments (Table 1, entries
1-8) employed a full molar equivalent of the organo-
lithium initiator due to concern that, at the elevated
temperatures needed to effect cyclization of 2 to 3, such
side reactions as coupling, elimination, and proton ab-
straction from solvent might consume the reactive orga-
nometallics.3 However, as demonstrated by the results
Resu lts a n d Discu ssion
The potential lithium-iodine exchange mediated
isomerization of 1 f 4 was investigated using either
(5) It is important to note that the more reactive alkyllithiums are
much less effective than MeLi or PhLi for initiation of the isomerization
sequence. Not only is the equilibrium represented in eq 3 less favorable
for the production of 4 when a reactive alkyllithium such as n-BuLi is
employed but, more importantly, the predominant outcome of the
reaction of an alkyllithium with 1 at room temperature is coupling.
Thus, for example, an equimolar solution of 1 and n-BuLi in Et2O is
converted to a mixture of all possible coupling products [octane,
1-decene, pentylcyclopentane, 1,11-dodecadiene, 7-cyclopentyl-1-hep-
tene, and 1,2-dicyclopentylethane] in ∼88% yield on standing at 22
°C for 0.5 h.
X Abstract published in Advance ACS Abstracts, December 15, 1997.
(1) Bailey, W. F.; Punzalan, E. R. J . Org. Chem. 1990, 55, 5404.
(2) Applequist, D. E.; O’Brien, D. F. J . Am. Chem. Soc. 1963, 85,
743.
(3) (a) Wakefield, B. J . The Chemistry of Organolithium Compounds;
Pergamon Press: New York, 1974. (b) Bailey, W. F.; Patricia, J . J . J .
Organomet. Chem. 1988, 352, 1. (c) Gilman, H.; J ones, R. G. Org.
React. (N.Y.) 1951, 6, 339.
(4) Bailey, W. F.; Patricia, J . J .; DelGobbo, V. C.; J arret, R. M.;
Okarma, P. J . J . Org. Chem. 1985, 50, 1999. (b) Bailey, W. F.;
Khanolkar, A. D.; Gavaskar, K.; Ovaska, T. V.; Rossi, K.; Thiel, Y.;
Wiberg, K. B. J . Am. Chem. Soc. 1991, 113, 5720.
(6) It might be noted that the rearrangement of 2 to 3 is significantly
more rapid in the presence of a lithiophilic Lewis base such as TMEDA
4b
or THF.
Thus, for example, the half-time for cyclization of 2 in the
presence of TMEDA is only 6 min at -30 °C.
S0022-3263(97)01939-7 CCC: $15.00 © 1998 American Chemical Society
Published on Web 01/23/1998

362 J . Org. Chem., Vol. 63, No. 2, 1998
Ta ble 1. Rea ction of 6-Iod o-1-h exen e (1) w ith MeLi or P h Lia
Bailey and Carson
a
Unless otherwise indicated, reactions were conducted under an argon atmosphere using approximately 0.1 M solutions of 6-iodo-1-
b
hexene in the appropriate solvent to which 1.1 molar equiv of the indicated RLi was added. Yields were determined by capillary GC
using internal standards and correction for detector response. c Total yield of C12H22 compounds [1,11-dodecadiene, 7-cyclopentyl-1-heptene,
d
and 1,2-dicyclopentylethane] produced in the reaction. TMEDA (1.0 molar equiv) was added to a 0.1 M solution of the iodide in pentane
prior to the addition of MeLi. e The reaction mixture also contained 24% of ethylcyclopentane. f Reaction was conducted using 0.25 molar
equiv of PhLi.
presented below, the isomerization of 6-iodo-1-hexene (1)
to (iodomethyl)cyclopentane (4) may be accomplished
cleanly and in high yield using an essentially catalytic
quantity of PhLi as initiator.
serves to remedy the problem (Table 1, cf. entries 6 and
7). It should be noted in this connection that the
isomerization of 1 to 4 can also be accomplished cleanly
in tert-butyl methyl ether (Table 1, entry 3) as well as in
hydrocarbon solvent containing as little as 2 vol % of
diethyl ether (Table 1, entry 8) or 1 molar equiv of
N,N,N′,N′-tetramethylethylenediamine (Table 1, entry 4).
Not surprisingly, given the fact that the rate of
cyclization of 5-hexenyllithium (2) to (cyclopentylmethyl)-
lithium (3) is a strong function of temperature,4 some
benefit derives from conducting the isomerization of 1
to 4 at higher temperatures (Table 1, cf. entries 1, 2, and
3). The increase in reaction rate, however, is purchased
at the cost of incomplete isomerization: at higher tem-
peratures, proton abstraction from solvent is also ac-
celerated and the RLi initiator is rapidly consumed. Of
course, additional RLi may be added to complete the
transformation of 1 to 4.
Cursory inspection of the data summarized in Table 1
reveals that cycloisomerization of 6-iodo-1-hexene (1) may
indeed be accomplished by treatment of 1 with either
MeLi or PhLi. A more detailed examination of the data
indicates that the outcome of the reaction depends
critically on the choice of solvent used for the isomeriza-
tion. The use of THF as solvent is to be avoided (Table
1, entry 5); the reaction of 1 with MeLi in THF is quite
rapid (15 min) but the bulk of the product (ca. >85%)
consists of alkanes derived from coupling of organo-
lithium and alkyl iodide intermediates.1,3 When con-
ducted in pure diethyl ether, the isomerization of 1 to 4
is accompanied by formation of significant quantities of
methylcyclopentane (Table 1, entries 1, 2, and 6). This
hydrocarbon is undoubtedly the result of protonation of
the intermediate (cyclopentylmethyl)lithium (3) by the
diethyl ether solvent since the simple expedient of
decreasing the proportion of ether in the solvent system
There is an additional feature of the isomerization
protocol that is not obvious from the product yields
reported in Table 1. Thus, whereas either MeLi or PhLi
may be used to effect conversion of 1 to 4, PhLi is by far

Li-I Exchange Mediated Atom Transfer Cyclization
J . Org. Chem., Vol. 63, No. 2, 1998 363
Sch em e 1
the better reagent for this purpose. During the early
stages of this research it was noted that reactions
conducted in the presence of MeLi failed to proceed to
completion unless a large excess (viz., >2 equiv) of the
reagent was employed. Indeed, a significant amount of
6-iodo-1-hexene (1) remains after prolonged treatment
with 1 molar equiv of MeLi (Table 1, entries 1-4).
Control experiments revealed that MeLi (but not alkyl-
lithium 2 or 3) was being removed from solution by fairly
rapid reaction with the methyl iodide generated in the
initial exchange (eq 1) to give ethane. Indeed, the
reaction of 0.1 M CH3Li with 0.1 M CH3I in Et2O at 22
°C cleanly produces ethane with a half-time of ap-
proximately 1.5 h. This sequestration of both MeLi and
CH3I over the time period needed for the cycloisomer-
ization of 1 (viz., 21 h at room temperature; Table 1, entry
1), effectively terminates the isomerization sequence (eqs
1 and 3).
There is no such difficulty when PhLi is used as
initiator and much less than a full molar equivalent of
this reagent serves to convert 1 to 4 in high yield (Table
1, entries 9-11). In fact, as required by the isomerization
sequence summarized above (eqs 1-3), the cycloisomer-
ization reaction is effectively catalytic in PhLi! Thus, as
illustrated below, allowing a 0.3 M solution of 1 in
scrupulously dry and deoxygenated pentane-diethyl
ether solution (9:1 by vol) to stand in the presence of 10
mol % of PhLi at room temperature for 18 h affords pure
(iodomethyl)cyclopentane (4) in 78% isolated yield (ca.
88% by GC) following workup and distillation. In prin-
ciple, a trace of PhLi should lead to complete conversion
of 1 to 4; in practice, it is exceedingly difficult to avoid
premature termination of the isomerization sequence via
inadvertent quench of organolithiums by proton abstrac-
tion from solvent or adventitious moisture when less than
∼10 mol % of PhLi is used to initiate the reaction.
The lithium-iodine exchange mediated isomerization
of 1 to 4 discussed above is superficially reminiscent of
the radical mediated iodine-transfer cyclization of 6-iodo-
1-hexenes that has been documented by Curran’s group.8
Indeed, the radical mediated isomerization of 1 to 4 is a
well-characterized process involving a chain mechanism
that may be initiated by even trace amounts of an alkyl
radical.8,9 Although a preponderance of evidence indi-
cates that the exchange reaction of an organolithium with
a primary alkyl iodide does not involve the generation of
radical intermediates,1,3b,10 it seemed imprudent to rely
solely on such precedent to exclude the possibility that
the conversion of 1 to 4 in the presence of MeLi or PhLi
was the result of a radical-chain process. In an effort to
address this issue, we investigated the reaction of MeLi
with two different alkyl iodide substrates (Scheme 2)
chosen on the basis of their ability to distinguish between
a radical-mediated process and one involving an anionic
intermediate. As demonstrated by the results presented
below, there is no evidence for the intermediacy of
radicals in reactions of MeLi (and by inference PhLi) with
primary alkyl iodide substrates incorporating the 5-hex-
enyl iodide moiety.
Reaction of 2-(allyloxy)ethyl iodide (5) with 1 equiv of
MeLi in Et2O at room temperature for 5 min results, as
shown in Scheme 2, in quantitative â-fragmentation to
give the lithium salt of allyl alcohol and ethylene along
with a 92% yield of CH3I. This behavior is characteristic
of the generation of (3-oxa-5-hexenyl)lithium via a
lithium-iodine exchange;11 the 3-oxa-5-hexen-1-yl radi-
cal, in contrast, is known to cyclize rapidly (k ) 8.5 ×
106 at 25 °C)12 to give the (3-tetrahydrofuranyl)methyl
radical. The reaction of an excess of MeLi with (E)-7-
iodo-1-methoxy-2-heptene (6) in Et2O at room tempera-
ture was also explored: Harms and Stille have previously
demonstrated that generation of (8-methoxy-5-heptenyl)-
lithium from this substrate by low-temperature ex-
The remarkable efficiency of the cycloisomerization
cascade (1 f 4) initiated by PhLi implies that the final
lithium-iodine equilibrium between (cyclopentylmethyl)-
lithium (3) and iodobenzene to give 4 and PhLi, depicted
generically in eq 3, must be quite one-sided. This aspect
of the isomerization sequence was investigated, following
the method pioneered by Applequist and O’Brien,2 by
determination of the apparent equilibrium constant7
(Kobs) for the rapid lithium-iodine exchange, 3 + PhI h
4 + PhLi, depicted in Scheme 1. While the highly biased
nature of this equilibrium (Scheme 1) precluded precise
determination of the apparent equilibrium constant (Kobs
) 340 ( 170), the result leaves little doubt that the
exchange between (cyclopentylmethyl)lithium (3) and
iodobenzene affords iodomethylcyclopentane (4) and PhLi
as required for successful operation of the catalytic cycle
(eqs 1-3).
(8) (a) Curran, D. P.; Chen, M.-H.; Kim, D. J . Am. Chem. Soc. 1986,
108, 2489. (b) Curran, D. P.; Kim, D Tetrahedron Lett. 1986, 27, 5821.
(c) Newcomb, M.; Curran, D. P. Acc. Chem. Res. 1988, 21, 206. (d)
Curran, D. P. Synthesis 1988, 417 and 489.
(7) Following Applequist and O’Brien,2 the apparent equilibrium
constant (Kobs) is derived (Scheme 1) on the assumption that both PhLi
and 3 are monomeric even though these organolithiums undoubtedly
exist as aggregates in pentane-ether solution;3 the actual degree of
aggregation of PhLi and 3 under the conditions of the equilibration
are unknown. The factors affecting the relationship of Kobs derived in
(9) Brace, N. O. J . Org. Chem. 1967, 32, 2711.
(10) (a) Bailey, W. F.; Patricia, J . J .; Nurmi, T. T.; Wang, W.
Tetrahedron Lett. 1986, 27, 1861. (b) Bailey, W. F.; Patricia, J . J .;
Nurmi, T. T. Tetrahedron Lett. 1986, 27, 1865.
(11) Bailey, W. F.; Punzalan, E. R.; Zarcone, L. M. J . Heteroat. Chem.
1992, 3, 55.
this way to the true equilibrium constant for
a
lithium-iodine
(12) (a) Smith, T. W.; Butler, G. B. J . Org. Chem. 1978, 43, 6. (b)
Beckwith, A. L. J .; Schiesser, C. H. Tetrahedron Lett. 1985, 26, 373.
exchange have been discussed.2

364 J . Org. Chem., Vol. 63, No. 2, 1998
Bailey and Carson
Sch em e 2
organolithiums have been previously described.4b The con-
centration of commercial solutions (Aldrich) of methyllithium
(MeLi) in diethyl ether and phenyllithium (PhLi) in cyclohex-
ane-diethyl ether (7:3 by vol) were determined immediately
prior to use by the method of Watson and Eastham.15 Product
mixtures were analyzed by GC on a 25-m × 0.20-mm cross-
linked, phenyl methyl (5%) silicone column using temperature
programming (30 °C for 16 min, 50 °C/min to 100 °C for 1 min,
and then 10 °C/min to 250 °C for 5 min).
Literature procedures, incorporating some minor modifica-
tions, were followed for the preparation of 6-iodo-1-hexene (1),16
2-(allyloxy)ethyl iodide (5),11 and (E)-7-iodo-1-methoxy-2-hep-
tene (6).13
Exp lor a tor y Rea ction s of 6-Iod o-1-h exen e (1) w ith
MeLi or P h Li. Approximately 0.1 M solutions of 1 (typically
0.5-1.0 mmol) containing an accurately weighed quantity of
a hydrocarbon internal standard (typically 0.3-0.4 mmol of
pure n-decane or cyclohexane) in the appropriate solvent
(Table 1) were stirred under an atmosphere of dry, oxygen-
free argon with 1.1 molar equiv of either MeLi or PhLi for a
period of time at various temperatures: specific conditions of
time and temperature are given in Table 1. Reaction mixtures
were quenched by cautious addition of water, washed with
water, dried (MgSO4), and analyzed by GC and GC/MS using
the column and conditions described in the General Procedures
to effect base-line separation of each component. Reaction
products were identified by comparison of their GC retention
times and mass spectra with those of authentic samples; yields
reported in Table 1 were corrected for detector response under
the conditions of the analysis using accurately weighed
samples of pure product and standard.
change with t-BuLi leads in good yield to vinylcyclopen-
tane and CH3OLi via intramolecular SN′ cyclization.13 In
the event, as illustrated in Scheme 2, prolonged treat-
ment of 6 with 2.3 molar equiv of MeLi afforded vinyl-
cyclopentane in 78% yield as expected from reaction
involving reversible formation (eq 1) of (8-methoxy-5-
heptenyl)lithium. It might be noted that a large excess
of MeLi is required for this transformation since, as noted
above, a significant quantity of the reagent is consumed
by reaction with the cogenerated methyl iodide and no
channel exists, following expulsion of lithium methoxide
in the SN′ cyclization, for regeneration of the alkyllithium.
The radical-mediated cyclization of 6 (n-Bu3SnH, AIBN
in benzene at 80 °C; Scheme 2), which has not to our
knowledge been previously reported, proceeds as expected
to give an essentially quantitative yield of (2-methoxy-
ethyl)cyclopentane. In light of these results (Scheme 2)
and the data reported above, it seems improbable that
the lithium-iodine exchange initiated rearrangement of
1 to 4 is other than an anionic atom transfer process.
Con clu sion s
Utilization of a reversible lithium-iodine exchange
reaction to mediate isomerization of 6-iodo-1-hexene (1)
to (iodomethyl)cyclopentane (4) provides a novel example
of a highly atom-economical transformation.14 The cata-
lytic cycle illustrated below, involving exchange-cycliza-
tion-exchange (eqs 1-3), provides an exceedingly simple
method for the preparation of cyclopentanes bearing a
CH2I group that is then available for further transforma-
tion. We are currently exploring application of this
methodology for the construction of polycyclic systems by
multiple exchange-initiated cyclization of polyolefinic
alkyl iodides.
Isom er iza tion of 6-Iod o-1-h exen e (1) to (Iod om eth yl-
)cyclop en ta n e (4) in th e P r esen ce of Ca ta lytic P h Li. A
flame-dried 50-mL, one-necked, round-bottomed flask, equipped
with a Teflon-coated stir bar and capped with a septum, was
charged with a solution of 2.21 g (10.5 mmol) of 6-iodo-1-
hexene (1) in 27 mL of n-pentane and 3 mL of diethyl ether,
and 0.63 mL of a 1.72 M solution of PhLi (1.08 mmol) in
cyclohexane-diethyl ether (7:3) by volume was added in one
portion. The resulting pale-yellow solution was stirred for 18
h at 22 °C under an atmosphere of argon and then quenched
with water. The organic layer was washed with brine and
dried (Na2SO4), and solvent was removed by careful distillation
at atmospheric pressure. Ku¨gelrohr distillation of the residue
afforded 1.72 g (78%) of (iodomethyl)cyclopentane (4): bp (bath
1
temperature) 90-95 °C (38 mm) [lit.17 bp 75 °C (19 mm)]; H
NMR (CDCl3) δ 1.18-1.23 (m, 2 H), 1.55-1.68 (m, 4 H), 1.80-
1.84 (m, 2 H), 2.15 (7-line pattern, J ) 7.57 Hz, 1 H), 3.19 (d,
J ) 7.57 Hz, 2 H); 13C NMR (CDCl3) δ 14.21, 25.50, 33.38,
42.66.
Eva lu a tion of th e Ap p a r en t Equ ilibr iu m Con sta n t for
th e Lith iu m -Iod in e Exch a n ge betw een (Cyclop en tyl-
m eth yl)lith iu m (3) a n d Iod oben zen e To Give (Iod om -
eth yl)cyclop en ta n e (4) a n d P h Li. A solution of 218 mg
(1.04 mmol) of 6-iodo-1-hexene (1) in 9 mL of n-pentane and 1
Exp er im en ta l Section
Gen er a l P r oced u r es. Spectroscopic and chromatographic
procedures, methods used for the purification of reagents and
solvents, and precautions regarding the manipulation of
(15) Watson, S. C.; Eastham, J . F. J . Organomet. Chem. 1967, 9,
165.
(16) Bailey, W. F.; Gagnier, R. P.; Patricia, J . J . J . Org. Chem. 1984,
49, 2098.
(17) Zelinsky, N. D.; Michlina, S. E.; Eventowa, M. S. Chem. Ber.
1933, 66, 1422.
(13) Harms, A. E.; Stille, J . R. Organometallics 1994, 13, 1456.
(14) (a) Trost, B. M. Science 1991, 254, 1471. (b) Trost, B. M. Angew.
Chem., Int. Ed. Engl. 1995, 34, 259.

Li-I Exchange Mediated Atom Transfer Cyclization
J . Org. Chem., Vol. 63, No. 2, 1998 365
mL of diethyl ether, containing 79.2 mg (0.558 mmol) of
n-decane as internal standard, was cooled under an atmo-
sphere of argon to -78 °C and 1.57 mL of a 1.45 M solution of
t-BuLi (2.28 mmol) in heptane was added dropwise. The
reaction mixture was stirred for an additional 5 min at -78
°C, the cooling bath was then removed, and the reaction
mixture was stirred at room temperature for 1 h to complete
formation of (cyclopentylmethyl)lithium (3) and to remove
residual t-BuLi.1 The flask was recooled to -78 °C, 194 mg
(0.953 mmol) of iodobenzene was added, and the reaction
mixture was stirred for 30 min at -78 °C before quench by
rapid addition of 1 mL of MeOD. The mixture was allowed to
warm to room temperature and was then washed with water
and dried (MgSO4). Quantitative analysis of the reaction
product by GC, as well as independent GC/MS determination
of the d1-content of methylcyclopentane, indicated that the
following compounds were present in the quenched equilibra-
tion mixture: methylcyclopentane (0.115 mmol; d1-content )
(15 ( 5)%), benzene (0.859 mmol which was assumed to be
100% monodeuterated; the significant M+ - 1 ion in the mass
spectrum of benzene precluded accurate determination of the
high d1-content), iodobenzene (0.121 mmol), and (iodomethyl-
)cyclopentane (4, 0.825 mmol). The apparent equilibrium
constant was evaluated as: Kobs ) [4][C6H5D]/[c-C5H9-CH2D]-
[PhI] ) 340 ( 170.
Rea ction of 2-(Allyloxy)eth yl Iod id e (5) w ith MeLi.
Neat 2-(allyloxy)ethyl iodide (5), 163 mg (0.769 mmol), con-
taining 51.0 mg (0.607 mmol) of cyclohexane as internal
standard, was added at 22 °C over a 5 min period to 6.00 mL
of a 0.15 M solution of MeLi (0.90 mmol) in ether-pentane
(1:5 by vol), and the resulting mixture was stirred at 22 °C
for an additional 5 min. J ust enough saturated, aqueous
ammonium chloride was added to form a clear organic layer,
and the organic extract was dried (MgSO4). GC analysis
revealed that the reaction had produced allyl alcohol (∼100%)
and iodomethane (92%).
Rea ction of (E)-7-Iod o-1-m eth oxy-2-h ep ten e (6) w ith
MeLi: P r ep a r a tion of Vin ylcyclop en ta n e. A solution of
231 mg (0.911 mmol) of (E)-7-iodo-1-methoxy-2-heptene (6) in
10 mL of diethyl ether was treated with 1.14 mL of a 1.83 M
solution of MeLi (2.09 mmol) in diethyl ether, and the resulting
mixture was stirred under argon at room temperature for 26
h before the addition of 1 mL of water. After drying (MgSO4),
GC and GC/MS analysis of the product mixture revealed that
the reaction afforded vinylcyclopentane (∼78%) and (2-meth-
oxyethyl)cyclopentane (∼9%) along with approximately 7% of
unreacted 6.
Ra d ica l-Med ia ted Cycliza tion of (E)-7-Iod o-1-m eth -
oxy-2-h ep ten e (6): P r ep a r a tion of (2-Meth oxyeth yl)-
cyclop en ta n e. A solution of 99.1 mg (0.389 mmol) of (E)-7-
iodo-1-methoxy-2-heptene (6) in 10 mL of dry benzene was
heated to reflux under an atmosphere of argon, and a solution
of 1.20 mL (0.446 mmol) of tributyltin hydride and ∼6.6 mg
of AIBN in 5 mL of benzene was added via a syringe pump
over a 4.5 h period. The resulting mixture was cooled to room
temperature and concentrated. GC analysis of the concentrate
indicated that the reaction afforded the title ether in virtually
quantitative yield. A pure sample of the known ether,18 free
of tin impurities, was isolated by preparative GC on a 10-ft,
10% SE-30 on Anakrom A (60/80 mesh) column at 122 °C:
1H NMR (CDCl3) δ 1.05-1.10 (m, 2H), 1.48-1.60 (m, 6 H),
1.72-1.85 (m, 3 H), 3.31 (s, 3 H), 3.36 (t, J ) 6.92 Hz, 2 H);
13C NMR (CDCl3) δ 25.03, 32.69, 35.82, 36.89, 58.55, 72.37.
Ack n ow led gm en t. We are grateful to Mr. Eric
DeLeon for the preparation of iodide 6 used in this
study. This work was supported by a grant from the
Connecticut Department of Economic Development.
J O971939E
(18) Tanida, H.; Tsuji, T.; Irie, T. J . Am. Chem. Soc. 1966, 88, 864.