Photoinduced, ionic Meerwein arylation of olefins

Article abstract of DOI:10.1021/jo010469s

Irradiation of 4-chloroaniline or of its N,N-dimethyl derivative in polar solvents generates the corresponding triplet phenyl cations. These are trapped by alkenes yielding arylated products in medium to good yields. B3LYP calculations show that the triplet cation slides with negligible activation energy to a bonded adduct with ethylene, whereas it forms only a marginally stabilized CT complex with water (chosen as a representative σ nucleophile). The structure of the final products depends on the preferred path from the adduct cation with the alkene. In the case of aryl olefins, this deprotonates to stilbene derivatives, while, from 2,3-dimethyl-2-butene and allytrimethylsilane, allylanilines are obtained by elimination of an electrofugal group in γ. In the case of mono- and disubstituted alkenes the cation adds chloride rather than eliminating and β-chloroalkylanilines are obtained. The regio- and sterochemistry of the addition across the alkene are best understood with a phenonium ion structure for the adduct. The nucleophile entering in fi can be varied under conditions in which the adduct cation is trapped more efficiently than the starting phenyl cation. Thus, β-methoxyalkylanilines are formed when the irradiation is carried out in methanol. β-Iodoalkylanilines are obtained in acetonitrile containing iodide and unsubstituted alkylanilines in the presence of sodium borohydride. A case of intramolecular nucleophilic trapping is found with 4-pentenoic acid. The reaction is a wide-scope ionic analogue of the radicalic Meerwin arylation of olefins.

Full text of DOI:10.1021/jo010469s

6344
J . Org. Chem. 2001, 66, 6344-6352
P h otoin d u ced , Ion ic Meer w ein Ar yla tion of Olefin s
Mariella Mella, Paolo Coppo, Benedetta Guizzardi, Maurizio Fagnoni, Mauro Freccero, and
Angelo Albini*
Department of Organic Chemistry, University of Pavia, Via Taramelli 10, 27100 Pavia, Italy
albini@chifis.unipv.it
Received May 7, 2001
Irradiation of 4-chloroaniline or of its N,N-dimethyl derivative in polar solvents generates the
corresponding triplet phenyl cations. These are trapped by alkenes yielding arylated products in
medium to good yields. B3LYP calculations show that the triplet cation slides with negligible
activation energy to a bonded adduct with ethylene, whereas it forms only a marginally stabilized
CT complex with water (chosen as a representative σ nucleophile). The structure of the final products
depends on the preferred path from the adduct cation with the alkene. In the case of aryl olefins,
this deprotonates to stilbene derivatives, while, from 2,3-dimethyl-2-butene and allytrimethylsilane,
allylanilines are obtained by elimination of an electrofugal group in γ. In the case of mono- and
disubstituted alkenes the cation adds chloride rather than eliminating and â-chloroalkylanilines
are obtained. The regio- and sterochemistry of the addition across the alkene are best understood
with a phenonium ion structure for the adduct. The nucleophile entering in â can be varied under
conditions in which the adduct cation is trapped more efficiently than the starting phenyl cation.
Thus, â-methoxyalkylanilines are formed when the irradiation is carried out in methanol.
â-Iodoalkylanilines are obtained in acetonitrile containing iodide and unsubstituted alkylanilines
in the presence of sodium borohydride. A case of intramolecular nucleophilic trapping is found
with 4-pentenoic acid. The reaction is a wide-scope ionic analogue of the radicalic Meerwin arylation
of olefins.
The Meerwein arylation of alkenes1 involves reduction
of diazonium salts, homolytic dediazonation, and addition
of the resulting aryl radical onto an olefin activated by
an electron-withdrawing group.2 This is shown in Scheme
1, path a, for a typical example in which the initial
reductive step involves a Cu(I) species and the process
is terminated by ligand transfer from copper(II) chloride.
The process was first proposed to involve heterolytic
cleavage (path b)1 but was subsequently proved to follow
the homolytic path.3 Thus the phenyl radical, not the
cation, is involved in the C-C bond-forming step. The
latter species has been generated by photolysis of phen-
yldiazonium salts,4 but under these conditions only
synthetically uninteresting reactions with the solvent
(acting as a nucleophile or as a hydrogen donor) have
been reported.4 In fact, C-C bond formation via an aryl
cation was not known until recently. In 1998, however,
it was reported that phenyl cations formed via photoin-
duced dediazonization could be trapped by arenes,5,6 and
in the following year, we found a different access to such
Sch em e 1
cations, on the basis of the photoinduced heterolysis of
4-chloroanilline and its N,N-dimethyl derivative. These
gave the corresponding 4-aminophenyl cations (Scheme
1, path c), which could be trapped by arenes.7 This
suggested the possibility of a ionic analogue of the
Meerwein reaction. As it appears in the following, the
expectation was fulfilled and led to an arylation reaction
susceptible to several variations of synthetic interest.8
Indeed, this photochemical method for the generation of
phenyl cations showed a limited dependence on experi-
mental parameters and allowed more freedom in direct-
ing the ensuing chemistry of such intermediates through
the appropriate change in the conditions. Furthermore,
B3LYP calculations on the triplet 4-aminophenyl cation
allowed one to rationalize the mechanism of the addition
to alkene as well as the lack of reaction of this cation
with neutral σ nucleophiles.
* Corresponding author. Fax: 39-0382-507323.
(1) Meerwein, H.; Buchner, E.; van Emster, K. J . Prakt. Chem. 1939,
152, 237.
(2) Rondestvedt, C. S. Org. React. 1960, 11, 189. Rondestvedt, C. S.
Org. React. 1976, 24, 222. Ghosez, A.; Giese, B.; Zipse, H. In Methoden
der organischen Chemie; Regitz, M., Giese, B., Eds.; Thieme: Stuttgart,
Germany, 1989; Vol. E19a, p 1197. Galli, C. Chem. Rev. 1988, 88, 765.
Oae, S.; Shinkama, K.; Kim, Y. H. Bull. Chem. Soc. J pn. 1980, 53,
1065. Citterio, A.; Minisci, F.; Vismara, E. J . Org. Chem. 1982, 47, 81.
(3) Kochi, J . K. J . Am. Chem. Soc. 1955, 77, 5090. Kochi, J . K. J .
Am. Chem. Soc. 1955, 77, 5274.
(4) Stang, P. J . In Dicordinate Carbocations; Rappoport, Z., Stang,
P. J ., Eds.; Wiley: New York, 1997; p 461. (b) Hanack, M.; Subrama-
nian, L. R. In Methoden der organischen Chemie; Hanck, M., Ed.;
Thieme: Stuttgart, Germany, 1990; Vol. E19C, p 249. Zollinger, H.
Diazochemistry I; VCH: New York, 1995. (b) Gasper, S. M.; Devadoss,
C.; Schuster, G. B. J . Am. Chem. Soc. 1995, 117, 5206.
(5) Steenken, S.; Askokkuna, M.; Maruthamuthu, P.; McClelland,
R. A. J . Am. Chem. Soc. 1998, 120, 11925.
(6) This differs from the Gomberg-Bachmann arylation of aromatic
compounds, which again involves aryl radicals and not cations; see
ref 2.
(7) See the accompanying manuscript.
(8) Preliminary communication of part of this work: Fagnoni, M.;
Mella, M.; Albini, A. Org. Lett. 1999, 1, 1299. Coppo, P.; Fagnoni, M.;
Albini, A. Tetrahedron Lett. 2001, 42, 4271.
10.1021/jo010469s CCC: $20.00 © 2001 American Chemical Society
Published on Web 08/24/2001

Photoinduced, Ionic Meerwein Arylation of Olefins
J . Org. Chem., Vol. 66, No. 19, 2001 6345
Sch em e 2
Sch em e 3
nonmethylated chloroaniline 1b was similarly alkylated
in the presence of 4 with practically the same yields.
Irradiation of both chloroanilines in the presence of 2,3-
dimethyl-2-butene (7) gave reasonable yields of chlorine-
free products, the trimethylallylanilines 8a ,b (64 and
55%, respectively). The reaction with cyclopentene (9) and
cyclohexene (11) gave again â-chloroalkylanilines (10,
12). Yields were lower in these cases (42-49%), and the
products were formed in the trans configuration.
1,1-Diphenylethene (13) was then tested as a repre-
sentative aromatic alkene. This was used at a lower
concentration (0.1 M) and slowed the photoreaction of 1a
because of competitive absorption in the same wave-
length range. It gave a good yield (90%) of the (ami-
nophenyl)diphenylethene 14a .
The photochemical reaction was then explored in the
presence of functionalized alkenes. Allyltrimethylsilane
(15) was a quite efficient trap giving the allylaniline 16a
(81%). 4-Pentenoic acid (17) gave lactone 18 in 70% yield.
With enol ether 19 extensive polymerization took place
due to catalysis by the hydrochloric acid liberated in the
photodecomposition of 1a . However, stirring solid potas-
sium carbonate in the irradiation vessel during the
reaction eliminated this drawback, and under this condi-
tion, the aniline was alkylated, giving after chromatog-
raphy lactol 20a , obtained as a solid (49%; in solution
this hemiacetal was present as a mixture of diastereo-
isomers).
Ta ble 1. P r ep a r a tion of 4-Alk yla n ilin es by Ir r a d ia tion of
Ch lor oa n ilin es 1a ,b in Aceton itr ile in th e P r esen ce of
Alk en es
alkenea
(1 M)
alkylated
aniline
other products
(% yield)b
aniline
1a
1b
1a
1b
1b
1a
1b
1a
1a
1a
1a
4
4
7
7
9
11
11
13c
15
17
19
5a (35), 6a (18)
5b (35), 6b (16)
8a (64)
8b (55)
10b (49)
12a (42)
12b (45)
14a (90)
16a (81)
2a (20)
2b (23)
2a (15)
2b (18)
2b (29)
2a (34)
2b (37)
2a (3)
2a (4)
2a (5)
2a (13)
18a (70)
20a (49)
a
b
1 M except when noted. In all cases low amounts (up to 5%)
of diphenyldiamines 3a ,b were formed. c 0.1 M.
Resu lts
Solven t E ffect a n d Qu a n t u m Yield Mea su r e-
m en ts. The above photochemical reaction of the anilines
with alkenes was explored also in other solvents using
1-hexene. Alkylation was successful also under these
conditions, but several changes occurred. These included
the following: (i) a change in the structure of the
alkylated products, since the irradiation in methanol gave
the â-methoxyalkylaniline 21, with a trace of isomeric
22 detected only by GC/MS, rather than the two isomeric
â-chloroalkylanilines discussed above (see Scheme 3,
Table 3); (ii) a variation in the ratio between alkylanilines
and other products, in particular reduced anilines 2
(Table 2); (iii) a change in the reaction quantum yield
(Table 2); (iv) the formation of additional products when
the solvent was itself a trap for the phenyl cation, as it
was the case for benzene which gave some biphenylamine
(Table 2).
P r ep a r a tive Ir r a d ia tion s in Aceton itr ile. In the
accompanying paper it has been reported that the ir-
radiation of 4-chloroanilines 1a ,b in acetonitrile caused
both reductive dechlorination to the corresponding anilines
2a ,b and coupling to the biphenyldiamines 3a ,b (see
Scheme 2).7 The photochemical reaction was now ex-
plored in the presence of alkenes. Thus, a solution
containing 0.05 M 1a and 1 M 1-hexene (4) was irradiated
and it was observed that the photodecomposition of the
chloroanilines occurred at about the same rate as in neat
MeCN, but the yields of aniline 2a and of 3a dropped to
20 and 5%, respectively, and two new products were
formed. These were characterized as the regioisomeric
4-(â-chloroalkyl)anilines 5a and 6a , formed in 35% and
18% yields, respectively (Scheme 2, Table 1). In the
presence of a lower amount of the alkene, e.g. 0.1 M, the
main products remained 2a and 3a with no preparatively
significant formation of the alkylanilines 5a and 6a . The
Preparative studies were not extended to all conditions,
but points ii and iii were investigated systematically by

6346 J . Org. Chem., Vol. 66, No. 19, 2001
Mella et al.
Ta ble 2. Rea ction Qu a n tu m Yield a n d P er cen ta ges of Red u ction a n d Alk yla tion in th e Ir r a d ia tion of Ch lor oa n ilin es
1a ,b in Va r iou s Solven ts in th e P r esen ce of 1 M 1-Hexen e
1a
1b
solvent
MeCN
Φr
% redn
% alkyln
% diamine
Φr
% redn
% alkylna
0.84
0.94
0.55
0.91
0.68
0.45
0.05
11
26
6
68
11
11
70
60
72
21
80
55
40b
7
9
12
4
4
5
0.44
0.47
0.2
0.39
0.23
0.11
0.05
11
21
9
60
8
86
76
85
35
84
80
58c
MeOH
CF3CH2OH
iso-PrOH
tert-BuOH
AcOEt
13
benzene
a
b
A small amount of diphenyldiamine 3b (up to 5%) is formed also in these cases. 35% of N,N-dimethyl-4-biphenylamine also formed.
c 25% of 4-biphenylamine also formed.
Ta ble 3. P r od u cts fr om th e Ir r a d ia tion of
4-ch lor oa n ilin es 1a ,b in th e P r esen ce of Alk en es (1 M)
u n d er Va r iou s Con d ition sa
Sch em e 4
reagentsb
conditions
products (% yield)
1a , 4
1b, 4
1a , 4
MeOH
2a (15), 21a (58), 22a (tr)
2b (12), 21b (62), 22b (tr)
MeOHb
MeCN, 0.015 M NaIc 2a (2), 23a (35), 24a (5),
4-IC6H4NMe2 (10)
1b, 4
1a , 4
1b, 4
MeCN, 0.015 M NaIc 2b (3), 23 (32), 24 (10),
4-IC6H4NH2 (12)
2a (33), 5a (tr), 6a (tr), 25a (32),
26a (21)
2b (27), 5b (2), 6b (3), 25b (34),
26b (17)
2b (36), 10 (8), 27 (38)
2b (36), 12 (7), 28 (33)
d
MeCN, NaBH4
MeCN, NaBH4
d
d
d
1b, 9
1b, 11
MeCN, NaBH4
MeCN, NaBH4
a
b
g85% conversion except where otherwise noted. 0.05 M 1a ,b
except where otherwise noted. c 0.02 M 1b, 60% conversion.
A
d
concentrated aqueous solution of NaBH4/K2CO3 was drop-by-drop
added during the irradiation (see Experimental Section).
measuring the reaction quantum yield of reaction of
chloroanilines 1a ,b (Φr) and the proportions of reduction
to anilines 2a ,b vs that of alkylation in a range of
solvents. The results are reported in Table 2.
hexylanilines 5 and 6 in the presence of NaBH4/K2CO3
did not cause their reduction.
The hexylanilines 25 and 26 were easily freed from the
nonalkylated anilines by bulb-to-bulb distillation, and
this appeared to be a viable entry to such compounds.
Therefore, the experiments were extended to cycloalkenes
9 and 11 and reasonable yields of the 4-cycloalkylanilines
27 and 28 were obtained. In these experiments, as well
as in the previous cases, the rate of photochemical
reaction of the chloroanilines underwent no major change
with respect to the irradiation in a neat solvent, although,
as seen above, the product distribution changed deeply.
The reaction of 1b in MeCN containing 0.03 M NaBH4
was somewhat more efficient than in neat MeCN (Φr ca.
0.6 vs 0.44) both in the presence and in the absence of
the olefins. There was no corresponding increase in the
case of 1a .
Ca lcu la tion s. In the accompanying paper it has been
shown that photoheterolysis of chloroanilines 1a ,b led
to the corresponding triplet phenyl cations (29), which is
suggested to be the key intermediate in the present
reactions (see Scheme 4).7 This state had an intermediate
carbene-diradical at C1, as evidenced by computational
data obtained at the B3LYP/6-31G(d) as well CASSCF-
(8,8)/6-31(d) levels of theory. To obtain a mechanistic
rationale for the chemistry discussed above, viz. the
efficient arylation of alkene as contrasted with the lack
of formation of ethers with alcohols, a computational
study was carried out. Thus, the PESs (potential energy
surfaces) of the 4-aminophenyl cation (both triplet and
singlet states) with water and with ethylene (chosen as
prototypes of an n nucleophile and π nucleophile, respec-
tively) were investigated in the gas phase. Since our
previous work had demonstrated that the B3LYP method
Tr a p p in g by An ion s. A previous study7 had shown
that irradiation of the anilines in the presence of iodide
led to the corresponding iodoanilines. In view of the
present finding that â-chloroalkylanilines were formed
in the presence of alkenes, it was explored whether iodide
could be incorporated in the alkyl chain. Indeed, irradia-
tion of 0.02 M solution of 1a ,b containing 0.015 M sodium
iodide and 1-hexene gave the â-iodoalkylanilines 23 and
24 as the main products at 60% conversion (Scheme 3,
Table 3), though at complete conversion some secondary
decomposition occurred.
This encouraged us to extend the experiments to
conditions devised to modify the nucleophile entering in
the â position during the process. The most significant
target appeared to be insertion of a nonfunctionalized
alkyl chain. A relatively mild reducing agent was used,
NaBH4. This was soluble up to 0.03 M in MeCN.
Irradiation of chloroanilines 1a ,b under this condition
caused almost only reductive dechlorination (93-95%).
In the presence of alkenes, however, both anilines and
alkylanilines were formed, with a strong reduction of the
proportion of the â-chloroanilines. From the preparative
point of view, it was found more expedient to drop-by-
drop add a concentrated solution of NaBH4/K2CO3 during
the irradiation to maintain a low steady-state concentra-
tion of the reducing agent. Under these conditions the
hexylanilines 25a ,b and 26a ,b were obtained from both
1a ,b in 50-55% combined yield along with ca. 30%
reduced anilines 2a ,b and e5% chloroalkylanilines (5,
6). In a control experiment, it was shown that irradiation
under the same conditions of a solution of the â-chloro-

Photoinduced, Ionic Meerwein Arylation of Olefins
J . Org. Chem., Vol. 66, No. 19, 2001 6347
the minima located were 333 in the triplet and 341 on
the singlet surface.
Sch em e 5. P oten tia l En er gy Su r fa ce (B3LYP /
6-31G(d )) for Sin glet (1A′) a n d Tr ip let (3B2) Sta tes
of th e 4-Am in op h en yl Ca tion w ith Eth ylen e
Discu ssion
Ma in F ea tu r es a n d Scop e of th e Rea ction . A
parallel mechanistic investigation of the photochemistry
of 4-chloroanilines 1a ,b7 demonstrated that these un-
dergo heterolytic cleavage from the triplet state and give
the corresponding phenyl cations. These are formed in
the triplet state that in this case (contrary to parent
phenyl cation) are the ground states (stabilized by >10
kcal mol-1 with respect to the singlet). Such species are
trapped by benzene and its methyl derivatives through
an electrophilic substitution reaction, but do not form
ethers with alcohols.7 Ethers are on the contrary obtained
by photodecomposition of 4-(dialkylamino)phenyldiazo-
nium salts in alcohols, a reaction presumed to involve
the singlet phenyl cation.4d
The present study confirms the expectation based on
the above-mentioned indications about the reactivity of
triplet cation, demonstrating that electrophilic addition
to alkenes occurs efficiently and that the choice of the
medium and of additives allows one to further manipu-
late the path followed toward a variety of final products.
The irradiation of choroanilines in the presence of alkenes
can thus be developed into a versatile method for the
synthesis of variously functionalized alkylanilines.
Consideration of the quantum yields of reactions of the
chloroanilines in the presence of alkenes (Φr in Table 2)
shows that these little differ from those previously
measured in the same solvents in their absence (compare
ref 7).9 This implies that a reactive intermediate is
formed upon excitation independently from the additives
but with a strongly polarity-dependent efficiency. This
is the 4-aminophenyl cation 29, formed, as previously
proposed,7 from the heterolysis of triplet chloroanilines
1. The cleavage is due to the internal charge-transfer
character of these states and is promoted by a polar
medium, as shown by the increase by a factor of 20 in
passing from benzene to acetonitrile and alcohols with
ethyl acetate in an intermediate position. A more acidic
alcohol, on the other hand, depresses Φr (see the lower
values with CF3CH2OH), since in this case hydrogen
bonding of the amino group decreases the CT character
of the excited state.
Sch em e 6. P oten tia l En er gy Su r fa ce (B3LYP /
6-31G(d )) for Sin glet (1A′) a n d Tr ip let (3B2) Sta tes
of th e 4-Am in op h en yl Ca tion w ith Wa ter
As surmised, the cation is trapped by alkenes. That
the alkene traps the cation rather than interacting with
triplet chloroaniline before the fast fragmentation of the
latter (τ , 100 ns)7 is indicated by the above-mentioned
invariance of Φr in the absence and in the presence of
the alkenes which, along with the further evidence below,
excludes that a different mechanism, such as photoin-
duced electron transfer, exciplex formation or SRN1, is
involved. End products are vinyl-, allyl- or â-chloroalkyl-
anilines, all of which can be rationalized as arising via
the intermediate adduct cation. As it will be discussed
was satisfactory for describing the nature of the triplet
state of this cation,7 this method (with a 6-31G(d) basis
set) could be confidently used for locating possible
intermediates on the PES in the case of the triplet. In
the case of the singlet state, one had to keep in mind that,
due to the peculiar nature of the singlet state which is
described by two electronic configurations (π6σ0 and π4σ2),
a better strategy for a computational investigation on the
singlet state reactivity would be using a multiconfigu-
rational approach (CASSCF method). Work is in progress
on this issue. However, at the present stage B3LYP data
are sufficient for evidencing the contrasting behavior of
the two states as far as the location of the intermediates
along the PES is concerned.
(9) (a) An exception is the reaction with 1,1-diphenylethylene, where
competitive light absorption by the alkene makes it difficult to evaluate
the quantum yield of the reaction via excited chloroaniline and its
quantum yield. A recent investigation by Arnold9b reports a large
number of photoreactions of this alkene with substituted halobenzenes,
including methoxychlorobenzenes. Such reaction apparently involve
an electron-transfer path or an exciplex. A donating group does not
favor that reaction, and we feel that this mechanism does not apply
in the present reaction of chloroanilines. (b) Mangion, D.; Arnold, D.
R. Can. J . Chem. 1999, 77, 1655.
The results are shown in Scheme 5 for the reaction
with ethylene, where two minima were located on the
triplet PES (303 and 313) and one on the singlet PES
(321), and in Scheme 6 for the reaction with water, where

6348 J . Org. Chem., Vol. 66, No. 19, 2001
Mella et al.
Sch em e 7
in the following, this can be envisaged either as an open-
chain or as a phenonium cation (respectively structures
30 and 32 in Scheme 4). Evidence for the structure of
such an intermediate and a rationalization of its role in
the formation of the final products are presented.
R ea ct ion s of t h e P h en yl Ca t ion . The PES of the
reaction between both the triplet (293, 3B2 symmetry) and
1
the singlet (291, A′ symmetry) states of 4-aminophenyl
cation with ethylene (in the gas phase) are depicted in
Scheme 5. Both states evolve to further intermediates
(30-32 and respectively 33 and 34) with a negligible
electronic energy barrier. The PES appear to be slippery
surfaces, and any attempt for locating transition struc-
tures connecting the reactants to such intermediates
failed. On the other hand, the fact that the activation
energy barrier is negligible in the present process, where
the 4-aminophenyl cation cleaves no σ bond, comes as
no surprise when one considers that for the parent phenyl
cation it has been found that hydride anion abstraction
from an alkyl C-H group occurs with a very small (1.2
kcal mol-1) electronic activation energy.11
A negligible energy barrier favors the chemical reaction
pathway with respect to ISC from triplet 293 to singlet
291. This requires at least 9.1 kcal mol-1, as suggested
by the reported computation of the energy difference
between the triplet state and the MECP (minimum
energy crossing point, between triplet and singlet PESs).12
Thus, it is reasonable that the 4-aminophenyl cation
when generated, as in the present case, in the triplet
state, reacts maintaining this multiplicity.
Two minima were located on the triplet PES surface
in the reaction with ethylene, viz. cations 303 and 313
(see Scheme 5). The latter intermediate has a symmetric
spirocyclopropane structure with a delocalized diradical
character and the charge likewise delocalized, whereas
the latter one is an open-chain structure with a localized
alkyl radical character and the aromatic ring as a π
radical-cation. 313 is only 10.6 kcal mol-1 more stable
than the reactants, but 303, which shows a completely
formed C1-CR bond, lies much more below the reactants
(by 43.7 kcal mol-1). Cation 303 is the most stable open-
shell species and is expected to control the reaction of
triplet 4-aminophenyl cation with ethylene. This theo-
retical evidence suggests that it should be possible (at
least in an N,N-dialkylamino derivative of the phenyl
cation) to detect such as intermediate by laser flash
photolysis and predicts that its spectrum should be quite
similar to an N,N-dialkyl-substituted aniline radical
cation. However, the overlap of several intermediates in
flash photolysis discouraged for the moment a detailed
interpretation.
oxygen atom is strongly bonded to C1 (bond length, 1.50
Å), recognizable as 4-aminophenol protonated at the
oxygen atom. This is stabilized by 32.8 kcal mol-1 with
respect to the reagents.
We were unable to find evidence for a comparable σ
intermediate on the triplet PES. However, a CT complex
(333) was located also in this case, a bare 11 kcal mol-1
below the reagents.13 We define this intermediate a “CT
complex” due to very elongated C2-O and C3-O bonds
(3.19 and 3.04 Å, respectively). The fact that the CT
complex lies in a very shallow minimum suggests that
the process is reversible and is not a chemical pathway
leading to the end products in the reaction of the triplet
state with water.
The strikingly different reactivity of singlet and triplet
4-aminophenyl cations discussed above confirm the pic-
ture we gave for these species on the basis of CASSCF-
(8,8)76-31G(d) results. The triplet has a radical-triplet
carbene character well in accord with attack to π nucleo-
philes, whereas the σ cation-singlet carbene character
of the singlet explains the reaction with σ nucleophiles.
Finally, it should be remarked that the reactions of
4-chloroaniline 1b closely parallel those of the N,N-
dimethyl derivative 1a . Therefore, all of the present
reactions take place via the phenyl cation 29 and do not
require previous deprotonation to a neutral carbene 29′
which could be formed only from 1b. In contrast, previous
studies on chlorophenol and chloroaniline, mainly in
water, had considered deprotonation as immediately
following chloride loss, so that the key intermediate was
the neutral carbene.14
Rea ction s of th e Ad d u ct Ca tion s. The formation of
the end products depends on the alkene structure, and
this dependence can be rationalized by considering the
paths from adduct cation. With some of the olefins,
elimination reactions occurs, and these can be rational-
ized through the open-chain intermediate 30 (Scheme 4).
Thus, in the case of diphenylethylene (13) a benzyl cation
(35) is formed and undergoes, as one may expect, proton
loss from the initially attacked position and gives highly
conjugated triphenylethylene (14) (see Scheme 7 and
As for the singlet cation-ethylene system, this evolves
to a cationic closed-shell intermediate (321) which is
similar in structure to high-energy 313 but is the most
stable of all the adduct cations lying 92.0 kcal mol-1 below
the reagents.
The PES of the same cations with water are depicted
in Scheme 6. The singlet state evolves with no significant
energy barrier into a σ intermediate (341), where the
(13) However, exploration of PES of the triplet state of the parent
phenyl cation and water enabled us to locate both a σ-intermediate
similar to 341, which lay 14.6 kcal mol-1 above the reagents, and a CT
complex which was slightly more stable than the reagents. Thus, also
in the case of parent phenyl cation, formation of an adduct where the
oxygen is σ-bonded to the phenyl cation is not energetically favored
for the triplet. Computational and experimental findings on this topic
will be reported in due course.
(10) Traylor, T. G.; Hanstein, W.; Berwin, H. J .; Clinton, N. A.;
Brown, R. S. J . Am. Chem. Soc. 1971, 93, 5715. J arvie, A. W. P.; Holt,
A.; Thompson, J . J . Chem. Soc. B 1969, 852.
(11) Hory, K.; Sonoda, T.; Harada, M.; Yamanaki-Nishida, S.
Tetrahedron 2000, 56, 1429.
(12) Aschi, M.; Harvey, J . N. J . Chem. Soc., Perkin Trans. 2 1999,
1059.
(14) Grabner, G.; Richard, C.; Ko¨hler, G. J . Am. Chem. Soc. 1994,
116, 11470. Durand, A. P.; Brown, R. G.; Worral, D.; Wilkinson, F. J .
Chem. Soc., Perkin Trans. 2 1998, 365. Othmen, K.; Boule, P.;
Szczepanik, B.; Rotkiewicz, K. J . Phys. Chem. A 2000, 104, 9525

Photoinduced, Ionic Meerwein Arylation of Olefins
J . Org. Chem., Vol. 66, No. 19, 2001 6349
Sch em e 8
Sch em e 9
Sch em e 10
formed from enol ether 19 does not eliminate and gives
hemiacetal 20, apparently resulting from addition of
moisture present in the solvent to the cation (see Schemes
2 and 8, path c, Nu ) OH).
Syn th etic Va r ia tion s. The key features of the present
reaction are that the initial triplet phenyl cation formed
by photoheterolysis of the chloroaniline (293; see Scheme
5) has no cationic character at C1 and does not react with
σ nucleophiles, whereas the adduct cation formed with
alkenes, whether having a open-chain structure or that
of a phenoniun ion (30 and respectively 32 in Scheme 8)
does react with σ nucleophiles, charged (Cl-) or un-
charged (MeOH). This allows for a considerable degree
of synthetic variations, since, in the presence of a high
enough concentration of the alkene, trapping of the
4-aminophenyl cation 29 occurs undisturbed by the
additive present, which may however effectively trap the
adduct cation, therefore offering a method for choosing
the group entering in â (path c in Scheme 8).
Thus, a direct entry to â-alkoxyanilines is available by
simply carrying out the irradiation in alcohols, where,
as previously mentioned, no alkoxyanilines (expected
from the trapping of the phenyl cation) are formed. In
methanol, products 21 and 22 are formed with incorpora-
tion of the solvent (see Scheme 8, path e). As mentioned
above, this is accompanied by a much increased bias
toward the Markovnikov product, consistently with the
formulation of the adduct cation as phenonium ion 32.
An intramolecular version of nucleophilic trapping is that
observed with pentenoic acid, where cation 38 undergoes
ring closure by attack of the carboxylic group and gives
the observed lactone 18 (Scheme 10).
path a in Scheme 4). In the case of tertiary alkyl cation
36 deprotonation is only possible from the terminal
position and gives the allylaniline 8. With the â-silyl
cation 37 (where the silicon atom â-stabilization is
operating),10 elimination of a good electrofugal group such
as the trimethylsilyl cation is preferred to formation of
a
phen-
ylalkene by proton loss and gives allylaniline 16 (Scheme
7 and path b in Scheme 4). All of these paths involve
elimination of a good electrofugal group, strengthening
the notion that the entire reaction evolves via cationic
intermediates, even if strongly delocalized.
Nucleophile addition to the adduct cation is the pre-
dominating process with other substrates. This is the case
with less stabilized alkyl cation such as the primary or
secondary cations arising from 1-hexene, cyclopentene,
and cyclohexene (see path c in both Schemes 4 and 8,
Nu- ) Cl-). In these cases, elimination is not competitive
and chloride addition leads to the observed â-chloroalkyl-
anilines. Scheme 5 indicates that the open-chain cation
303 is first formed from triplet phenyl cation. However,
it is possible that this open-shell species undergoes
intersystem crossing to a closed-shell species before
further reacting. Scheme 5 indeed shows that a strongly
stabilized singlet cation is available, viz. phenonium ion
321. Thus it is likely that, unless a very fast different
process competes, structure 32 is achieved. This inter-
mediate is well suited for explaining some features of the
reactions by attributing the regio- and stereoselectivity
observed in the final products to the nucleophile attack
to the phenonium ion rather than to the previous attack
of the phenyl cation to the alkene. In particular the trans
structure of the adducts from cyclic alkenes (10 and 12,
R′-R′′′ ) (CH2)3, 4 in Scheme 9) is well explained on this
basis, as is the fact that only a moderate Markovnikov
regioselectivity is observed with 1-hexene (preferred
attack for R′ ) H, R′′′ ) C4H9; see Scheme 9) when the
entering nucleophile is highly reactive chloride, whereas
the selectivity is much stronger with a weaker nucleo-
phile such as methanol (the ratio 5/6 is 2 to 1, while the
ratio 21/22 is 95 to 5).15
The above results encouraged us to test the versatility
of the method by introducing further functionalities in
the entering alkyl group by the appropriately directing
the nucleophile trapping of the adduct cation. In par-
ticular, the use of charged nucleophiles was appealing
but presented the problem that in this case direct
reaction of phenyl cation with the nucleophile according
to path d was efficient (see Scheme 8). As an example,
irradiation of chloroanilines in acetonitrile containing
sodium iodide or sodium borohydride gave iodoanilines
(15) (a) We are highly indepted to a reviewer for pointing out the
implication of the phenonium pathway. (b) For indications about the
phenonium path, see: Lancelot, C. J .; Schleyer, P. v. R J . Am. Chem.
Soc. 1969, 91, 4291. Lancelot, C. J .; Hayer, I. J .; Schleyer, P. v. R. J .
Am. Chem. Soc. 1969, 91, 4294. Schleyer, P. v. R.; Lancelot, C. J . J .
Am. Chem. Soc. 1969, 91, 4297. Diaz, A. F.; Winstein, S. J . Am. Chem.
Soc. 1969, 91, 4300.
On the other hand, the strongly stabilized cation

6350 J . Org. Chem., Vol. 66, No. 19, 2001
Mella et al.
or respectively anilines in an almost quantitative yield
through direct trapping of 29. To our delight, we found
however that when a low concentration of the nucleophile
was used, phenyl cation 29 was still trapped by 1 M
alkene with a reasonable efficiency and thus â-iodoalkyl-
as well as alkylanilines could be obtained in a decent
yield through nucleophile trapping of 30-32 (paths f and
g, Scheme 8).
Exp er im en ta l Section
Gen er a l Meth od s. N,N-dimethyl-4-chloroaniline (1a , pre-
pared by methylation of aniline 1b) and the other reagents
(of commercial origin) were distilled or recrystallized before
use. For the irradiations, spectroscopic grade solvents were
used as received.
P r ep a r a tive Ir r a d ia tion s in Nea t Solven t. In a typical
experiment a solution of 780 mg of aniline 1a or 625 mg of
aniline 1b (0.05 M) in 100 mL of acetonitrile or in methanol
was irradiated for 1.5 or 3 h in an immersion well apparatus
fitted with an high-pressure mercury arc (125 W, water-cooled
through a quartz jacket) after 15 min of flushing with argon
and maintaining a slow gas flux during the irradiation. With
acid-sensitive substrates (in particular in the experiments with
the nonmethylated aniline 1b) anhydrous potassium carbonate
(2 g) was added and the solution magnetically stirred during
the experiment. In an alternative procedure, irradiations were
carried out by using 20 mL portions of the same solutions in
a number of quartz tubes which were capped after flushing
with argon for 15 min and externally irradiated by means of
6 × 15 W phosphor-coated lamps for 3 or 6 h in a merry-go-
round apparatus. In this case, the solution was made 0.1 M
in triethylamine when buffering the acidity was desired.
Experiments in methanol were similarly carried out. The
progress of the reaction was monitored by GC and GC/MS.
Experiments in the presence of the various alkenes listed in
Table 1 were carried out in the same way.
P r od u cts Isola tion a n d Id en tifica tion . The irradiated
solution was evaporated under reduced pressure and the
residue chromatographed on silica gel 60 HR (Millipore) by
eluting with cyclohexane-ethyl acetate mixtures. The products
were obtained as solids or oils from the fractions (by repeating
the chromatography in the case of unsatisfactory separation)
and characterized by elemental analysis, GC/MS, and NMR
as detailed in the following. The structures of new compounds
were deduced from the results of 1H, 13C, DEPT-135, and 2D-
correlated experiments. Triphenylethylene 14a ,12 allylaniline
16a ,13 and cyclohexylaniline 28b14 have been previously
reported and fully characterized. NMR and GC/MS data are
listed also for compounds previously incompletely character-
ized.
N,N-Dim eth yl-4-(2-ch lor oh exyl)a n ilin e (5a ) a n d N,N-
d im eth yl-4-(1-(ch lor om eth yl)p en tyl)a n ilin e (6a ) were ob-
tained as a mixture (oil), to which the NMR characterization
is referred. Satisfactory separation and characterization was
obtained by GC/MS. Anal. Found: C, 70.22; H, 9.32; N, 5.74.
Calcd for C14H22NCl: C, 70.13; H, 9.25; N, 5.84. 5a : 1H NMR
δ (CDCl3) 0.9 (t, 3H, J ) 7 Hz), 1.3-1.6 (m, 6H), 2.9 (s, 6H),
2.95 (AB part of an ABX system, 2H), 4.0 (X part, 1H), 6.75
and 7.05 (AA′BB′, 4H); 13C NMR δ (CDCl3) 13.9 (CH3), 22.1
(CH2), 28.5 (CH2), 37.0 (CH2), 40.5 (NCH3), 44.1 (CH2), 64.6
(CH-Cl), 112.5 (CH), 129.9 (CH), 132.1, 149.3; GC/MS m/z 239
(18, Cl contg), 134 (100). 6a : 1H NMR δ (CDCl3) 0.85 (t, 3H, J
) 7 Hz), 1.3-1.6 (m, 6H), 2.9 (s, 6H), 2.78 (m, 1H), 3.6 (AB
part of an ABX system, 2H), 6.75 and 7.05 (AA′BB′, 4H); 13C
NMR δ (CDCl3) 13.9 (CH3), 22.5 (CH2), 29.5 (CH2), 32.5 (CH2),
40.5 (CH3), 47.1 (CH), 50.1 (CH2), 113.5 (CH), 126.2 (CH),
133.2, 149.4; GC/MS m/z 241 (13), 239 (25, Cl contg), 190 (70),
182 (20, Cl contg), 134 (100), 120 (30).
The reaction in the presence of NaBH4 was explored
in some degree depth, since alkylanilines are of practical
significance both as strong and selective aromatase
inhibitors16 and as liquid crystals components17 but are
presently prepared through multistep procedures such
as the nitration of alkylbenzenes. The present method,
based on the slow addition of NaBH4 to the irradiated
solution to maintain a constant steady-state concentra-
tion of the reducing agent, gave encouraging results with
all of the alkenes tested. The ratio of alkylated anilines
vs reduced anilines was 1.1 to 2.1, and within the first
group the ratio of alkylanilines vs â-chloroalkylanilines
was 5 to >10. This demonstrates the possibility of
differentiating the trapping of phenyl cation 29 and of
the adducts 30-32, since control experiments showed
that the products did not arise from a subsequent
reduction of the chloroalkylanilines.
Furthermore, this procedure may have some prepara-
tive significance in view of the fact that it leads in a single
step to the desired alkylanilines and these are easily
separated from the main byproducts, nonalkylated anilines
2, and purified by bulb-to-bulb distillation.
Con clu sion
The smooth generation of triplet 4-aminophenyl cations
by photolysis of the corresponding chloroanilines in
moderately polar solvents offers the possibility of exploit-
ing the selective electrophilic reactions of such species,
in particular the propensity for attack to π, rather than
σ, nucleophiles. In this way, a ionic analogue of the
Meerwein arylation of alkenes has been found, which has
a different scope (electron-rich rather than electron-poor
olefins are attacked) and, judging from the results
presented here, a large application. The versatile pho-
tochemical generation of the intermediate phenyl cation,
requiring only that a moderately polar to polar medium
is used, allows for a considerable degree of variations.
These are based on the characteristic selectivity of triplet
phenyl cations. As demonstrated both by B3LYP analysis
and by experiments, these behave as electrophilic diradi-
cal and add efficiently to alkenes but not to neutral σ
nucleophiles, whereas the thus resulting adduct cations
react unselectively with nucleophiles. In this way, a range
of alkyl- and â-substituted alkylanilines are obtained in
a single step from chloroanilines. In view of the simplicity
of the method, these synthesis may have some prepara-
tive value. Explorative studies are under way to more
fully develop both the generation of the phenyl cation,
by extending the method to other electron-donating
substituted haloaromatics, and the exploitation of inter-
mediate alkyl cations such as 30-32, through further
selective trappings.
4-(2-Ch lor oh exyl)a n ilin e (5b) a n d 4-(1-ch lor om eth yl-
p en tyl)a n ilin e (6b) were obtained as a mixture (oil), to which
the NMR characterization is referred. Satisfactory separation
and characterization was obtained by GC/MS. Anal. Found:
C, 67.85; H, 8.40; N, 6.72. Calcd for C12H18 NCl: C, 68.07; H,
8.57; N, 6.62. 5b: 1H NMR δ (CDCl3) 0.95 (t, 3H, J ) 7 Hz),
1.2-2.0 (m, 6H), 2.96 (AB part of an ABX system, 2H), 3.7
(broad, 2H, exch), 4.1 (X part, 1H), 6.73 and 7.05 (AA′XX′, 4H);
13C NMR δ (CDCl3) 13.9 (CH3), 22.1 (CH2), 28.5 (CH2), 37.0
(CH2), 44.2 (CH2), 64.6 (CH-Cl), 115.1 (CH), 130.1 (CH), 132.0,
1
144.8; GC/MS m/z 211 (10, Cl contg), 106 (100). 6b: H NMR
δ (CDCl3) 0.9 (t, 3H, J ) 7 Hz), 1.3-2.0 (m, 6H), 2.8 (m, 1H),
3.6 (AB part of an ABX system, 2H), 3.7 (broad, 2H, exch), 6.8
and 7.01 (AA′XX′, 4H); 13C NMR δ (CDCl3) 13.9 (CH3), 22.5
(CH2), 29.4 (CH2), 32.7 (CH2), 47.3 (CH), 50.2 (CH2), 115.2
(16) Hartmann, R. W.; Batzl, C. Eur. J . Med. Chem. 1992, 27, 537.
(17) Byron, D. J .; Matharn, A. S.; Rees, M.; Wilson, R. C. Mol. Cryst.
Liq. Cryst. Sci. Technol. Sect. A 1995, 258, 229.

Photoinduced, Ionic Meerwein Arylation of Olefins
J . Org. Chem., Vol. 66, No. 19, 2001 6351
(CH), 128.5 (CH), 133.5, 144.9; GC/MS m/z 211 (18, Cl contg),
162 (60), 154 (28, Cl contg), 19 (38), 106 (100), 91 (12).
N,N-Dim eth yl-4-(1,1,2-tr im eth yl-2-pr open yl)an ilin e (8a)
was obtained as an oil. Anal. Found: C, 65.85; H, 5.10; N,
12.72. Calcd for C14H21 N: C, 82.70; H, 10.41; N, 6.89. Data:
1H NMR δ (CDCl3) 1.45 (s, 6H), 1.6 (s, 3H), 2.95 (s, 6H), 4.85
(bs, 1H), 4.97 (bs, 1H), 6.7 and 7.2 (AA′XX′, 4H); 13C NMR δ
(CDCl3) 20.0 (CH3), 28.3 (CH3), 40.5 (CH3), 42.3, 108.7 (CH2),
112.3 (CH), 126.6 (CH), 136.3, 148.5, 155.2.
at 51.1 in 20a and at 49.0 in 20a ′). With DMSO as the solvent
the OH signal was apparent in the 1H NMR spectrum (6.12
ppm), while in CDCl3 it was too broadened for a unambiguous
identification. 20a : 1H NMR δ (CDCl3) 2.0 and 2.5 (m, 2H),
2.88 (s, 6H), 3.25 (m, 1H, H-3), 4.1-4.2 (m, 2H, H-5), 5.42 (d,
J ) 2.5 Hz, 1H, H-2), 6.7 and 7.03 (AA′XX′, 4H);13C NMR δ
(CDCl3) 32.7 (CH2), 40.6 (CH3), 51.3 (CH-3), 67.4 (CH2), 104.1
(CH-2), 112.8 (CH), 127.7 (CH), 129.5, 149.4. 20a ′: 1H NMR δ
(CDCl3) 2.1 and 2.5 (m, 2H), 2.93 (s, 6H), 3.25 (m, 1H, H-3),
4.0 and 4.3 (m, 2H, H-5), 5.46 (d, J ) 4 Hz, 1H, H-2), 6.75 and
7.05 (AA′XX′, 4H);13C NMR δ (CDCl3) 28.1 (CH2), 40.6 (CH3),
49.0 (CH-3), 67.1 (CH2), 98.5 (CH-2), 112.6 (CH), 129.2 (CH),
129.5, 149.7.
N,N-Dim eth yl-4-(2-m eth oxyh exyl)a n ilin e (21a ) was ob-
tained as an oil. Anal. Found: C, 76.15; H, 10.95; N, 5.70.
Calcd for C15H25ON: C, 76.54; H, 10.71; N, 5.95. Data: 1H
NMR δ (CDCl3) 0.9 (t, 3H, J ) 7 Hz), 1.2-1.5 (m, 6H), 2.7 and
2.8 (AB part of an ABX system, 2H), 2.95 (s, 6H), 3.35 (m, 1H,
H-2), 3.38 (s, 3H, OMe), 6.7 and 7.05 (AA′X′, 4H); 13C NMR δ
(CDCl3) 13.9 (CH3), 22.7 (CH2), 27.4 (CH2), 33.0 (CH2), 38.9
(CH2), 41.0 (NCH3), 56.8 (OMe), 82.5 (CH-2), 113.1 (CH), 129.9
(CH), 133.9, 144.2; GC/MS m/z 235 (10), 134 (100). GC/MS
analysis of the raw photolyzate showed a peak at a slightly
lower tR compatible with the structure of N,N-d im eth yl-4-
(1-m eth oxym eth ylp en tyl)a n ilin e (22a ): m/z 235 (12), 203
(15), 164 (100), 149 (25).
4-(2-Meth oxyh exyl)a n ilin e (21b). Anal. Found: C, 75.15;
H, 10.40; N, 6.50. Calcd for C13H21ON: C, 75.31; H, 10.21; N,
6.76. Data: 1H NMR δ (CDCl3) 0.9 (t, 3H, J ) 7 Hz), 1.2-1.5
(m, 6H), 2.7 (AB part of an ABX system, 2H), 3.3 (m, 1H, H-2),
3.35 (s, 3H, OMe), 3.7 (broad, 2H, exch), 6.73 and 7.03 (AA′XX′,
4H); 13C NMR δ (CDCl3) 14.0 (CH3), 22.7 (CH2), 27.5 (CH2),
31.7 (CH2), 39.1 (CH2), 56.8 (OMe), 82.5 (CH-2), 115.1 (CH),
130.1 (CH), 133.9, 144.2; GC/MS m/z: 207 (25), 106 (100). GC/
MS analysis of the raw photolyzate showed a peak at a slightly
lower tR compatible with the structure of 4-(1-m et h oxy-
m eth ylp en tyl)a n ilin e (22b): m/z 207 (6), 136 (100).
P r ep a r a tive Exp er im en ts in th e P r esen ce of Sod iu m
Iod id e. A solution of N,N-dimethyl-4-chloroaniline (1a , 94 mg,
0.02 M) or of 1b (76 mg) in 30 mL of acetonitrile containing
0.015 M sodium iodide and 1 M 1-hexene was subdivided in
two quartz tubes, flushed with argon for 15 min, and irradiated
in a merry-go-round apparatus by means of 6 external 15 W
phosphor-coated lamps (center of emission 310 nm) for 25 or
50 min (this limited the conversion to ca. 60%). Work up was
as above.
4-(1,1,2-Tr im eth yl-2-p r op en yl)a n ilin e (8b) was obtained
as an oil. Anal. Found: C, 65.85; H, 5.10; N, 12.72. Calcd for
C
12H17 N: C, 82.23; H, 9.78; N, 7.99. Data: 1H NMR δ (CDCl3)
1.4 (s, 6H), 1.54 (bs, 3H), 3.0 (broad, 2H, exch), 4.85 (bs, 1H),
4.95 (bs, 1H), 6.65 and 7.1 (AA′XX′, 4H); 13C NMR δ (CDCl3)
20.0 (CH3), 28.4 (CH3), 42.9, 108.9 (CH2), 114.5 (CH), 126.8
(CH), 138.5, 143.7, 148.5, 153.1.
tr a n s-2-Ch lor o-1-(4-a m in op h en yl)cyclop en ta n e (10b)
was obtained as an oil. Anal. Found: C, 67.80; H, 7.35; N, 7.05.
Calcd for C11H14 NCl: C, 67.51; H, 7.21; N, 7.16. Data: 1H
NMR δ (CDCl3) 1.7-2.4 (m, 6H), 3.15 (m, 1H, H-1), 3.7 (broad,
2H, exch), 4.12 (m, 1H, H-2), 6.7 and 7.05 (AA′XX′, 4H). The
NOE difference spectra supported the trans spatial relation-
ship between H-2 and H-1: the irradiation of H-1 caused a
weak signal enhancement for H-2 due to coupling not to spatial
proximity. 13C NMR: δ (CDCl3) 22.4 (CH2), 32.0 (CH2), 36.1
(CH2), 54.6 (CH), 66.4 (CH), 115.2 (CH), 127.9 (CH), 132.1,
144.9. GC/MS: m/z 195 (40, Cl contg), 160 (25), 132 (100).
tr a n s-2-Ch lor o-1-(N,N-d im eth yl-4-a m in op h en yl)cyclo-
h exa n e (12a ) was obtained as an oil. Anal. Found: C, 70.90;
H, 8.55; N, 5.75. Calcd for C14H20NCl: C, 70.72; H, 8.48; N,
5.89. Data: 1H NMR δ (CDCl3) 1.4-1.6 (m, 4H), 1.7-2.0 (m,
3H), 2.4 (m, 1H), 2.62 (dt, J ) 11, 4 Hz, 1H, H-1), 2.95 (s, 6H),
4.0 (dt, J ) 11, 4 Hz, 1H, H-2), 6.75 and 7.05 (AA′XX′, 4H).
The large coupling constant between H-1 and H-2 (11 Hz)
proved their trans spatial relationship. 13C NMR: δ (CDCl3)
25.8 (CH2), 26.5 (CH2), 35.6 (CH2), 37.9 (CH2), 40.5 (CH3), 52.5
(CH), 65.1 (CH), 112.4 (CH), 127,8 (CH), 131.9, 149.3. GC/
MS: m/z 209 (60, Cl contg), 174 (10), 132 (100).
tr a n s-2-Ch lor o-1-(4-am in oph en yl)cycloh exan e (12b) was
obtained as an oil. Anal. Found: C, 68.65; H, 7.60; N, 6.55.
Calcd for C12H16NCl: C, 68.73; H, 7.69; N, 6.68. Data: 1H NMR
δ (CDCl3) 1.3-2.4 (m, 8H), 2.6 (dt, J ) 11, 4 Hz, 1H, H-1),
3.65 (broad, 2H, exch), 3.95 (dt, J ) 11, 4 Hz, 1H, H-2), 6.7
and 7.02 (AA′XX′, 4H). The large coupling constant between
H-1 and H-2 (11 Hz) proved their trans spatial relationship.
13C NMR: δ (CDCl3) 25.8 (CH2), 26.5 (CH2), 35.6 (CH2), 37.9
(CH2), 52.6 (CH), 64.9 (CH), 115.1 (CH), 128.4 (CH), 134.1,
144.8.
N,N-Dim eth yl-4-(2-iod oh exyl)a n ilin e (23a ) a n d N,N-
d im eth yl-4-(1-(iod om eth yl)p en tyl)a n ilin e (24a ) were ob-
tained as a mixture to which the NMR characterization and
elemental analysis are referred. The former was predominant.
Anal. Found: C, 50.55; H, 6.40; N, 4.10. Calcd for C14H22 NI:
C, 50.77; H, 6.69; N, 4.23. The 2D-HSQC experiment identified
the carbon to which the iodine was bonded. In detail the proton
at 4.27 ppm correlated with the carbon at 40.1 in the main
isomer while the methylene group at 3.35 ppm correlated with
the carbon at 15.9 ppm in the minor one. 23a : 1H NMR δ
(CDCl3) 0.9 (t, 3H, J ) 7 Hz), 1.3-1.6 (m, 6H), 2.9 (s, 6H),
3.25 and 3.09 (AB part of an ABX system, J gem ) 14 Hz, 2H,
CH2I), 4.27 (m, X part, 1H, H-2), 6.7 and 7.05 (AA′XX′, 4H);
13C NMR δ (CDCl3) 14.4 (CH3), 22.3 (CH2), 32.3 (CH2), 39.3
(CH2), 40.9 (CHI), 41.2 (NCH3), 47.1 (CH2), 113.1 (CH), 130.1
(CH), 134.0, 149.4; GC/MS m/z 331 (35), 204 (60), 134 (100).
5-((N,N-Dim et h yl-4-a m in op h en yl)m et h yl)-2,3,4,5-t et -
r a h yd r o-2-fu r a n on e (18a ) was obtained as an oil. Anal.
Found: C, 71.20; H, 7.75; N, 6.30. Calcd for C13H17 O2N: C,
71.21; H, 7.81; N, 6.39. Data: 1H NMR δ (CDCl3) 2.0 (m, 1H),
2.1-2.5 (m, 3H), 2.85 and 3.0 (AB part of an ABX system, 2H),
2.95 (s, 6H), 4.7 (qui, J ) 7 Hz, 1H, H-5), 6.65 and 7.05
(AA′XX′, 4H); 13C NMR δ (CDCl3) 26.8 (CH2), 28.5 (CH2), 40.1
(CH2), 40.6 (NCH3), 81.1 (CH-5), 112.8 (CH), 130.0 (CH), 134.3,
149.5, 177.1.
3-(N,N-Dim eth yl-4-a m in op h en yl)-2-h yd r oxy-2,3,4,5-tet-
r a h yd r ofu r a n (20a ) was obtained as colorless crystals, mp
98-100 °C. Anal. Found: C, 69.75; H, 8.35; N 6.40. Calcd for
C
12H17 O2N: C, 69.54; H, 8.27; N, 6.76. Data: GC/MS m/z 207
(60), 189 (30), 178 (40), 160 (100). This hemiacetal is present
in solution as a mixture of the trans (20a ) and cis (20a ′)
diastereoisomers, their proportion being solvent dependent.
The former isomer was in every case the main one, but in
CDCl3 solution the trans/cis ratio was 4:1, while in DMSO or
CD3COCD3 it became 8:1. In the proton spectrum the respec-
tive H-2 signals fell very close (5.42 and 5.46 ppm) so that a
NOE experiment to verify the relative configuration was
precluded. The two isomers were distinguished on the basis
of the carbon chemical shifts, with reference to the known fact
that, in 1,2-disubstituted cyclopentane derivatives, the cis
spatial arrangement causes shielding of the two carbon
involved compared with the trans arrangement (CH-2 ap-
peared at δ 104.1 in 20a and at δ 98.5 in 20a ′; CH-3 appeared
1
24a : H NMR δ (CDCl3) 0.88 (t, 3H, J ) 7 Hz), 1.2-1.8 (m,
6H), 2.8 (m, H-1) 2.95 (s, 6H), 3.35 (d, J ) 7 Hz, 2H, H-1), 6.7
and 7.05 (AA′XX′, 4H); 13C NMR δ (CDCl3) 14.4 (CH3), 15.9
(CH2I), 22.6 (CH2), 29.7 (CH2), 33.1 (CH2), 41.1 (CH3), 47.7
(CH), 113.1 (CH), 128.4 (CH), 133.3, 148.4; GC/MS m/z 331
(25), 204 (85), 134 (100).
4-(2-Iod oh exyl)a n ilin e (23b) a n d 4-(1-(iod om eth yl)-
p en tyl)a n ilin e (24b) were obtained as a mixture to which
the NMR characterization and elemental analysis are referred.
Satisfactory separation and characterization was obtained by
GC/MS analysis. Anal. Found: C, 47.35; H, 6.10; N, 4.55. Calcd
for C12H18 NI: C, 47.54; H, 5.98; N, 4.62. 23b: 1H NMR δ
(CDCl3) 0.9 (t, 3H, J ) 7 Hz), 1.2-1.8 (m, 6H), 3.05 and 3.2

6352 J . Org. Chem., Vol. 66, No. 19, 2001
Mella et al.
(AB part of an ABX system, J gem ) 14 Hz, 2H, CH2I), 3.6-3.7
(broad, 2H, exch), 4.2 (m, X part, 1H, H-2), 6.8 and 7.0 (AA′XX′,
4H); 13C NMR δ (CDCl3) 13.8 (CH3), 21.8 (CH2), 31.7 (CH2),
38.8 (CH2), 40.2 (CHI), 46.6 (CH2), 115.2 (CH), 129.8 (CH),
133.3, 144.6; GC/MS m/z 303 (10), 176 (30), 106 (100). 24b:
1H NMR δ (CDCl3) 0.85 (t, 3H, J ) 7 Hz), 1.2-1.8 (m, 6H),
2.75 (m, H-1), 3.3 (AB part, 2H, H-1), 3.6-3.7 (broad, 2H, exch),
6.7 and 6.95 (AA′XX′, 4H); 13C NMR δ (CDCl3) 13.8 (CH3), 15.1
(CH2I), 22.4 (CH2), 29.7 (CH2), 33.2 (CH2), 47.3 (CH), 115.1
(CH), 128.1 (CH), 133.3, 148.4; GC/MS m/z 303 (10), 176 (40),
106 (100).
P r ep a r a tive Exp er im en ts in th e P r esen ce of Sod iu m
Bor oh yd r id e. A solution of N,N-dimethyl-4-chloroaniline (1a ,
1.09 g, 0.05 M) or of 1b (0.89 g) in 140 mL of acetonitrile
containing 17.5 mL of 1-hexene (1 M), 100 mg of sodium
borohydride (0.019 M), and 200 mg of potassium carbonate
(0.01 M) was irradiated for 3 or 6 h in an immersion well
apparatus fitted with an high-pressure mercury arc (125 W,
water-cooled through a quartz jacket) after 15 min of flushing
with argon and maintaining a slow gas flux during the
irradiation. A solution of 300 mg of NaBH4 and 200 mg of K2-
CO3 in 15 mL of water was slowly added during the irradiation
period. The reaction was followed by GC, showing that the
proportion of alkylanilines 25a ,b with respect to reacted 1a
remained constant except for some decrease in favor of aniline
2a and chloroalkylanilines 5a and 6a above 70% conversion.
Work up was as above.
N,N-Dim eth yl-4-cycloh exyla n ilin e (28a ) was obtained
as an oil. Anal. Found: C, 82.35; H, 10.20; N, 6.50. Calcd for
C14H21N: C, 82.70; H, 10.41; N, 6.89. Data: 1H NMR δ (CDCl3)
1.3-2.0 (m, 10H), 2.5 (m, 1H), 2.95 (s, 6H), 6.75 and 7.03
(AA′XX′, 4H); 13C NMR δ (CDCl3) 26.1 (CH2), 26.9 (CH2), 34.6
(CH2), 40.8 (NCH3), 43.4 (CH), 112.8 (CH), 127.2 (CH), 136.5,
148.9.
Low -Con ver sion Exp er im en ts. Low conversion experi-
ments were carried out for quantum yields measurements
(Table 2) and competition experiments (Table 3). The solutions
(5 mL) were prepared and irradiated under the same condi-
tions as in the preparative experiments. Alternatively, 2 mL
portions were irradiated in spectrophotometric couvettes by
means of a 200 W focalized high-pressure mercury arc
(interference filter, λtr 313 nm). In every case the conversion
was limited to 20%. Product formation was assessed by GC
and HPLC. The light flux was measured by ferrioxalate
actinometry.
Ca lcu la tion s. The singlet (1A′) and triplet (3B2) states of
+
the H2N-C6H4 cation as well as the intermediates arising
from the addition reaction to ethylene and water were opti-
mized by the standard (U)B3LYP method by using the 6-31G-
(d) basis set, as implemented in the Gaussian 94 program.24
The singlet (1A′) and triplet (3B2) states of the cation were also
optimized at the 6-311+G(d,p) level of theory. Both states were
characterized by harmonic frequency calculations at B3LYP/
6-31G(d) level. To confirm the nature of the stationary points
and to produce theoretical parameters, vibrational frequencies
(in the harmonic approximation) were calculated by B3LYP/
6-31G(d) and used with no scaling for computing the zero point
energies and their contributions to Gibbs free energies.
N,N-Dim eth yl-4-h exylan ilin e (25a)15 an d N,N-dim eth yl-
4-(1-m eth ylp en tyl)a n ilin e (26a ) were obtained as a mixture
to which the NMR characterization and elemental analysis are
referred. Satisfactory separation and characterization were
obtained by GC/MS analysis. Anal. Found: C, 81.75; H, 11.15;
N, 6.75. Calcd for C14H23 N: C, 81.89; H, 11.29; N, 6.82. 25a :
1H NMR δ (CDCl3) 0.9 (t, 3H, J ) 7 Hz), 1.2-1.7 (m, 8H), 2.53
(t, J ) 7 Hz, 2H, H-1), 2.93 (s, 6H), 6.72 and 7.08 (AA′XX′,
4H); 13C NMR δ (CDCl3) 14.0 (CH3), 22.5 (CH2), 26.8 (CH2),
28.9 (CH2), 31.7 (CH2), 34.8 (CH2), 38.2 (CH2), 40.8 (NCH3),
112.9 (CH), 128.8 (CH), 131.2, 148.8; GC/MS m/z 205 (38), 134
(100). 26a : 1H NMR δ (CDCl3) 0.88 (t, 3H, J ) 7 Hz), 1.23 (d,
J ) 7 Hz, 3H), 1.5-1.7 (m, 6H), 2.62 (m, 2H, H-1), 2.95 (s,
6H), 6.74 and 7.08 (AA′XX′, 4H); 13C NMR δ (CDCl3) 13.9
(CH3), 22.4 (CH2), 22.7 (CH2), 29.9 (CH2), 31.7 (CH2), 38.7 (CH),
40.8 (NCH3), 112.7 (CH), 127.4 (CH), 136.2, 148.8; GC/MS m/z
205 (32), 148 (100).
Ack n ow led gm en t. Partial support of this work by
the MURST, Rome, is gratefully acknowledged. A gift
of silica gel by Millipore is gratefully acknowledged.
Su p p or tin g In for m a tion Ava ila ble: Complete compu-
tational results in the form of tables of Z-matrixes with the
computed total energies. This material is available free of
charge via the Internet at http://pubs.acs.org.
4-Hexyla n ilin e (25b)16 a n d 4-(1-m eth ylp en tyl)a n ilin e
(26b)17 were obtained as a mixture to which the NMR
characterization and elemental analysis are referred. Satisfac-
tory separation and characterization were obtained by GC/MS
analysis. Anal. Found: C, 81.15; H, 10.90; N, 7.85. Calcd for
J O010469S
(18) Iyer, R. N.; Rao, K. V. B. Indian J . Chem. B 1978, 16, 601. Eisch,
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C
12H19 N: C, 81.30; H, 10.80; N, 7.90. 25b: 1H NMR δ (CDCl3)
0.85 (t, 3H, J ) 7 Hz), 1.2-1.7 (m, 8H), 2.55 (t, J ) 7 Hz, 2H,
H-1), 3.6 (broad, 2H, exch), 6.67 and 7.1 (AA′XX′, 4H); 13C NMR
δ (CDCl3) 14.0 (CH3), 22.5 (CH2), 26.8 (CH2), 28.9 (CH2), 31.7
(CH2), 34.9 (CH2), 38.2 (CH2), 115.2 (CH), 129.0 (CH), 133.1,
143.9; GC/MS m/z 177 (20), 106 (100). 26b: 1H NMR δ (CDCl3)
0.9 (t, 3H, J ) 7 Hz), 1.23 (d, J ) 7 Hz, 3H), 1.2-1.7 (m, 6H),
2.85 (sext, J ) 7 Hz, 2H), 3.6 (broad, 2H, exch), 6.68 and 7.01
(AA′XX′, 4H); 13C NMR δ (CDCl3) 13.9 (CH3), 22.5 (CH2), 22.7
(CH2), 29.9 (CH2), 31.6 (CH2), 38.9 (CH), 115.2 (CH), 127.6
(CH), 138.2, 143.8; GC/MS m/z 177 (20), 120 (100).
(23) Galewski, Z. Mol. Cryst. Liq. Cryst. 1987, 151, 233. Datyner,
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(24) Frisch, M. J .; Trucks, G. W.; Schlegel, H. B.; Gill, P. M. W.;
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G. A.; Montgomery, J . A.; Raghavachari, K.; Al-Laham, M. A.;
Zakrzewski, V. G.; Ortiz, J . V.; Foresman, J . B.; Cioslowski, J .;
Stefanov, B. B.; Nanayakkara, A.; Challacombe, M.; Peng, C. Y.; Ayala,
P. Y.; Chen, W.; Wong, M. W.; Andres, J . L.; Replogle, E. S.; Gomperts,
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94, revision E.3; Gaussian, Inc.: Pittsburgh, PA, 1995.
4-Cyclop en tyla n ilin e (27b)10 was obtained as an oil.
Data: 1H NMR: δ (CDCl3) 1.5-2.1 (m, 8H), 2.9 (qui, J ) 8
Hz, 1H), 3.5 (broad, 2H, exch), 6.65 and 7.05 (AA′XX′, 4H);
13C NMR δ (CDCl3) 20.9 (CH2), 34.5 (CH2), 45.1 (CH), 115.0
(CH), 127.7 (CH), 136.4, 144.0; GC/MS m/z 175 (50), 132 (100),
106 (45).