Cyclizations in the homolytic reactions of unsaturated nitriles with tert-butylmercury halides in the presence of proton donors

Article abstract of DOI:10.1002/(SICI)1099-1395(1998100)11:10<715::AID-POC30>3.0.CO;2-E

Cyclizations are observed in the homolytic reactions of t-BuHgI with CH₂=CHCH₂YCH₂CN [Y = CH₂, O, CMe₂, C(CO₂Et)₂, NCH₂CN] and CH₂=CHCH₂CH_2<

Full text of DOI:10.1002/(SICI)1099-1395(1998100)11:10<715::AID-POC30>3.0.CO;2-E

JOURNAL OF PHYSICAL ORGANIC CHEMISTRY, VOL. 11, 715–721 (1998)
Cyclizations in the homolytic reactions of unsaturated
nitriles with tert-butylmercury halides in the presence of
proton donors†
Glen A. Russell* and Ping Chen
Department of Chemistry, Iowa State University, Ames, Iowa 50011, USA
Received 17 October 1997; revised 6 January 1998; accepted 11 January 1998
ABSTRACT: Cyclizations are observed in the homolytic reactions of t-BuHgI with CH2 CHCH YCH CN
2
2
epoc
[
Y = CH , O, CMe , C(CO Et) , NCH CN] and CH CHCH CH YCH CN [Y = CH , O, C(CO Et) ] in Me SO in
2 2 2 2 2 2 2 2 2 2 2 2 2
_
the presence of hydriodic acid. Only with Y = C(CO Et) does the adduct radical, t-BuCH CHCH YCH CN, undergo
2
2
2
2
2
facile 5-exo cyclization in the absence of a proton donor. The other 5-exo and all 6-exo cyclizations require substrate
‡
�
_
protonation to yield t-BuCH CH(CH ) YCH C NH (n = 1, 2), which cyclizes readily to the iminium radical cation
2
2 n
�
2
followed by electron transfer with I or t-BuHgI2 to form the imine as a precursor to the cyclopentanone or
cyclohexanone upon hydrolysis. For CH2 CHCH C(CO Et) CH CN the formation of the cyclopentanone is
2
2
2
2
dramatically promoted by NH I in the dark in the absence of any other acid. In this case, where cyclization of the
4
adduct radical occurs readily without substrate activation, protonation of the cyclized iminyl radical allows the
�
�
.
electron transfer with I or t-BuHgI2 to occur with regeneration of t-Bu . A similar effect is observed with
CH2 CHCH C(CO Et) CH N where only a slow reaction is observed upon photolysis with t-BuHgI in the absence
of NH I, although apparently cyclization of t-BuCH CHCH C(CO Et) CH N (with loss of N ) occurs readily. In the
2
2
2
2 3
_
4
2
2
2
2
2
3
2
presence of NH I the cyclized aminyl radical can be protonated and the resulting amine radical cation readily reduced
4
�
�
by I or t-BuHgI2 to continue a chain process. With the thioesters CH2 CHCH YCH C(O)SPh [Y = O, CH ,
2
2
2
CMe , C(CO Et) ], significant cyclization upon photolysis with t-BuHgX occurred only for Y = C(CO Et) .  1998
2
2
2
2
2
John Wiley & Sons, Ltd.
KEYWORDS: unsaturated nitriles; homolytic reactions; cyclization; tert-butylmercury halides; proton donors
Additional material for this paper is available from the epoc website at http://www.wiley.com/epoc
INTRODUCTION
(3–10) which increase for CH2 CHP(O)(OH)
OCH CH CH , CH2 CHC(O)OC(Me )CH CH or
2
2
2
2
tert-Butylmercury halides will form the 1:1 adducts with
CH2 CHC(O)N(CH CH CH ) to 50–200, whereas
dark reactions, initiated by t-BuHgI–KI at 25°C, give
2 2 2
2
terminal alkenes when irradiated with a fluorescent
1
sunlamp at 35°C in Me SO solution:
initial chain lengths of 4300 for the allyl vinylphos-
2
1
phonate and ca 20 000 for N,N-diallylacrylamide. We
h ꢀ;5 h
CH2 CHBu ‡ t-BuHgX �ꢀ t-BuCH CH(HgX)Bu ꢁ1†
2
have extended these studies to additive cyclizations of !-
unsaturated nitriles, azides and thioesters, functional
groups recognized to participate in 5-exo cyclizations,
X ˆ Cl ꢁ40%†; X ˆ I ꢁ43%†
The adduct can be reduced to the alkane by NaBH or
4
primarily in the reactions of low concentrations of R SnH
3
converted to t-BuCH CH(SPh)Bu in 95% yield by
2
.
or molar equiv. of Bu SnSnBu with appropriately
3 3
photolysis with Ph S . As measured by (t-Bu) NO
2
2
2
substituted alkyl halides or thionocarbamates, e.g.
inhibition, the rate of adduct formation is only slightly
greater (ca 40%) than the rate of formation of radicals
trapped by the nitroxide. With 1,6-dienes or enynes the
cyclized organomercurials are formed in free radical
chain reactions with modest initial kinetic chain lengths
3–5
according to the equation.
†
*
Electron Transfer Processes. Part 65.
Deceased 1997, correspondence to: M. Russell, Department of
Chemistry, Iowa State University, Ames, Iowa 50011, USA.
E-mail: grussell@iastate.edu
Contract/grant sponsor: National Science Foundation; contract grant
number: CHE-9220639.
Contract/grant sponsor: Petroleum Research Fund; contract grant
number: 32021-AC4.
Radical cyclizations leading to cycloalkanones are also

1998 John Wiley & Sons, Ltd.
CCC 0894–3230/98/100715–07 $17.50

7
16
G. A. RUSSELL AND P. CHEN
0
‡
0
‡
R CH(Ph)NR_‡ H „ R CH(Ph)NHR_
CH2 CH(CH ) CN a much stronger acid (hydriodic
2 3
0
_
‡
0
‡
acid) was required to bring about cyclization. Apparently,
R CH2CHCꢂN ‡ H „ R CH2CH
C
NH_
.
for CH (CH ) CN cyclization is too slow for protonation
0
0
‡
0
�
00
0
2
2 3
R NHR_ ‡ R HgI2 ꢀ R NHR ‡ R _‡ HgI
2
of the cyclized radical to promote a homolytic chain
reaction significantly and promotion is observed only
with acids strong enough to give both substrate and
0
‡
0
�
0
0
R CH2CH
C
NH_ ‡ R HgI2 ꢀ R CH2CH
Scheme 1. R' = t-Bu.
C
NH ‡ R _‡ HgI2
17
radical activation (Scheme 2).
observed in the oxidative decarboxylation of !-cyano-
carboxylic acids, in Mn(III) oxidations of b-diketones
6
RESULTS AND DISCUSSION
g-Cyanoalkenes
yielding, after an initial cyclization, 4- or 5-cyanoalkyl
7
radicals, and in the intramolecular addition of ketyls, or
their trimethylsilyl derivatives, to g- or ꢁ-unsaturated
nitriles.
8
,9
Table 1 summarizes results for the reaction
Initial experiments with t-BuHgX (X = Cl, I) and
CH2 CH(CH ) CN led only to the uncyclized 1:1
2 3
adducts in yields comparable to those observed for 1-
hexene. This was not surprising because the 5-exo
.
cyclization of CH (CH ) CN is known to occur with a
2
2 3
3
� 1
rate constant of only 4 Â 10 s
at 25°C, a value
.
approximately 1/25th that of CH CH CH CH and 1/
2
2
2
.
10
6
0th that of CH (CH ) CH CH2. The 5-exo cycliza-
2 2 3
.
11
tion of CH (CH ) CN is only slightly exothermic, and
2
2 3
10b
although the cyclization is irreversible at � 14°C, ring
opening of the cyclopentyliminyl radical occurs readily at
1
1,12
>
250°C.
Moreover, homolytic 1,4-shifts of cyano
groups have been observed to occur readily at 25–80°C
In the presence of KI, NH I or PTSA, small amounts of
4
.
1
2
1
for CH (CH ) C(R )(R )CN, particularly when R = OH
1a were observed in addition to the uncyclized 1:1
adduct. However, significant amounts of 1a were formed
only in the presence of 2–4 equiv. of hydriodic acid or
PTSA and iodide salts. It does not appear that non-
ionized HI is acting as a chain transfer agent because
t-Bu(CH ) CN is not observed as a reaction product.
2
2 2
2
13,14
or alkyl and R = alkyl, aryl or CO Et.
In view of
2
these results, we reasoned that if reversible cyclization
was occurring, the cyclized radical should be converted
to the imine by the presence of a proton donor and iodide
ion, a combination that has proven to be efficient for the
2
4
1
5
reductive alkylation of imines
or a,b-unsaturated
nitriles, even with NH4 as the proton donor (Scheme
). Indeed, NH I was an excellent promoter for additive
Apparently substrate protonation (Scheme 2) leads to
promotion of the cyclization reaction leading to the easily
reduced iminium ion.
1
6
‡
1
4
cyclizations of CH2 CHCH C(CO Et) CH CN or
Similar
results
were
observed
for
2
2
2
2
CH2 CH(CH ) N
in
Me SO
but
with
CH2 CHCH OCH CN, CH CHCH C(Me) CH CN
2 3
3
2
2
2
2
2
2
2
and CH2 CHCH N(CH CN) with significant yields
2
2
2
of 1b–d observed only in the presence of hydriodic acid
Table 1). However, with CH2 CHCH C(CO Et)
2
(
2
2
CH CN the formation of 1e was significant with t-BuHgI
2
alone, with the yield improved only slightly by the
presence of hydriodic acid. With the gem-diester,
cyclization must occur readily to yield the iminyl radical
which is trapped by t-BuHgI to form the imine and/or its
Hg(II) salt as a precursor to 1e. The reaction will now
�
occur in the dark in the presence of I [The thermal
.
�
formation of t-Bu at 25°C from t-BuHgI–I may involve
comproportionation to form the labile (t-Bu) Hg ], and
2
2
under this condition there is a dramatic promotion by the
‡
presence of NH . The iminyl radical is apparently
4
‡
protonated by NH4 to form the iminium ion, which
reacts with t-BuHgI2 or I (Scheme 1) more readily
than the iminyl radical reacts with t-BuHgI. The dark
�
�
Scheme 2. R = t-Bu.
1998 John Wiley & Sons, Ltd.
reactions with NH I are inhibited for 2–3 weeks by the
4

JOURNAL OF PHYSICAL ORGANIC CHEMISTRY, VOL. 11, 715–721 (1998)

CYCLIZATIONS IN HOMOLYTIC REACTIONS OF UNSATURATED NITRILES WITH t-BuHgX
717
a
Table 1. Photolysis of t-BuHgX with CH2 CHCH ÐYÐCH CN
2
2
b
Y
X (equiv.)
Additive (equiv.)
KI (8)
Time (h)
Product (%)
CH2
CH2
CH2
CH2
CH2
CH2
CH2
O
C(Me)2
C(Me)2
NCH CN
C(CO Et)
C(CO Et)
Cl (4)
Cl (4)
Cl (4)
I (4)
I (4)
I (4)
I (4)
I (4)
I (4)
I (4)
I (4)
I (4)
I (4)
I (4)
I (4)
16
12
12
12
12
12
20
24
12
12
12
12
8
1a (4)
1a (8)
1a (8)
1a (7)
NH I (8)
4
PTSA (4)
PTSA (4)
PTSA (4), KI (4)
Aq. HI (4)
1a (20)
1a (41)
1a (55)
1b (60)
1c (10)
1c (55)
1d (34)
1e (74)
1e (80)
Aq. HI (2)
Aq. HI (2)
NH I (4)
4
Aq. HI (2)
Aq. HI (4)
None
Aq. HI (2)
KI (2)
2
2
2
2
2
2
2
c
C(CO Et)
C(CO Et)
24
18
1e (10)
2
c
NH I (2)
1e (78)
2
4
a
0
.13 M nitrile in Me
2
SO-d
6
irradiated by a 275 W fluorescent sunlamp at 35–40°C. The use of Me
2 6
SO-d allowed the reactions to be monitored by
1
b
c
H NMR.
By H NMR with PhCH
Dark reactions at 25°C.
1
3
as an internal standard after workup with aq. Na
2 2 3
S O .
.
presence of 10 mol% of (t-Bu) NO , indicating an
appreciable kinetic chain length for the homolytic
reaction. 4,4-Dimethyl-5-hexenenitrile was much less
reduced by both the reactions of Scheme 1 and by the
reactions
2
15
reactive than its 3,3-dimethyl isomer, presumably
because of steric hindrance in the addition of t-Bu to
�
ꢃ
_
.
RCHCN ‡ t-BuHgI �ꢀ RCH(CN)HgI � ‡ t-Bu ꢁ5†
2
2
RCH(CN)HgI2 ‡ NH4‡ �ꢀ
�
form a neopentyl-type radical. Even in the presence of
hydriodic acid only a 10% yield of 3,3-dimethyl-2-(2,2-
dimethylpropyl)cyclopentanone was observed under the
conditions employed in Table 1. 2,2-Dimethyl-5-hex-
enenitrile also gave a lower yield of the cyclopentanone
RCH CN ‡ NH ‡ HgI ꢁ6†
2
3
2
Reactions of ꢁ-cyanoalkenes (CH2 CHCH —X—Y—
2
CH CꢂN) with 4 equiv. of t-BuHgI and 2 equiv. of
(34%) than the 3,3-dimethyl isomer.
2
hydriodic acid in Me SO with sunlamp irradiation for
2
16 h thus formed a mixture of the cyclohexanones 2 and
the uncyclized reductive tert-butylation products 3
(Table 2):
d-Cyanoalkenes
-Exo cyclizations of CH (CH ) CN routinely occur
.
6
2
2 4
less efficiently than 5-exo cyclizations of the 4-cyano
homologs, in part because of 1,5-hydrogen atom
5
,18,19
shifts:
_
_
t-BuCH CH(CH † CN �ꢀ t-Bu(CH † CHCN ꢁ4†
2
2 4
2 4
In the presence of NH I, 1-cyanoalkyl radicals are
4
Table 2. Photolysis of t-BuHgI with CH CHCH ÐXÐYÐ
2
2
a
CH CN
2
Only in the formation of 2b/3b and 2c/3c did the
b
X
Y
Products (%)
cyclized product predominate over the 1,5-hydrogen
atom transfer product. The formation of 3 must be a result
of the 1,5-hydrogen atom rearrangement because analo-
gous reductive alkylation products were not observed
with g-cyanoalkenes or 1-hexene. In addition, photolysis
of CH2 CH(CH ) CMe CN with t-BuHgI–HI produced
CH2
CH2
CH2
CH2
O
2a (9)
3a (29)
3b (12)
3c (26)
3d (33)
2b (25)
2c (34)
2d (22)
C(CO Et)2
2
C(CO Et)
CH2
2
2
a
2 3
2
See Table 1. Reactions were photolyzed for 16 h.
After hydrolysis with aq. Na
b
mainly the uncyclized 1:1 adduct (42%), ca 2% of the
2
S O
2 3
; see Table 1.

1998 John Wiley & Sons, Ltd.
JOURNAL OF PHYSICAL ORGANIC CHEMISTRY, VOL. 11, 715–721 (1998)

7
18
G. A. RUSSELL AND P. CHEN
cycloalkanone and no significant amounts of the
reductive alkylation product analogous to 3.
with Y = CMe while a fairly good yield (65%) of 1e was
2
obtained with Y = C(CO Et) by photolysis with 4 equiv.
2
2
Two e-cyanoalkenes were examined neither of which
gave any indication of 7-exo cyclization. Photolysis of
CH2 CHCH CH C(CO Et) CH CH CN with t-BuHgI–
of t-BuHgCl in Me SO at 35–40°C for 18 h. We
2
conclude that the rates of 5-exo cyclization are greater
for the nitriles than for the S-phenyl thioates and that
in both systems the rates of cyclization of
2
2
2
2
2
2
HI gave the 1:1 adduct in 45% yield together with 19% of
_
the reductive alkylation product, t-Bu(CH ) C(CO Et)
t-BuCH CHCH YCH Q [Q = CN,C(O)SPh] increase
2
3
2
2
2
2
2
CH CH CN, possibly from a 1,5- or 1,6-hydrogen atom
from Y = CH to CMe to C(CO Et) , paralleling the
2
2
2 2 2 2
1
transfer.WithCH2 CHCH OCH C(Me) CH CNphoto-
substituent effects noted with Q = CH CH . The effect
2
2
2
2
2
lysis with t-BuHgI–HI for 7 h gave ca 90% of t-
BuCH CH CH from a b-elimination process. b-Elim-
of gem-diester substitution at C-3 in 5-hexenyl radical
cyclizations is significant and apparently more important
than gem-dimethyl substitution; the latter has been pre-
viously recognized to enhance cyclizations in 3-bute-
2
2
ination in the reactions of t-BuHgX with allyl alcohol and
its derivatives has been previously observed to proceed
via t-BuCH CH(HgX)CH OY with Y = H, Ph, Ac,
24
25
26
_
nyl, 4-pentenyl, 5-hexenyl or t-BuCH CHC(O)OC
2
2
2
2
0,21
1
Bz.
Similar reactions occur for propargyl alcohol
(Me) CH CH radicals. A similar effect apparently
2
2
derivatives. The elimination appears to be an E process
which is promoted by nucleophiles such as I .
occurs in 6-exo cyclizations as judged from the results
with ꢁ-cyanoalkenes. In the 5-hexenyl cases the effect of
substitution at C-3 is presumably a result of rotamer
populations with the sickle conformation required for a
radical cyclization more highly populated with ester
2
20
�
Other 5-exo-cyclization
25b,27
substituents.
Cyclizations involving thio esters were examined be-
Cyclization was also observed upon photolysis of
1
2
˙
cause the formation of (R )(R )C(O )SPh and b-elimina-
t-BuHgCl with CH2 CHCH C(CO Et) CH N in
2
2
2
2 3
.
tion of PhS should be irreversible. Intermolecular radical
Me SO in the presence of NH I. Azides are known to
2 4
substitution in HC(O)SPh has been reported to occur in
low yield upon photolysis with PhO(CH ) I in the
be attacked by radicals to yield aminyl radicals,
28
˙
particularly by Bu Sn :
2
4
3
2
2
presence of Bu SnSnBu , while analogous intramole-
3
3
ꢃ
_
RN ‡ Bu Sn �ꢀRNSnBu ‡ N
ꢁ7†
cular cyclizations involving ꢁ- or e-halo S-phenyl
3
3
3
2
thioesters gave good yields of cyclized products,
.
23
In the case of attack of t-Bu
upon
particularly with gem-disubstituted !-iodo thioesters.
The allyl ethers CH2 CHCH OCH C(O)X with
CH2 CHCH C(CO Et) CH N , it was not clear if the
2
2
2
2 3
2
2
initial point of attack would be at the azide group or at the
X = PhS, OH or OEt were examined because
CH2 CHCH OCH CN had given a good cyclization
29
carbon–carbon double bond. The product observed (4)
2
2
in 50% yield clearly requires initial attack at the carbon–
carbon double bond followed by cyclization with the loss
of nitrogen:
reaction (Table 1). However, photolysis with t-BuHgCl
initially formed only the 1:1 uncyclized adducts. In PhH
the adducts were stable to further photolysis and could be
isolated or reduced by NaBH to give the reductive
4
alkylation products. In Me SO the adducts decomposed
2
to form t-BuCH CH CH without any indication of the
2
2
formation of cyclized products. Since cyclization by the
combination of the reactions in Scheme 3 still seemed
reasonable in the absence of a b-elimination processes,
we
examined
the
S-phenyl
5-hexenethioates
CH2 CHCH YCH C(O)SPh with Y = CH , CMe and
2
2
2
2
C(CO Et) . Although only a trace of 1a was observed
Little reaction was observed in the absence of NH4I
while the azide was destroyed by the use of PTSA or
2
2
with Y = CH , a modest 18% yield of 1c was observed
2
Scheme 3. R = t-Bu.
JOURNAL OF PHYSICAL ORGANIC CHEMISTRY, VOL. 11, 715–721 (1998)

1998 John Wiley & Sons, Ltd.

CYCLIZATIONS IN HOMOLYTIC REACTIONS OF UNSATURATED NITRILES WITH t-BuHgX
719
hydriodic acid as promoters. The reaction appears to fit
Scheme 1 where the aminyl radical formed by addition
followed by cyclization reacts slowly with t-BuHgX to
propagate the chain reaction. In the presence of NH4 the
aminyl radical can be protonated to give an aminium
completion of the reaction the products were poured into
a saturated aqueous Na S O solution and extracted by
2
2 3
1
CH Cl . The products were analyzed by GC–MS and H
2
2
‡
NMR using toluene as an internal standard for yield
determination. Products were isolated by flash column or
thin-layer chromatography using silica gel with hexane–
ethyl acetate as the eluent.
radical cation readily reduced to the amine by iodide ion
�
or t-BuHgI . Either reaction continues the chain because
2
.
1
13
iodine atom readily displaces t-Bu from t-BuHgI.
H and C NMR spectra were recorded at 300 and
Although cyclizations in the photolysis of t-BuHgCl
75.4 MHz and are reported in ppm from internal Me Si or
4
with CH2 CHC(O)OCMe CH CH , CH CHC(O)
the central line of CDCl at 77.00 ppm, respectively.
2
2
2
3
OCMe CꢂCH or CH2 CHC(O)N(CH CH CH )
Electron ionization (EI) mass spectra at 70 eV were
obtained in the GC mode with a Finnegan 4000
spectrometer and in the HR mode with a Kratos MS-50
spectrometer. FTIR spectra were recorded on IBM 1898
or Digital FTS-7 spectrometers.
2
2
2 2
occur, the corresponding cyclizations in the reactions of
CH2 CHC(O)OCMe CN or CH2 CHC(O)N(CH CN)2
2
2
were not observed. Reactions with t-BuHgI–KI in the
dark formed the uncyclized 1:1 adducts in high yield
whereas reactions in the presence of NH I, PTSA or
hydriodic acid formed only their protonolysis products,
The preparation of t-BuHgX has been described
4
1,2
previously. Substrates employed were synthesized by
standard methods and are described in the Supplementary
Material.
t-BuCH CH C(O)OCMe CN or t-BuCH CH C(O)N
2
2
2
2
2
1
(
CH CN) , in essentially quantitative yields. In a similar
2 2
fashion, CH2 CHC(O)OCH C(O)SPh formed only the
2
uncyclized 1:1 adduct which could be protonated or
2-(2,2-Dimethylpropyl)cyclopentanone (1a). The pro-
reduced by Et SiH to t-BuCH CH C(O)CH C(O)SPh.
duct was isolated as a liquid: IR (neat), 2958, 2868,
3
2
2
2
�
1 1
Even photolysis of the adduct with Ph S , a process
1742 cm ; H NMR (CDCl ), ꢁ 0.92 (s, 9 H), 1.05 (dd,
2
2
3
which led to cyclization for t-BuCH CH(HgI)C(O)OCH2
J = 14.1, 9.0 Hz, 1 H), 1.43–1.57 (m, 1 H), 1.68–1.82 (m,
1 H), 1.88 (dd, J = 14.1, 2.4 H, 1 H), 1.92–2.12 (m, 3 H),
2
CH CH or t-BuCH CH(HgI)C(O)OCH CꢂCH, failed
2
2
2
13
to yield cyclized products. 5-Exo cyclizations of ester or
amide radicals are more difficult than the cyclizations of
simple 5-hexenyl radicals while the —CꢂN or
2.25–2.43 (m, 2 H); C NMR (CDCl ), ꢁ 20.80, 29.77,
3
30.47, 32.74, 37.37, 44.13, 46.77, 221.85; MS, m/z
‡
154.1361 (calculated for M 154.1358), 139 (14), 125
—C(O)SPh groups are less reactive in 5-exo attack than
(11), 112 (28), 97 (29), 83 (32), 57 (100).
—
CH CH or —CꢂCH groups.
2
�
Reaction of t-BuHgI–I with CH CHC(O)OCH2
4-(2,2-Dimethylpropyl)tetrahydrofuran-3-one (1b). The
2
1
CH N in Me SO failed to occur in the dark at room
product was isolated as a liquid: H NMR (CDCl ), ꢁ 0.91
2
3
2
3
temperature. This was surprising because various acry-
late esters, including CH2 CHCO CH CH Br, gave
(s, 9 H), 1.16 (dd, J = 14.4, 9.6 Hz, 1 H), 1.87 (dd,
J = 14.4, 2.4 Hz, 1 H), 2.39–2.50 (m, 1 H), 3.69 (dd or t,
J = 9.6 Hz, 1 H), 3.74 (dd, J = 17.1, 0.6 Hz, 1 H), 4.08
2
2
2
essentially quantitative yields of the 1:1 adduct in 0.5–1 h
1
by a free radical chain reaction. Photolysis of
(dd, J = 17.1, 1.2 Hz, 1 H), 4.60 (dd or t, J = 9.0 Hz, 1 H);
�
13
CH2 CHCO CH CH N with t-BuHgI–I yielded only
C NMR (CDCl ), ꢁ 29.52, 30.24, 41.91, 44.98, 70.33,
2
2
2
3
3
‡
the reductive alkylation product, although in low yield
24% after 6 h), even in the absence of a proton donor.
74.28, 217.11; MS, m/z 156.1148 (4) (calculated for M
(
156.1150), 141 (3), 114 (5), 83 (23), 57 (100).
This suggests that 1,5-hydrogen atom transfer is greatly
facilitated by the azido group to yield t-BuCH2
2-(2,2-Dimethylpropyl)-4,4-dimethylcyclopentanone
(1c). The compound was isolated as a liquid: H NMR
.
1
CH CO CH CHN , which does not readily continue a
2
2
2
3
�
chain reaction with t-BuHgI–I but which under forcing
(CDCl ), ꢁ 0.91 (s, 9 H), 1.07 (dd, J = 13.8, 9.6 Hz, 1 H),
3
conditions can be converted to t-BuCH CH2
1.07 (s, 3 H), 1.17 (s, 3 H), 1.41–1.49 (m, 1 H), 1.89 (dd,
2
13
CO CH CH N .
J = 13.8, 2.4 Hz, 1 H), 1.95–2.33 (m, 4 H); C NMR
CDCl ), ꢁ 27.92, 29.74, 29.78, 30.53, 34.10, 45.31,
2
2
2 3
(
3
4
5.65, 47.23, 52.49, 221.96; MS, m/z 182.1675 (16)
‡
EXPERIMENTAL
(calculated for M 182.1671), 167 (13), 125 (85), 111
(22), 98 (17), 83 (26), 69 (29), 57 (100).
Substrates (0.5–1 mmol), t-BuHgX and any other
reagents were added to Pyrex tubes containing 4–10 ml
5-(2,2-Dimethylpropyl)-2,2-dimethylcyclopentanone.
The product was isolated as a liquid: H NMR (CDCl ), ꢁ
1
of deoxygenated Me SO under a nitrogen atmosphere.
2
3
The solutions were stirred in the dark at ca 25°C with the
tube wrapped in aluminum foil or irradiated with a 275 W
Sylvania fluorescent sunlamp ca 25 cm from the reaction
tube at 35–40°C. Reactions were conveniently monitored
0.92 (s, 9 H), 0.94 (s, 3 H), 1.08 (dd, J = 13.8, 9.3 Hz, 1
H), 1.08 (s, 3 H), 1.46–1.70 (m, 2 H), 1.78–1.85 (m, 1 H),
1.89 (dd, J = 14.1, 2.4 Hz, 1 H), 2.02–2.12 (m, 1 H),
13
2.20–2.30 (m, 1 H); C NMR (CDCl ), ꢁ 23.76, 24.70,
3
1
by H NMR by the use of Me SO-d as solvent. Upon
28.98, 29.84, 30.64, 36.84, 44.36, 45.55, 46.11, 225.12;
2
6

1998 John Wiley & Sons, Ltd.
JOURNAL OF PHYSICAL ORGANIC CHEMISTRY, VOL. 11, 715–721 (1998)

7
20
G. A. RUSSELL AND P. CHEN
‡
MS, m/z 182.1669 (26) (calculated for M 182.1671),
67 (16), 125 (58), 112 (22), 111 (19), 83 (22), 57 (100).
1.61 (m, 1 H), 2.02–2.28 (m, 4 H), 2.36–2.44 (m, 1 H),
1
2.62 (dd, J = 14.1, 0.9 Hz, 1 H), 2.97 (dd, J = 14.1,
13
2
.1 Hz, 1 H), 4.11–4.29 (m, 4 H); C NMR (CDCl ), ꢁ
3
2
-(2,2-Dimethylpropyl)-3,3-dimethylcyclopentanone.
13.87, 29.32, 29.92, 30.53, 31.30, 41.68, 45.04, 46.11,
1
The ketone was a solid, m.p. 42–44°C: H NMR
CDCl ), ꢁ 0.71 (s, 3 H), 0.88 (s, 9 H), 0.98 (dd,
57.70, 61.67, 61.71, 170.18, 170.30, 207.52; MS, m/z
‡
(
312.1928 (10) (calculated for M 312.1937), 297 (27),
3
J = 13.8, 1.5 Hz, 1 H), 1.12 (s, 3 H), 1.52 (dd, J = 13.8,
255 (54), 239 (27), 211 (24), 181 (44), 175 (58), 138 (43),
57 (100).
6
1
.9 Hz, 1 H), 1.72–1.82 (m, 3 H), 2.14 (ddd, J = 19.2,
0.8, 8.7 Hz, 1 H), 2.32 (dddd, J = 19.2, 8.4, 3.3, 1.2 Hz, 1
1
3
H); C NMR, ꢁ 21.22, 27.99, 29.45, 30.24, 34.75, 35.54,
3
6.33, 39.55, 57.04, 219.63; MS, m/z 182.1670 (7)
3,3-Bis(ethoxycarbonyl)-8,8-dimethylnonanenitrile
(3c). The material was isolated as a liquid: H NMR
‡
1
(calculated for M 182.1671), 167 (59), 153 (16), 125
66), 111 (53), 70 (40), 57 (100).
(
(CDCl ), ꢁ 0.87 (s, 9 H), 1.15–1.35 (m, 12 H), 2.06–2.12
3
13
(
m, 2 H), 2.95 (s, 2 H), 4.25 (q, J = 7.2 Hz, 4 H);
C
1
-(Cyanomethyl)-4-(2,2-dimethylpropyl)-3-pyrrolidi-
NMR (CDCl ), ꢁ 13.88, 21.72, 24.51, 24.87, 29.24,
3
1
none (1d). The product was isolated as a liquid: H NMR
CDCl ), ꢁ 0.92 (s, 9 H), 1.22 (dd, J = 14.4, 9.6 Hz, 1 H),
30.16, 32.69, 43.66, 55.30, 62.23, 116.31, 168.82; MS, m/
‡
(
z 311.2087 (7) (calculated for M 311.2096), 296 (86),
3
1
.87 (dd, J = 14.1, 2.4 Hz, 1 H), 2.42–2.52 (m, 1 H), 2.59
254 (20), 238 (32), 199 (84), 182 (88), 154 (45), 97 (30),
57 (100).
(
(
dd, J = 9.6, 8.8 Hz, 1 H), 2.91 (d, J = 16.5 Hz, 1 H), 3.36
d, J = 16.5 Hz, 1 H), 3.49 (t, J = 8.1 Hz, 1 H), 3.76 (s, 2
1
3
H); C NMR (CDCl ), ꢁ 29.54, 30.36, 42.12, 42.37,
3
4
6.61, 58.17, 58.21, 113.94, 213.91; MS, m/z 194.1417
2-(2,2-Dimethylpropyl)-4,4-bis(ethoxycarbonyl)cyclo-
hexanone (2d). The compound was isolated as a liquid:
‡
(13) (calculated for M 194.1419), 179 (28), 166 (15),
1
151 (13), 109 (28), 69 (64), 57 (100).
H NMR (CDCl ), ꢁ 0.76 (dd, J = 14.4, 4.5 Hz, 1 H), 0.98
3
(s, 9 H), 1.26 (t, J = 7.2 Hz, 3 H), 1.32 (t, J = 7.2 Hz, 3 H),
2
-(2,2-Dimethylpropyl)-4,4-bis(ethoxycarbonyl)cyclo-
1.87 (t, J = 13.2 Hz, 1 H), 2.11 (dt, J = 13.2, 5.1 Hz, 1 H),
2.25 (dd, J = 14.1, 4.8 Hz, 1 H), 2.37–2.75 (m, 5 H), 4.19
1
pentanone (1e). The product was isolated as a liquid: H
NMR (CDCl ), ꢁ 0.92 (s, 9 H), 1.08 (dd, J = 14.1, 9.3 Hz,
13
(q, J = 7.2 Hz, 2 H), 4.32 (dq, J = 7.2, 2.4 Hz, 2 H);
C
3
1
1
H), 1.28 (t, J = 7.2 Hz, 6 H), 1.92 (dd, J = 14.1, 2.4 Hz,
H), 1.96 (t, J = 12.6 Hz, 1 H), 2.24–2.35 (m, 1 H), 2.73
NMR (CDCl ), ꢁ 13.92, 14.07, 29.27, 30.53, 31.94,
3
38.21, 40.33, 40.67, 43.07, 54.75, 61.72, 170.47, 170.81,
‡
(d, J = 19.2 Hz, 1 H), 2.92–3.05 (m, 2 H), 4.19–4.30 (m, 4
210.06; MS, m/z 312.1941 (18) (calculated for M
1
3
H); C NMR (CDCl ), ꢁ 13.94, 29.67, 30.36, 39.08,
312.1936), 297 (26), 296 (28), 255 (61), 181 (49), 173
(100), 140 (20), 108 (23), 69 (80), 57 (83).
3
4
2
2
4.16, 44.25, 45.32, 55.06, 61.97, 170.75, 171.03,
15.94; MS, m/z 298.1787 (15) (calculated for M
98.1780), 283 (14), 253 (11), 241 (18), 200 (100), 154
‡
(93), 69 (92), 57 (55).
4,4-Bis(ethoxycarbonyl)-8,8-dimethylnonanenitrile
1
(3d). The product was isolated as a liquid: H NMR
8
,8-Dimethylnonanenitrile (3a). The product was iso-
(CDCl ), ꢁ 0.86 (s, 9 H), 1.15–1.26 (m, 4 H), 1.27 (t,
3
1
lated as a liquid: H NMR (CDCl ), ꢁ 0.86 (s, 9 H), 1.12–
J = 7.2 Hz, 6 H), 1.82–1.87 (m, 2 H), 2.22–2.27 (m, 2 H),
3
1
3
13
1.76 (m, 10 H), 2.34 (t, J = 7.5 Hz, 2 H); C NMR
2.38–2.43 (m, 2 H), 4.14–4.28 (m, 4 H); C NMR
(
CDCl ), ꢁ 17.12, 24.22, 25.37, 28.70, 29.36, 29.66,
(CDCl ), ꢁ 13.03, 14.02, 19.13, 28.87, 29.25, 30.31,
3
3
30.25, 44.04, 119.86.
34.14, 44.23, 56.72, 61.60, 119.12, MS, m/z 311.2094 (2)
‡
(calculated for M 311.2097), 296 (35), 266 (16), 254
4-(2,2-Dimethylpropyl)-dihydro-2H-pyran-3-(4H)-one
(19), 181 (17), 173 (100), 108 (25), 57 (61).
(
2
2b). The product was isolated as a liquid: IR (neat),
959, 2869, 1724, 1476, 1367, 483 cm ; H NMR
�
1
1
(
1
CDCl ), ꢁ 0.90 (s, 9 H), 0.94 (dd, J = 14.1, 4.8 Hz, 1 H),
2-(2,2-Dimethylpropyl)-4,4-bis(ethoxycarbonyl)pyrroli-
dine (4). The compound was isolated as a liquid: H
3
1
.76–1.89 (m, 1 H), 2.17–2.28 (m, 2 H), 2.44–2.57 (m, 1
13
H), 3.81–3.98 (m, 2 H), 4.02 (JAB = 20.7 Hz, 2 H);
NMR (CDCl ), ꢁ 29.45, 30.65, 34.34, 41.46, 43.82,
6
M 169.1228), 169 (8), 155 (10), 113 (25), 73 (20), 69
(
C
NMR, ꢁ 0.95 (s, 9 H), 1.26 (t, J = 7.2 Hz, 6 H), 1.41 (dd,
J = 14.1, 6.6 Hz, 1 H), 1.57 (dd, J = 13.8, 5.4 Hz, 1 H),
1.77 (dd, J = 13.5, 9.3 Hz, 1 H), 2.08 (br s, 1 H), 2.67 (dd,
J = 13.2, 6.6 Hz, 1 H), 3.13 (d, J = 12.3 Hz, 1 H), 3.11–
3.21 (m, 1 H), 3.63 (d, J = 12.6 Hz, 1 H), 4.16–4.26 (m, 4
3
6.07, 74.60, 209.35; MS, m/z 169.1224 (calculated for
‡
15), 57 (100).
1
3
H); C NMR (CDCl ), ꢁ 13.97, 13.99, 30.03 (Â2), 43.33,
3
2
-(2,2-Dimethylpropyl)-5,5-bis(ethyoxycarbonyl)cyclo-
49.29, 54.70, 57.73, 61.49 (Â2), 61.57, 171.25, 172.25;
1
‡
hexanone (2c). The material was isolated as a liquid: H
MS, m/z 285.1940 (1) (calculated for M 285.1940), 270
NMR (CDCl ), ꢁ 0.86 (s, 9 H), 1.15–1.32 (m, 7 H), 1.48–
(2), 240 (9), 214 (100), 194 (7), 140 (14), 68 (10).
3

1998 John Wiley & Sons, Ltd.
JOURNAL OF PHYSICAL ORGANIC CHEMISTRY, VOL. 11, 715–721 (1998)

CYCLIZATIONS IN HOMOLYTIC REACTIONS OF UNSATURATED NITRILES WITH t-BuHgX
721
D. Mendenhall, W. Van Hoof and K. U. Ingold. J. Am. Chem. Soc.
6, 6068 (1974).
3. J. Kalvoda. Helv. Chim. Acta 51, 267 (1968); and D. S. Watt. J.
Am. Chem. Soc. 98, 271 (1976); A. L. J. Beckwith, D. M. O’Shea
SUPPLEMENTARY MATERIAL
9
1
Synthesis and spectral properties of precursors employed
(
7 pages) can be found on the epoc website at http://
and S. W. Westwood. J. Am. Chem. Soc. 110, 2565 (1988).
˙
1
4. In the 1,2-rearrangement of p-C(Me)
2
CH
2
the observed rate
www.wiley.com/epoc
�
1
� 1
constants at 25°C are p = CN (0.9 s ) CꢂCCMe
3
(93 s
)
7
� 1
2
CH CH (10 s ); D. Lindsay, J. Lusztyk and K. U. Ingold. J.
Am. Chem. Soc. 106, 7087 (1984).
1
5. G. A. Russell, C.-F. Yao, R. Rajaratnam and B. H. Kim. J. Am.
Chem. Soc. 113, 373 (1991); G. A. Russell, L. Wang and R.
Rajaratnam. J. Org. Chem. 61, 8988 (1996).
Acknowledgments
This work was supported by grants from the National
Science Foundation (CHE-9220639) and the Petroleum
Research Fund (32021-AC4).
16. G. A. Russell, P. Chen, C.-F. Yao and B. H. Kim. J. Am. Chem.
Soc. 117, 5967 (1995).
1
7. 5-Exo cyclization of aminium radical cations also occurs much
more readily than the cyclization of the neutral aminyl radicals: J.
H. Horner, F. N. Martinez, O. M. Musa, M. Newcomb and H. E.
Shahin. J. Am. Chem. Soc. 117 11124 (1995).
1
1
8. B.-W. Yeung, J. L. M. Contelles and B. Fraser-Reid. J. Chem. Soc.,
Chem. Commun. 1160 (1989).
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11, 4921 (1989).
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SnH cyclization is not
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7
8
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(
8
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3
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of 4-pentenyl
radicals,
whereas
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CH
2
CH
2
OCH CH CH
2
2
undergoes 5-exo cyclization ca 40 times
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and C. H. Schiesser. Tetrahedron 41, 3925 (1985).
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7, 7175 (1992).
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1
1
1
(
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Trans. 2 1353 (1979).
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D. Crow, H. McNab and J. M. Philip. Aust. J. Chem. 29, 2299
(1993), and references cited therein.
29. However, reaction of Bu
3
SnH with 4- or 5-iodoalkyl azides or of
(TMS) SiH with the corresponding bromides gives good yields of
3
(
1976).
2. (t-Bu)
C=N undergoes b-elimination of t-Bu with t1/2 ꢄ 0.1 s at
°C, whereas t-BuC(Me)
the cyclized amines, indicating preferential radical attack at the
halogen: S. Kim, G. H. Joe and J. Y. Do. J. Am. Chem. Soc. 116,
5521 (1994).
.
.
2
˙
� 9
0
2
CO has t1/2 = 1 Â 10 s; D. Griller, G.

1998 John Wiley & Sons, Ltd.
JOURNAL OF PHYSICAL ORGANIC CHEMISTRY, VOL. 11, 715–721 (1998)