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Asymmetric Reaction of Arylalkenes with Diselenides.

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[lo] a j E . J. Corey. M. Chaykovsky. J. . h i . C'hem. S W . 1965. 87. 1353: h) T G.
Waddell. P. A. Ross, J Org. Chciu. 1987, 52. 4802. We thank Dr. Craig A.
Coburn and Dr. William G. Bornmann for developing :ind optimizing these
steps.
[ l l ] a ) J . J. Masters, D. Jung. S. J. Danishefsky. L. B. Snyder. T. K. Park. R. C. A.
Isaacs. C . A. Alaimo. W. B. Young. A i i g m . Chcni 1995. 107, 495; , 4 i l p > t
C'heni. In/. Ed. Engl. 1995, 34. 452: h) For a related degradation of a C D
f'ragment see: M. J. Di Grandi. C. A. Coburn. R . C. A. Isoacs. S.J. Dnnishcfhky. J Or,?. Chwii. 1993.5H. 7728: c) J. J. Masters, D. K. .lung. W. G. Bornmann.
S. J. Danishefsky. Tciruiietiron Lcrt. 1993. 34, 7253.
(121 a ) Y Queneau. W. J. Krol. W. G . Bornni:uin, S. J. Danishefskq. J. Orx. Chcn~.
1992. J7. 4043; b) M. J. Di Grandi. D. K . Jung. W J. Krol. S. J. Danishefsky.
[hid 1993.58.4989.c) For an earlier example of this ctrategy we' A. S. Kcnde.
S. Johnson. P. Sanfilippo, J. C. Hodgec. L. N . Juiigheiin. J. A m C ' / i m i . .So(
1986, / f M , 3513
1131 a ) M. H. Kress. R. Ruel. W. H Miller. Y. Kishi. 7i.rrahc~rlroii L<,r/.1993. 34,
5999: b j ihid. 1993. 34. 6003.
[I41 Poi- a revieb on the Heck redction see' A. dc Mekjere. t. E Meycr. . A I I , ~ w .
Chiwi. 1994, fO6. 2473: .A/rgmv. C'heiw. I n / . Ed O i , y / . 1994. 33. 2379.
[Is] G. Berti. R J ~SICI.EOC/?CI?I.
.
1973. 7. 93. ;ind rcfcrenccs tlicrc~ii
[I61 Dcpi-otcction of 31 a proved to he problematic a n d revealed that protectin,.
group manipulations must be performed o n compounds conl;iining the cnrhoiiate group. The crystal structure of 31 a sccurcd :ill 01' tliv btcreochemic;il
assignment? made in the course of the synthesis before the target system w,ii?
reached
~
with selenium compounds, in particular, offer attractive possibilities. However. so far only a few asymmetric variants of these
reactions are known since the chiral precursors can only be
prepared by multistep syntheses with low overall yield^.[^.^]
In the following new and readily accessible chiral diselenides
will be described, which show interesting stereoselectivities on
addition to alkenes. After activating the diselenides by conversion into selenium cations, the alkenes are added in the presence
of a nucleophile, and subsequently the addition products can be
isolated in good yields. The selenium compounds obtained in
this way are suitable for further reaction^.'^' Since they are potential radical precursors, the whole palette of radical reactions
is available. Deprotonation of the selenides in the %-position to
the selenium and oxidative elimination offer possibilities for
further functionalizations.
The diselenides (S.S)-2 are synthesized from the chiral alcohols (S)-l,'"]
which are obtained by reduction of the ketones
with ( - )-B-chlorodiisopinocampheylborane [(Ipc),BCl] in
enantiomeric excesses of 93-96°/".[71 The krtoncs are accessible
by Grignard reaction from 2-bromobenzaldehyde and the subsequent oxidation with chromium(vr) oxide.[81After alkylation
of 1 (only if the desired product is 2, R + H ) the resulting
product is lithiated and worked up oxidatively after the addition
of elemental selenium. The chiral diselenides 2 are isolated in
overall yields of 50-60O/b.
31a
[ 1 7 ] W. B. Young, J. T. Link. J. J. Masters. L B. Snyder, S. J. Danishefsky. P/ruhedron k t t . . 1995, 36, 4963.
[IS] K. C. Nicolaou, J. Renaud, P. G . Nantermet, E. A. Couladouros. R. K . Guy.
W. Wrasidlo, J. Ain. Chem. SOC.1995. 117, 2409.
[19] For a review on the applications of samarium diiodide in organic synthesis see:
G . A. Molmder. Chmi. Rev. 1992, Y2. 29
[20] Synthetic baccatin I l l (2) was identical to a natural sample by TLC. ' H NMR.
''C
NMR, and I R spectroscopy. high-resolution mass spectrometry, and
optical rotation.
Asymmetric Reaction of Arylalkenes
with Diselenides""
Thomas Wirth*
Reactions for the functionalization of non-activated C=C
double bonds are an integral part in the repertoire of the synthetic chemist; however there are not many stereoselective variants of these reactions.", Stoichiometric addition reactions of
chiral reagents can be used advantageously for asymmetric synthesis, especially since some of these adducts can also be further
functionalized. Functionalizations of non-activated alkenes
[*I
Table I Reaction of(S.Sj-diselenides with styrene to give the addition products 3.
DiR
selenide
Za
Dr. T. Wirlh
lnstitut fur Organische Chemie der Universitlt
2a
2b
2c
St. Johanns-Ring 19, CH-4056 Basel (Switzerland)
2d
Telefax: Int. code + (61)322-6017
e-mail: wirth(o ubaclu.unibas.cl1
[**I
The diselenides 2 were initially treated with bromine to yield
the bromides. which were subsequently allow to react with silver
triflate to give the more reactive triflates. Coordination of the
oxygen of the OR group to the selenium cation leads to the
formation of a heterocycle in a fixed conformation; on addition
of the alkene the chirality is transferred to the newly formed
asymmetric centers. This is confirmed by analysis of the addition products 3. For the diselenides 2a-2d (R' = Me. Table I )
the ability of the oxygen to coordinate to selenium is influenced
by the size of the substituents R : the larger the substituent R the
weaker the coordination of oxygen to selenium and therefore
the weaker the inducing effect on the newly formed stereocenter.
Thus. compound 2a with R = H shows the highest diastereoselectivity on addition to styrene. A further indication of the
coordinative effect is revealed by the 77SeN M R shifts of the
diselenides: the signal of the diselenide 2a at (5 = 446 is shifted
This work w,:is ?upported by the Fonds der Chemischen Industrie with 11
Liehig-Stipendium. 1 would like to thank Professor B. Gie?e (or hl5 generous
support
2e
5
H
H
Me
Et
tBu
CH,CH,OMe
R'
Me
Me
Me
Me
Me
Et
7'SeNMR
T
[4
['CI
446
446
428
425
414
429
441
- 78
-100
78
78
-78
- 78
~
~
- 78
Yield
3 ["I"]
de [h]
3 [%]
70
67
63
58
77
83
74
74
68
36
54
63
60
70
[u] 6 vnlucs. [b] The w viilucs of 4 d c ~ c r m ~ n cby
d GC [7] differ only slightly (?3'/0
from the r k ~values ol' the additlon products 3
COMMUNICATIONS
by approximately 30 ppm to lower field in contrast to that of 2d
(6 = 414). The diastereomeric ratios of the addition products 3
were determined by 'H and I3C N M R spectroscopy as well as
by GC analysis1" of the cleavage products 4.[91In a separate
synthesis of (S)-4[101
it could be shown that the S-configurated
center in 2 induces an S-configuration of a new asymmetric
center in 3. thus the main diastereomer of the addition products
3 is (S.S)-configurated. The diastereoselectivity of the addition
reaction is improved if the reaction temperature of - 78 "C is
lowered to - 100 'C.
An intramolecular trapping of the selenonium compounds
formed by addition of the electrophilic selenium species is also
possible. Thus. the carboxylic acids 8 a i L 2and
] 12aiI3]react to
8b
give the lactones 9a and 13a. respectively; thc
and 12b yield the substituted tetrahydrofuran\ 9 b and 13b,
respectively. The intramolecular addition of the nucleophilc is
preferred; even on addition of six equivalents ot' methanol. the
alkenes 8 and 12 d o not form selenium-containing products with
methoxy groups. As the products I I and 13 show. quaternary
carbon centers with good asymmetric induction can be formed
by the title reaction. Alkenes without aryl groups sometimes
yield mixtures of regioisomers with lower diastcreoselectivities.
2-
21
Ph
7:
6
'
P
se),
'Table 7 . Keiiction of (S,S)-diselenides with styrene to gibe the addition products 3.
/ ' = - 100 (-.
Lhselenide
K
R'
"Se N M R
[a1
Yield
3 ["h]
dc, [b]
3 ["h]
2a
ti
H
Me
Et
riPr
446
456
456
[dl
61
53
54
33
83
2f
2g
[a] and
rBu
h
d
o
,
72% de
ArSe
XX
87
35
[bl Sec Table 1 [c] Compound 2 h was employed as a racemate (1 11. [d] Not
dcterrniiird
Other arylalkenes were also treated successfully with 2f: 2f
reacts with (E)-I -phenyl-prop-3 -ene 6 to give the addition
product 7 in 61 YOyield and 72 % de; with 2-phenyl-but-1-ene 10
the compound I I was formed in 60% yield and 82 %, de.
,,I(,
10
Ph
9a: X=O 31%. 76% de
9b: X=H2 57%, 86% de
8a: X=O
Bb: X=H,
(9-4
IJnprorected hydroxy groups (R = H) thus appear to coordinate the intermediate selenium cations well. An ethoxymethoxy
substituent in 2e which, in principle, contains two oxygen atoms
capable of coordinating to selenium causes no increase in the
diastereoselectivity in the addition reaction. The position of the
hydroxy group in the side chain in the diselenide 5 is varied, and
the coordination no longer leads to the formation of a fivemembered ring but a six-membered ring. Because of the evidently greater flexibility of the conformation, the diastereomeric
excess decreases on the addition to styrene to approximately 4 : 1
(60% d ~ ) .
In contrast. if the steric demand of R' in the diselenides 2 with
R = H is altered, a better side selectivity than in 2 a is achieved
for 2f with R' = Et and 2 g with R = nPr for the addition to
styrenc; thc diastereomeric ratio increases up to 16: 1 (88 "h de.
Table 2). For 2 h with R = fBtt this ratio decreases to about 2: 1
(35 % d e ) . This effect is presumably based on the steric strain of
the five-membered ring, which is formed by coordination of the
oxygen atom to selenium.
2 h [c]
61%.
21
5
li
Ii
-
OMe
21
__f
psb
ArSe
11: 60%.02% de
ArSep
12a: X=O
12b: X=HZ
13a: X - 0
13b: X=H2
s
x
62%. 88% de
45%. 78% de
New chiral diselenides have been presented that are readily
accessible in a few steps. In the addition to arylalkenes.
diastereoselectivities up to 88 YOwere achieved. The chiral diselenides open up new routes to asymmetric syntheses through
further functionalization of the addition products. The use of
other nucleophiles in the addition reactions its well as the synthesis of diselenides with different coordinating heteroatoms are
currently under investigation.
E.rperit?irtitnl Procidure
Synthesis 01' the diselenides 2 . I -(2-broinoph~n~l)alcolinl
I [oi- 1 -(2-hromoplienyl)
ether I,ORinsteadofOH](10 inmol)w,isplaced indry T I 1 1 ' ( 1 0 0 m L ) u n d e r a r g ~ ~ n
.it -7X C and treated sIo\\Iy with rBuLi (30 mmol). Alici- the inixtuie had been
stirred for 30 rnin at 0 C. sclenium ( I . I X g. I5 mmol. gray) x ; i ~added. l h e mixture
wa, atii-rcd fbr a n additional 3 h at 20 C. then 1 h HCI I100 mL) was added. The
resulting mixture wits extrnctcd three limes wilh rl~~-r-h~ilylinethyi
cther. and the
combined organic phases %'ere dried m i t h MgSO,. Aftci- subsequent addition of
KOH (100 rng), the solvent mas removed under viictiuiii Purification by column
chrom;itoprapIiy on silicn (pentme: rr,rr-butylmethyl ethcr 2 . I ) afforded the dise-
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
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