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New Fluorescent Model Compounds for the Study of Photoinduced Electron Transfer The Influence of a Molecular Electric Field in the Excited State.

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New Fluorescent Model Compounds for the
Study of Photoinduced Electron Transfer:
.~=~.S,~.SHZ,~H).~.~S(~.J=~.~H~.~H).~.~S
( ~ .Influence
J = ~ S H ~ .of
~ Ha) :
~ ~ C N M R Electric Field
Molecular
The
(75 MH7. CDCI,): 6 =10.3, 31.3. 74.7. 126.4, 128.3. 129.1. 130.0. 135.3. 146.5: "Se
in the Excited State**
N M R (76 MHz, CDCI,): d = 456.1:
= + 262.0 ( c = I , CHCI,,): correct ele-
lenides 2 in 50-XOViO yields a s yellow oils. Selected spectroscopic data for 2 f :
' H N M R ( 3 0 0 M H z . C D C I J : i i = 0 . 8 2 ( t . J = 7 . 0 H z . b H j . 1 65(dq.J=7.0,7.0 Hz,
4Hj. 2.2X Is, 2H). 4.76 ( t . J =7.0Hz. 2 H ) . 7.19 (dd. J = 7 5 , 7.5 Hz, 2H). 7.33 (dd.
[1]:"
mental analysis foi- C,,H,,0,Se2.
Addition ofthe diselenides 2 to atyrene: 2 (0.1 nimol) was placed in dry diethyl ether
(4 inL) under argon 'it - 78°C and bromine (0.1 1 minol. 0.1 1 mL of a 1 M solutioii
in CCI,) wis added. After 10 min silver triflate (72 mg. 0.28 minol) in methanol
(0.1 m L ) was added atid the mixture was stirred for 20 min at - 78 C. The reaction
solution s a s cooled to - 100 C and treated with styrene (0.4 mmol, 0.046 mL).
(0.3 mniol, 0.04 inL) was
After the mixture had been stirred Tor 2 h. .~~r~i.-colIidine
added. ;ind the resultant mixture was heated to 20 C and washed with 7 % aqueous
citric acid solution ( 5 mL). The organic phase was dried with MgSO,. and after
remowl of the solwnt under vacuum. thc addition product 3 was purilied by
column chroinatosraphy on silica (pentnne: rrrr-butylmethyl ether 3 : I ) . Selected
apectroscopic data for 3f. ' H N M R (300 MHz. CDCI,): 6 = 0.98 (t. J =7.4 HL.
3 H ) . 1.79 (quin,J =7.4H7. 2H). 2.41 (s. IH). 3.10-3 30(m. 2H). 3.24(s. 3Hj.4.36
(dd. J = 8 5. 5 HL. I H ) , 5.04 (in. 1Hj. 7.13- 7.51 (m. 9H); "C N M R (75 MHz.
CDCI,): 0 =10.4. 31.2.36.2. 57.0.74.7. 83.0. I26 4, 126.7, 127.6. 128.0. 118.2. 12X.6,
139.7. 133.7, 140 8. 140 0: correct elemental analysis Ibr C',,H,,O,Se.
A. Prasanna de Silva,* H. Q . Nimal Gunaratne,
Jean-Louis Habib-Jiwan, Colin P. McCoy,
Terence E. Rice, and Jean-Philippe Soumillion
~
Received: March 30. 1995
Revised veraion' April 2X. 1995 [Z7X4XIE]
German version: .4n,.q2l1 C/iiw?. 1995. 107. 1872- 1873
The elucidation of the structure and some functions of the
bacterial photosynthetic reaction center (PRC)''] has inspired
chemists to develop synthetic supramolecular systems"] and
models[31to mimic and understand some of these natural features. One of the most intriguing features of the photosynthetic
reaction center is that photoinduced electron transfer (PET)
occurs preferentially along one of two nearly identical paths.
Here we describe two simple systems, 1 and 2, which display
remarkably different PET behavior because of the presence of
different PET paths. We infer that PET in 1 and 2 is directed by
the electrical properties of the excited state itself: in other words,
PET is self-reg~lated.[~]
Keywords: asymmetric syntheses chiral diselenides . selenium
compounds
[I] H. C. Kolb. M. S. VanNieuwenhze. K . 6. Sharpless, Chrrii. R r i . 1994. Y4.
2483-2547.
121 a ) E. N. .lacobsen in C'iito/jr;c A ~ s ~ n i n i e r rSwir/ia.s;.s
i~
(Ed.: I. Ojiina). VCH,
Weinheim. 1993, pp. 1.59-202: bj B. D . Brandes. E. N Jacobsen. J Or,y Clirr71
1994. 39. 4378- 4380.
[3] a ) S. Tomoda. K.Fujita, M. Iwioka. J C k ~ w i S ~ J C
C/wn?.Conrrirurr. 1990,
129- 1 3 1 : h) K. Fiijita. M . Iwiioka. S. Tomoda. Chrrrr. Lrvr. 1994. 923 -926.
(41 R. Deziel. S. Gotilet. L. Grenier, J. Bordeleau. J. Bernier. J. Orx. C/icm. 1993.
58, 3619 3621
(51 c'. Paulinier, S r ~ k r i i i i r nReiijienrs mid 1nrcrinriliiite.c irr Or,yut?icSwir/ip.si.s,Pergamon. Oxford, 1986.
[6] M . Srcbnik. P. V Riiinachandran. H . C. Brown. J. O q . Clien7. 1988,53.1916
2920.
[7] Determination by GC. chiral column' Chrompack. /!-CD permethylated, 25 m.
[XI F. Bickelhaupt. C. Jongsma, P. de Koe. R. Lourens. N . R. Mast, G . 1.van
Mourik. H. Vermeer. R. J. M . Weustink, 7 ? . r r n h e ( h r r 1976, 32. 1921 1930.
[9] An enrichment of ii diaslereoiner in the Morkup by column chromatography
was ruled out since the NMR spectra of the crude products shoM identical
diastereomeric ratios.
[lo] H . C. BroMn, J. Chandrasckharan. P. V Rnmachandran. J. h i . C/rwi. So(
1988. 110. 1539 -1546.
[ I l l In the synthesis of the discleiiide 2h. the ketone could not be reduced with
(-)-(lpc),BCI. Compound 2h was thus employed as ii raceinate; the addilional
deterinindlion of thc diastereoselectivity by the c(' values of the ether 4 way not
carried out.
[I21 T. R. Hoye. W. S. Richardson. J. or^?. Clzm. 1989. S4. 688-693.
[I31 S. Handa. K.Jones. C. G . Nehton, Trrruhedron Lerr. 1988. 29. 3841-3844.
1141 Synthesis of the alcohols by reduction of the carboxylic acids with LiAIH,.
1a-c
2a-c
We and others have shown how PET can be exploited for the
design of fluorescent sensors for many analytes according to the
fluorophore-spacer-receptor format.[51While some of the factors that control PET have been uncovered in recent years,[61the
influence of regiochemistry is unknown. Regioisomers 1 and 2")
were designed as fluorescent PET p H sensors[81with very different electron transfer paths; all other factors were kept as constant as possible. We report here that the influence of regiochemistry on PET is very large.
The fluorescence of compound 1 a is strongly enhanced upon
protonation (Fig. I ) , as required of a fluorescent PET pH sensor
based on an aliphatic amine receptor.[51 PET occurs from the
unprotonated aminelyl to the fluorophore and causes fluorescence quenching. The PET process stops when the amine is
protonated. resulting in recovery of fluorescence. In complete
contrast, regioisomer 2a, in which the spacer-receptor unit is
linked to the fluorophore through the imide, shows only a small
reduction in fluorescence upon protonation (Fig. 1 ) . Thiscan be
attributed to fluorescence quenching in the protonated, in[*] Dr. A. P. de Silva. Dr. H. Q. N . Gunaratne, Dr. C. P. McCoy. T. E. Rice
School of Chemistry, Queen's Univeraity
Belfast BT9 SAG (Northern Ireland)
Telefax: Int. code + (1232)382117
Dr. J.-L. Hahib-Jiwan, Prof. J.-P. Soumillion
Labordloire de Chimie Organlque Physique et de Photochimie
Universite Catholique de Louvain
B-1348 Louviiin-lii-Neuve (Belgium)
Telefax: Int. code + (10)472989
[**I
This work was supported by the following organizations: NATO (grant no.
92140Xj, SERC;EPSRC (UKj. FNRS (Belgium), Department of Education in
Northern Ireland. and The Nuffeld Foundation (UK). We thank Dr. P. L. M.
Lynch for support and help.
(J570-0833/95:I6161728 $ 10.00+ .25:0
Angrw. C'hem. Irzr. Ed. EnRI. 1995, 34, N o . 16
la
Q
0 4
2a
Q
A
AAAA
A AAAAAA.
Q
A
Q Q
tramolecularly hydrogen-bonded structure 3.['01 The fluorescence of the fluorophore unit is intrinsically pH-independent, as
evidenced by the behavior of 4 (Fig. 1). Other parameters that
reflect the contrasting regiochemistry of compouiids 1 and 2 are
listed in Table 1 .
The remarkably different fluorescence beha\ iur can be easily
rationalized according to Figure 2. The 4-aminonaphthalimide
fluorophore in compounds 1 and 2 is a "push- pull" E electron
system with the 4-amino group a s donor and the naphthalimide
as acceptor. This leads to strong internal charge transfer (ICT)
in the lowest excited singlet state and considerable dipole character (positive pole at the 4-amino terminus) .I' ' ] The dipole
moment of the excited state of the model fluorophore 4 is 1 1 D
according to our measurements of solvent effects on its fluorescence and absorption spectra.[121A large dipole inoinent in an
excited state gives rise to a strong photogenerated electric field.
Such a molecular electric field can. depending on its sign and
magnitude. inhibit o r accelerate a transiting electron in 2 or 1,
respectively.['" 14] Thus the fluorescence quenching PET process is observed only if the electron leaving the unprotonated
amine donor can enter the space of the 4-aminonaphthaliniide
fluorophore across the 4-position in 1 with its attractive electric
field (Fig. 2). The corresponding PET path in 2 i b just a s feasible
thermodynamically but requires the electron to enter the Iluorophore across the imide moiety with its repulsive electric field and
is not observed. We note that the PET process. which proceeds
in opposite directions in 1 and 2 with respect to the orientation
of the fluorophore, is strongly controlled by the excited state
itself without the intervention of any outside agent. This selfregulation of PET is unprecedented and an important addition
''2% nBui3
NHnBu
NHnBu
/ \
/ \
0
-
-
3
4
Table I . P:iramcters of the ahsorption and fluorescence spectra of 1 a c. Za-c. and 4 [a]
Parainetcr
%,,,(hasc) [mi]
Is/:(hasel
~ b m l
PK,<lhl
i ,Jiicid) [nm] [cl
[D,(acid)[d]
;.,,,,,(haw)[nni] [cI
(ha\eJ[d]
F€ [el
PK:,[I1
(;icid)[ns][z]
k , ( 1 0 ~ s l][h]
k,, , [ l O " s ~ ' ] [ h ]
a"[lo" s '1 [Ill
k,,,,[lO"s- '][hl
0,(cyclohexanei[d]
@,(ethanol)[d]
T , (cydohex;inc)[ns]
rl icthiinol)[ns]
T,
~
la
2a
4
lb
Zb
lc
2c
431
4.22
449
4.22
440
8.4
538
0.76
549
0.030
25
8.7
7.1
0. 11
3.3
0.034 [n]
455
4.13
455
4.11
454
4.19
454
4.18
432
4.15
447
4.18
439
7.8
538
0.70
548
0.050
14
82
70
0.10
1.7
0.043 [n]
455
4.20
455
4.20
43 1
4.18
447
4.19
4.11
456
4.07
455
4.07
6.1
[I1
558
0 14
556
0.17
0.8
6.3
3.1
0.044
[I.m]
0.21
0.06
4 1
0.95
0.020
7.4
0.2
+I
-lJl
559
0.12
557
0.15
0.8
8.6
3.0
0.040
-[I,m]
0.23
0 07
0.41
0.50
6.0[0]
4.7
-111
-[jl
555
0.23
555
0.23
1 .0
[kl
4.2
0.055
[I1
0.18
-
-
-PI
-
111
4 1
-111
558
0.12
557
0.16
0.8
8.3
3.3
0.036
+,m]
0.19
0.07
53x
0.73
551
0.070
11
6.0
6.9
0.1 1
1 .3
0.039 [ill
-"I
111
0.94
0.83
7.6
8.3
[a) All the compounds (I a-c. Z a - c, and 4)were characterized by the full set of molecular spectroscopic techniques. 4 is a known compound and h a been photophysically
charactetved [?,I]. Electronic spectra (absorption and emission) were measured with 1 0 . ' ~ solutions in aerated methano1:water ( I :4. v:v). except i n the studies of solvent
cffecls. the samc conditions were also used for phase modulation fluorometry. The possihihty of naphthalimide ring hydrolysis was considered. hut Lliiz did not occur under
[h] These ~ a l u e weie
s
obtained
our conditions ( p H range 4 12). pH-Dependent fluorescence measurements were carried out with excitation at isosbestic wavelengths i,,,,,.
by an;ily/ing t h e pH dependence of the absorbance A at appropriate wavelengths with the equation l g [ ( A , , , ~ A ) , I ( A - A , , , ) ] = T pH f pK, [18]. Either sct of signs on the
i-ighl hand sidc of this equation can he valid. depending on the analytical wavelength chosen. lsosbestic points A,,,,, were observed for I a-c. [c] Obtained from tluoi-eacence
= 0 65 in EtOH
spectr'i which Mere corrected for wavelength dependence of response of the photon detection system by using quinine bisulfate [19]. [d] Rhodaminc H (0,
[ZOl) h i 1 3 employed as a secondary standard. Comparison of corrected spectra was necessary since the spectrum of the sccondary standard has a different shapc than those
o f 1 a c , 2 a -c. and 4.[el Factor for fluorescence enhancement induced by protons: FE = @,(acid)i@,(bdse). [f] These values are obtained by analyzing the pH dependence
@ ~ - ~ [Sa].
~ , , [g]
, " The
) l tt values I n basic solution (pH 12) are 0.1 ,in
of lluorescencc quantum yield
with the equation l g [ ( ~ , , ~ , ~ ~ ~ ~ ~ ) ~=(pH-pK:
4. rc\pectivcly. [h] Obtained from the following relations (J. B. Birks. Phomop/ij.sirs of Aroniulir. ,lilo/c~culi~s.
Wiley, New, York, 1970) in acidic and ha
@, = h , , ( k ,
h,J and T , = ( k , k n ) - ' ; for 1 a-c with the extra PET deactivation channel.
klXrT)-':lor Z a - c with the extra
= kJki
k,
kpFT)
and = ( k , I,,
intern4 hydrogcn bonding (1HB) deactivation channel,
= k,l(k, + k, + k,,,,) and T , = ( k ,
k , k , H J ' . k , is the fluorescence rate constant: k,, I\ the ratc constant for
all the other deexcitations except PET and IHB. PET processes occur only in basic solution and IHB processes only in acidic. [i] No clear isosbcstic poinc due to the negliglhle
spectral shift upon protonation. [j] Cannot be determined by this method due to the small spectral shift upon protonation. [k] Cannnot be determined with this method.
[I] Thcre IS no cvidcnce for the presence of this term. and it was therefore ignored during the kinetic analysis. [in] An upper limit can he calculated ;I\ the difference of the
h,, \:iIue\ o f 2 and 4. e g. 0.05 x 10'sCI for 2a. Even this estimate is too high. since this can include contributions from other deexcitation procesw such a s those arising
f o r model 4) IS assumed.
from m l w i t i o n and,'or aggregation. [n] These values refer to acidic solution. In basic solution. a value of 0.18 x 10's-' (the corresponding R , VBILIC
[o] There I S a n additional shorter-lived component (1 .0 ns) in this instance.
~
+
+
+ +
+ +
+ +
FLUOROPHORE
EXCITED STATE
RECEPTOR
0
FLUOR WHORE
EXCITEDSTATE
Fig. 2. Schematic representation of electron transrer to an ICT excited state of a
t,uorophorc from c in ~ n ~ r a i n o ~ e cbut
u l a ..external.3
r
Is
a
proton receptor) i n two i-egioisomei-c.Structures of the excitcd stdtes I " and 2* are
i i l w r h o u n alongsidc. The scheme doer not distinguish bctheen through-space o r
through-bond clccti-on transfer.
to the growing number of molecular processes regulated by
self-organization." '1
Large solvent effects on fluorescence quantum yields (Qr)and
lifetimes ( T ~ (obtained
)
from phase modulation fluorometry["])
are found for 1 a (Table 1 ) because its PET process is accelerated
in polar solvents.["] The corresponding effects are very small
for the regioisomer 2a, since PET processes are suppressed as
discussed above. Model fluorophore 4, which lacks an external
aliphatic amine as electron donor. does not undergo PET processes, and solvent effects are minor.
Table I also gives detailed rate constants which are calculated
from QF and zF data as described in the footnotcs. We estimate
the PET rate in 2 to be less than 0.05 x 10" s - I . which is the
difference in the k, values (see in footnote h ofTable 1 ) of 2 and
the model fluorophore 4, which lacks an "external" aliphatic
ainino group. Since k,,-, values ranging from 1.3 x 10" s - to
3.3 x 10" s - ' are found for 1 a-c, we can deduce that the selfregulation of electron transfer by the ICT excited state of the
4-aininonaplithalimide fluorophore allows the discrimination
between the two directions by a factor of at least 26-66.
In conclusion. the examination of the effects of pH and solvent on absorption and fluorescence behavior of 1 and 2 shows
that the excited state dipole of the 4-aminonaphthalimide
fluorophore can lower the kinetic barrier to electron transfer in
1 but not in 2, since the two compounds have opposite configurations in terms of the placement of the "external" aliphatic
ainino group with respect to the fluorophore.
Received: March 3. 1Y95 [Z77581E]
German vcrsion: Anjicii undtr C/iiwie 1995, 107. 18x9 1891
[ l ] a ) J. Deisenhofer, H. Michel. 4n.q.eii.. C'hni. 1989. 101. X72. Atigi'ii,. ( % e r r r . In/.
Ed. B7fil. 1989. 2N. X29: h) R. Huher. i/i;d. 1989. 101. 84Y and 1989. 28, 848:c )
7%ij P h o / o . s ~ i i / / i e / rRcuc/ion
i,
C'i,n/i,r, L'o/. 1. I / (Eds.: J. Deisenhofer. J. R. Norri$), Ac;idemic. San Dicgo. CA. U S A . 1993.
[2] Sensitized electron transfer: J.-P. Sauvage, .I -P. Collin. J.-C. Chambron. S
Guillerrez. C'. Coudret. V. Balzani. F. Barigelletti. L. de Cola. L. Flamigni.
C/ieni. Rcv. 1994. Y4.9Y3: D. Gust, T. A. Moore. A. L. Moore.Acc. CIirm. Rrs.
1993, 26. lYX, M . R . Wasielcwski, C/wnt. Rev. 1992. 92. 435, Energy transfer
from antenna groups: L. Jullien, J. Canceill. B. Valeur. E. Bnrdez. J.-M. Lehn.
. A n g i w . Chon 1994. 106, 2582: Angrit. Chon. lni. G I . Engl. 1994, 33. 2438;
Modulation of quinone redox properties: P. A . Brooksby. C . A. Hiinter. A. J.
McQuillan. D. H . Piirvis. A. E. Rowan. R. J. Shannon. R. Walsh, Angw.
Ciioii. 1994. 106. 2584: 4 n p w . C/ww Inr. E d Ltigl. 1994, 33. 2489.
[3] W. Rettig. Lyi. C'iirr. <'/icwi. 1994, 169. 253.
[4] With sensors 1 and 2 we were interested in demonstrating some degree of
analogy with the PRC from ;I functional. rather than structural. viewpoint. We
used two regioisomeric seiisors. each of which has only one PET pathway, such
that the arguments for self-regulation coiild be developcd with maximum clarity. T\io PET pathways iirc possible for one sensor molecule when two distinguishable dialkylaininoetliyl groups are attached to the iinide nitrogen and the
4-amino group of the 1.X-naphthalimide nucleus. Then the analogy with the
PRC becomes apparent cven i n structurlil terms. While sensors I and 2 do not
display 5ymmetry breaking during PET. we note that symmetry breaking within the PRC :issumcs (hiit the effects o f the protein matrix and the carotenoid
can be neglected. See refs. [lc.3]. We thank the referees for initiating these
comments.
[5] a ) R. A. Bissell. A. P. de Silva. H. Q. N. Gunaratne. P. L. M. Lynch. G. E. M.
Maguire. K R. A. S. Sandanayake. Chrm. So<,.Riv. 1992. 21, 187. b) R. A.
Bissell. A. P. de Silva. H. Q . N . Gunaratne. P. L. M . Lynch. G. E. M. Maguire.
C'. P. McCoy. K . R. A. S. Sandanayake. nqi. C'nrr. C/iem. 1993. 168. 223. c)
A. W. Czarnik. A u C/icni. Rrs. 1994. -17. 302.
[h] Influence of thermodynamic driving force: R. A. Mkircus, Angeit . C / i c n i . 1993,
105. 1161: .4ngiw. Clirni I n / .Ed. Enfil. 1993.32. 11 1: Influence of distance and
stcreochemistry: G. L. Closs. J R. Miller. Science 1988, 240, 440; M. M. Paddon-Row. A ( , < . Uwn?. Rrs. 1994. -17. 18; Intlucnce of conformation: E D.
Lewis. E. L. Burch. J A m . CIimi. So(. 1994. 116. 1159.
[7] The sensors were prepared in two stages. The derivatizition of4-chloronaphthalic anhydride wjith a n amine to yield the correspondins 4-chloronaphthaliinide is much faster than the subsequent nucleophilic aromatic substitution of
the 4-chloro group by ;in amino moiety. Proper choice of N.N-dialkyl-N-(2aminoethy1)amine or l-but)lamine as the reactant in the second step allows the
synthesis or I and 2. Synthetic procedures were adapted from a) M . S. Alexiou,
V. Tychopoulos. S. Ghorhanian. J. H . P. Tyman. R. G. Brown. P. I. Brittain. J
Cliem Soi.. Pwktn k i n . s . 7 1990. 837: b) Q . Xuhong. Z. Zhenghua. C.
Kongcliang. I 1 i . i ~Pigin. 1989. I ! . 13
[XI Protons wcrc studied in the first instance. Other guests can he studied by
changing the receptor cince t h e lluoresccnt PET sensor principle is quite gener31 151.
..
[Y] For the unprotonated forms of both l a and Z a the PET process from the
aliphatic amine to the 4-aminonaphthalimide fluorophore across the
diinethylene spacer has nexr-zero AGFF, according to the equation
+ AG,,, p " , ~[5a.b]. The oxidation potential
AG,,, = E,,, of the fluorophore is 1.09 and that of the receptor 1.19 or 1.00 V (versus
SC'E. ;icetoniti-ile solvent: hith 4 and triethylamine as models). The data for
triethylaininc are from H . Siegerman in P~.hriiyirc~.s
o/ E l e ~ r r o o , ; ~ u n i i ~ . ~ ~ n r h e . ~ i . ~ .
Pur/ I / (Ed: N. L. Weinhcrg). Wiley, New York. 1975. p. 667. C. K . Mann.
K . K . Barnes, W i w r o i /i[vnicu/ R i w i i o n s i n N o r ~ u r ~ i ~ i ~Snoi rl sw i t . Dekker. New
York. 1970. The attractive cnergy AG,,,,, ~ between
~ , , the radical ion pair (which
i s thi' product of the PET proccss) is assumed t o he -0.1 V (Z. R. Grabowski,
J. Dobkowski. P u w .App/ Chni. 1983, 55. 245).
[lo] A. Pardo. E. Martin. J. M. L. Poyato, .I J Camacho. M. F. Brana, J. M. Castellano, J Plioroclinir. P/iorohiol. A C%cm. 1987. 41. 69. propose 3 as an explanation of the shift in lluorescence wavelength but not with regard to quenching.
The presence of hydrogen bond donors near the negative pole of ICT excited
states is known to result i n tluorcscence quenching (M. D. P. de Costa, A. P. de
Silvii. S. T Piithiraiio. Cun J. Chctn. 1987. 6Y. 1416). A recent report o n a
system closely related to 2 shows pH-independent tluorescence (D. Yuan. R. G.
Brown, J Cl70n. R i x ( M ) 1994. 2346).
1111 For ii theorcgiwl study, see A . Pardo. J. Campanario. J. M . L. Poyato. J. J.
Camacho. D. Reyman. E Martin. J. Mol. Strircr. (Theocheni ) 1988. I66. 463.
[12] Our measurements of solvent effects on fluorescence and absorption spectra of
4 can be a n a l y e d with the equations l:j.Jb\
= [-2jto(ji, - ~ ~ ~ ) ~ / i c u " ] ( [ ( ~ - l ) :
(21: + I)]-[(n-l):(?n'
+I)]; + const. and
I,&,,, = [ - 2 / 1 , ( ~ 1 1 - ~ i g ) i h l . ~ ' ]
{[(i:-l):(%:
+ I ) ] - [ ( n 2 - 1):(2n2 + l ) ] ] + const.'(J. B. Birks, P/ioinph;.sirsof'
4roniu/ir Moliwirli~.~.
Wiley, New York. 1970). In these equations $1" and 11, are
thc dipole moments orthe ground and excited states. respectively. c the solvent
dielectric constant. II the refractive index. h Planck's constant. c the velocitv of
light, and u the Oiisager cavity radius (taken to be 3.3 A for 4). Ref. [7a] and
A Pardo. J. M. L. Poyato. E. Martin. J. J. Camacho, D. Reyman, 1. M. Castellano. J. Plioto(hmn. Pkoiohiol. A 1989, 46. 323 report on solvatochromism and
corrcsponding fluorescence effects of 4 and relatcd compounds but do not
determine dipole moments.
1131 For other effects caused by mo1ecul;ir electric fields due to ICT excited states.
see J. F. Ireland. P. A. H. Wyatt, Ads. Phr.s. Or,.. Chem. 1976. I?. 131: M. M.
Martin. P. Plam, N . DaiHung. Y. H. Meyer. J Bourson, B. Valeur. C%iwi.
COMMUNICATIONS
[I41
[ I S]
1161
1171
/'hi 5 / < v i . 1993. 202. 475: J. F. Letxrd. R. Lapouy;idc. U: Rettig. Piirr AppI.
(7im 1993. 03. 1705: E. M . Kosouer. D. Huppert. Aiiiiu. Rev. P/ij..\. C l i c i i i .
1986. .17. 117: H. Sliirukii. .41<, C / i < m . Re\. 1985. I S . 141: A . P . deSilca,
I<.0 . N Giiii,iratnc. P. L. M. Lynch. A .I.
Patty. G L. Spence. J C ' h n i i . So(..
/ ' i , r L i i i l r < i i i \ . 2 1993. 1611.
Wlicii i l i c tlir.riiiod!iiainic driving lbrcr Ibr P E T is cnlculated hy the usual
\Vcllcr-tk pc thci-mod) namic c cle with redox potentials. ion pairing riierpy.
mid \inglet ciicrgq ['?I.
t h w e i no opportunily to ;illow for the effect of the
photogciicr.itcd internal electric field. This appears to be due to the fact that the
Intel-niil field I S o n l y generated after photon absorption Thus the effect of the
inicriiril ficld u i i he biewed SI: bring largely kinetic. We iire grateful to a referee
l o r c.it.iIq/iii:
thi\ discussion.
Sce. foi cnaiiiplc 1) Amnhilino. J F. Sti!ddart. ,V1w .5"xvifi.\1 1994. I41 (19131
IS. P Biistci- 1.-M Lchn. A . DeCian. J. Fischer. A i i C/iciii.
~
~ 1993. 1fL7. 92:
. ! i i ? c ~ . ( iiciii /ill.E d GI,?/.1993. 33. 69: C. 0. Dierricli-Bucliecker. J. t:.
N i c r e i i K x l c i i . L P .Sauv'ige, 7 i ~ / r a / i e r l r o i iLcri. 1992, 33. 3625.
I (ir;ition. I) M . Jiimesoii. R. D Hall. A i i i i u Rci.. Biop/il,.s Biiie~rq.1984. 13.
105.
R \. fhwll. .\. P.cle Silva. W T. M . I.. Fernando. S T. Patti\~athncitliana.
I: I.: 5. D S,iinai-asinphe. / + / i i i / i i ~ / r i i i iLc/r. 1991. 32. 425.
[ 1 K] I.;
C " ) n n ~ l l \ l ~ i l ~ r "ho li i s~ i a~ i r r \
7'1iC.
, M l ~ l i \ i l r r ~ i l i e iof.\t,l/<,<
ii
l I / U i . colil/l/l~.\S/ii-
best results were obtained with trimethylsilyl tri Iluoromethanesulfonate (TMSOTf) as promoter.[51
Here we describe the synthesis of enantiomerically pure trrrrw
1.2-disubstituted cyclopentanes and cyclohexanes with three
stereogenic centers on using the chiral malonic acid derivatives
5 b-d, which were transformed by Knoevenagel condensation
with aldehydes 6 and 7 into the alkylidene-I ,3-dicarbonyl compounds 8 b - d and 9 d required for the cyclization. The chiral
malonic acid derivatives 5 b-d were synthesized by acylatioii of
the oxazolidinones 4b-dIb1 with malonic acid methyl ester chloride ( 3 ) in the presence of 4-dimethylaminopqridine (DMAP)
and triethylamine in 60-64 'YO yield. The achird oxazolidinone
4 a was also converted into 5 a in ~ O ' Y Oyield. With the acid
chloride 3 the conventional procedure of acyhtloii with deprotonated oxaz~lidinones['~
did not lead to the products 5, probably because in this case the primary step is ii deprotonation of
the malonyl chloride 3.
h i i / / i , Wilt\, Y e w J.oi-k, 1987.
[lL)] I< h V c I i ~ p ~ ) l d K
i . . L). Mielcii/, !VBS s j ? ~ Pfrhl.
.
1980. 260-264.
[?I)]I. I o p c / - A ~h c h . K K Roliatpi-~~iikerlce.
C h i i i P/ii:v. L i ~ i r1986,
.
13K. 174
0
Me0
0
-lU9-"
3
Intramolecular Allylsilane Addition
to Chiral Alkylidene-l,3-dicarbonyl Compounds
for the Synthesis of Enantiomerically Pure
trans- 1,2-Disubstituted Cyclopentanes
and Cyclohexanes""
Lut7 F Tietze" and Christian Schiinke
Did/(rrri,rl
l o Profe\.sor
CH,Cl2/OoC-> R T -
d
4
Me0
u
5
R
piperidine, HOAc
5
+
molecular sieve
M e , S i 4
CH,CI,, O°C
6 :n=l
8 .n=1
7 :n=2
9 :n=2
Hevhcrt W Rorskr
~ I wo( ( ( / \ / o i l of hw 60th hlrthday
011
The cycli/ation of compounds containing an allylsilane and a
carbonyl group provides a siinple and elegant synthesis of fiveand six-membered ring compounds."] In an analogous way.
a./i-LinsLit urated ketones and aldehydes can also be converted in
a type o f intramolecular Sakurai reaction.['] The simple and
induced diastereoselectivities of these transfoi-mations are, however. often unsatisfactory.[31 For instance, in particular the
stereoselective construction of enantiornerically pure 1,2-1rm.sdisubstituted cyclopentanes has not yet been achieved successfully with this method. Such compounds are. however, of great
interest for natural product synthesis.'']
Recently we showed that racemic 1.2-tvuns-disubstituted cyclopentancs w d cyclohexanes can be obtained in very good
simple diastereoselectivity through intramolecular allylsilane
addition from alkylidene malonates (for example. 2 from I ) ; the
Me0,C
CH,CI,,
Lewis acid
-7a0c
C0,Me
-4
1
2
TMSOTf : trans : cis = 99.6 : 0.4 ; 97 % yield
~
~~
[*I Pi-nl I>I-. L.
F Tielze. Dipl.-Chem. C Schiinke
Orpaiii\chr Chcmir der Unicersiilit
I ;iiiiiii;iiiii\ti-'i\se 2. D-.37077 Gixtingcn (Germany)
Iclci:i\: 1111. code
(.551)39-9376
Iii\11tiit Iiii
-
[**I
"6'
NEI, / DMAP
+
7 h i \ H o r h ~ i i \upported
\
by the Deutschc Forschuiigsgemeinschaft and the
b m d \ dcr ('lieiiiischen Industi-ie.
8 n=1
10
n=l
9 n=2
11
n=2
4,5,8-11
a,R=H, b,R=iPr,c.R=tBu,d,R=Bn
The Knoevenagel condensation of 5 a - d with the aldehyde 6,
which is easily accessible from 2-trimethylsilylmethylcyclohexanone by a photochemical Norrish type I cleavage,[81gave, in
the presence of piperidine and acetic acid virtually exclusively
the ( E ) isomers 8 a - d ( E : Z > 9 5 : 5 )in yields of 54-75%. The
configuration of the newly formed double bond in 8 a - d was
determined by NOESY measurements on 8 d a s well as by comparison with 14, which was obtained as
the major product ( E : Z > 9 5 : 5 )on conM e O V L O
densation of 5 d and benzaldehyde and
characterized by X-ray crystal structure
Ph I
analysis."]
'Ph
For the conversion of 8 a - d the Lewis
acids Me,AICI, EtAICI,. ZrCI,, AICI,,
14
TiCI,, and SnCI,, as well as TMSOTf
(1 .0 equiv in each case) were used as promoters. During the
cyclization of 8 a - d three new stereogenic centers apart from
those in the auxiliary were constructed. Eight enantiomerically
pure diastereoiners can therefore be formed. On conversion of
the achiral compound 8 a . four diastereomers are expected as
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