Investigations of the asymmetric intramolecular [2 + 2] photocycloaddition and its application as a simple access to novel C2-symmetric chelating bisphosphanes bearing a cyclobutane backbone

Article abstract of DOI:10.1021/jo960556y

The asymmetric intramolecular [2 + 2] photocycloaddition of αβ-enoates was evaluated as a simple access to the novel C₂-symmetric bisphosphanes 22 and 27 possessing a cyclobutane backbone. A source of different chiral auxiliaries for investigations of the photochemical key step was provided by the transacetalization of dialkyl tartrates 3 with the corresponding 3,3-dialkoxybutan-2-ones 4. An insight into the selection mechanism was gained by temperature dependent measurements on the irradiation of the dicinnamates 10a-d, since the corresponding Eyring diagram discloses strictly linear functions as well as an isoselective relationship. Diol 8a turned out to be a structurally optimized auxiliary in terms of chiral induction and product crystallization and was also successfully applied in the first asymmetric photodimerization of 2-indenecarboxylic acid esters. Indeed, in this case excellent diastereoselectivities were achieved, too, but head-to-tail dimers 16a and 16b were formed predominantly. Diesters 11a and 16a were converted by standard procedures into the desired enantiopure 1,4-diphosphane 22 and 1,5-diphosphane 27. Furthermore, the hitherto unknown absolute configuration of δ-truxinic acid was elucidated from a single crystal X-ray structure analysis of 11a.

Full text of DOI:10.1021/jo960556y

J . Org. Chem. 1996, 61, 6127-6135
6127
In vestiga tion s of th e Asym m etr ic In tr a m olecu la r [2 + 2]
P h otocycloa d d ition a n d Its Ap p lica tion a s a Sim p le Access to
Novel C2-Sym m etr ic Ch ela tin g Bisp h osp h a n es Bea r in g a
Cyclobu ta n e Ba ck bon e
Dieter Haag and Hans-Dieter Scharf*
Institut fu¨r Organische Chemie der Rheinisch Westfa¨lischen Technischen Hochschule Aachen,
Professor-Pirlet-Strasse 1, D-52056 Aachen, Germany
Received March 26, 1996X
The asymmetric intramolecular [2 + 2] photocycloaddition of R,â-enoates was evaluated as a simple
access to the novel C2-symmetric bisphosphanes 22 and 27 possessing a cyclobutane backbone. A
source of different chiral auxiliaries for investigations of the photochemical key step was provided
by the transacetalization of dialkyl tartrates 3 with the corresponding 3,3-dialkoxybutan-2-ones 4.
An insight into the selection mechanism was gained by temperature dependent measurements on
the irradiation of the dicinnamates 10a -d , since the corresponding Eyring diagram discloses strictly
linear functions as well as an isoselective relationship. Diol 8a turned out to be a structurally
optimized auxiliary in terms of chiral induction and product crystallization and was also successfully
applied in the first asymmetric photodimerization of 2-indenecarboxylic acid esters. Indeed, in
this case excellent diastereoselectivities were achieved, too, but head-to-tail dimers 16a and 16b
were formed predominantly. Diesters 11a and 16a were converted by standard procedures into
the desired enantiopure 1,4-diphosphane 22 and 1,5-diphosphane 27. Furthermore, the hitherto
unknown absolute configuration of δ-truxinic acid was elucidated from a single crystal X-ray
structure analysis of 11a .
Ch a r t 1
In tr od u ction
The conformational properties of ligands are well-
known to influence the reactivity and selectivity of
transition metal catalysts.1 This is particularly evident
in the enantiodifferentiating hydrogenation catalyzed by
rhodium(I) complexes bearing chelating bisphosphanes.
By comparison of DIOP2 and its carbocyclic analogues,3
the effect of the conformational properties of the ligand
backbone on the seven-membered rhodium(I) chelate
ring which may adopt two extremely different conforma-
tions with a respective enantiomorphous arrangement of
the P-phenyl groups3b,4 has been clearly demonstrated.
However not many efforts have been made on tuning
catalytic properties by variation of the substitution
pattern of the carbocyclic framework. The promising
selectivities achieved in asymmetric rhodium(I)-catalyzed
hydrogenations utilizing C4DIOP (1)3a (Chart 1) and its
recently synthesized analogue MOCBP (2)5 as chelating
ligands prompted us to elaborate a new access to enan-
tiopure chelating bisphosphanes bearing a cyclobutane
backbone.
tereoselectivity, this approach is structurally restricted
to the employment of ketene derivatives for the cyclobu-
tane formation. Such limitations should be overcome by
the use of an asymmetric [2 + 2] photocycloaddition, as
it renders possible two orthogonal retrosynthetic scissions
which are presented in Scheme 1. For our preliminary
synthetic studies, the intramolecular variant of route A
seemed to be most promising. Previous investigations
had already revealed erythritol derivatives to be suitable
chiral auxiliaries for the intramolecular photodimeriza-
tion of cinnamic acid esters.7 However, neither 2,3-O-
isopropylidenerythritol nor 2,3-di-O-methylerythritol met
all requirements for a synthetic application. Indeed, with
the 1,4-dicinnamate of the latter one the corresponding
(+)-δ-truxinate formed with a diastereoselectivity of 85%,
but all attempts to isolate this diastereomer failed.7
Retr osyn th etic An a lysis. Although the synthesis of
MOCBP (2) via an asymmetric thermal [2 + 2] cycload-
dition5,6 is straightforward and proceeds with high dias-
Syn th esis of Ch ir a l Au xilia r ies for th e P h oto-
d im er iza tion . With regard to these results, we expected
the tartaric acid derived dioxanes 8a and 8b8 to be
optimized auxiliaries for the asymmetric [2 + 2] photo-
cycloaddition, since the essential requirements are present
in their structure. The stabilization of the gauche
conformation of the hydroxymethylene groups is quite
similar to that in 2,3-di-O-methylerythritol. Moreover,
due to its well-defined conformation, a six-membered ring
should promote crystallization and therefore purification
of the diastereomeric cycloaddition products. The re-
X Abstract published in Advance ACS Abstracts, August 15, 1996.
(1) (a) Ojima, I. Catalytic Asymmetric Syntheses; VCH Publishers:
Weinheim, 1993. (b) Noyori, R. Asymmetric Catalysis in Organic
Syntheses, J . Wiley & Sons: New York, 1994.
(2) (a) Kagan, H. B.; Dang, T. P. J . Am. Chem. Soc. 1972, 94, 6429.
(b) Kagan, H. B. In Comprehensive Organometallic Chemistry; Wilkin-
son, G., Ed.; Pergamon Press, Oxford, 1982; Vol. 8, p 463.
(3) (a) Aviron-Violet, P.; Colleuille, Y.; Varagnat, J . J . Mol. Catal.
1979, 5, 41. (b) Glaser, R.; Geresh, S.; Twaik, M. Isr. J . Chem. 1980,
20, 102.
(4) (a) Brown, J . M.; Chaloner, P. A. J . Am. Chem. Soc. 1978, 100,
4321. (b) Brown, J . M.; Chaloner, P. A.; Glaser, R.; Geresh, S.
Tetrahedron 1980, 36, 815.
(5) Morimoto, T.; Nakajima, M.; Achiwa, K. Tetrahedron: Asym-
metry 1995, 6, 75.
(6) Ahmad, S. Tetrahedron Lett. 1991, 32, 6997.
(7) Green, B. S.; Hagler, A. T.; Rabinsohn, Y.; Rejto¨, M Isr. J . Chem.
1976/77, 15, 124.
(8) Berens, U.; Leckel, D.; Oepen, S. C. J . Org. Chem. 1995, 60, 8204.
S0022-3263(96)00556-7 CCC: $12.00 © 1996 American Chemical Society

6128 J . Org. Chem., Vol. 61, No. 18, 1996
Haag and Scharf
Sch em e 1
a reaction time of 12 h proved to be essential for the
attainment of a good diastereoselectivity (Table 1). The
main diastereomer 5a could be easily obtained by crys-
tallization from the crude reaction mixture. Column
chromatography of the mother liquor furnished an in-
separable 62:38 mixture of 1,4-dioxanes 5a and 6a as well
as a pure sample of 1,4-dioxane 7a . The coupling
constant of 8.1 Hz between the two dioxane ring protons
(determined from the 13C-satellite) in 6a indicates a
remarkable deviation from the expected 1,2-trans-di-
axial relationship. This phenomenon may be rationalized
by a preference for a twist-boat conformation (Scheme
3) of the dioxane ring which has already been shown to
be predominant in certain R-L-sorbopyranose deriva-
tives.10 Moreover, a twist-boat conformation possibly
compensates for the destabilization caused by the ano-
meric effect in the chair conformation of 6a . This
assumption is consistent with the experimental results
which rank the dioxanes 6a and 6b to be more stable
than 7a and 7b.
With the diasteromerically pure ester 5a as starting
material, a clearly improved yield of the desired diol 8a
was achieved (Scheme 4). The minor diastereomer 9a
was obtained by reduction of a 62:38 mixture of diesters
5a and 6a and subsequent chromatographical separation.
Reduction of a 96:4 mixture of diesters 5b and 6b yielded,
upon crystallization of the crude product, diol 8b. The
minor compound 9b was isolated from the mother liquor.
Ster eoselective In tr a m olecu la r [2 + 2] P h otocy-
cloa d d ition of Dicin n a m a tes a n d Di-2-in d en oa tes.
As the asymmetric photodimerization represents the
crucial step in our new access to C4DIOP-related ligands,
it was important to detect the relevant factors influencing
its selectivity. For this purpose the dicinnamates 10a -d
were prepared from the corresponding diols by standard
methodology. They were irradiated at different temper-
atures ranging from -75 to +45 °C in toluene as solvent
to give the anticipated mixtures of the respective (+)-δ-
11a -d , (-)-δ-12a -d , â-13a -d and neotruxinates 14a -c
(Scheme 5). The relative configuration of δ-truxinate 11a
was established by means of single crystal X-ray analy-
sis.11a Upon conversion into the corresponding dimethyl
ester with SOCl2 in boiling methanol, it was shown to
be a derivative of (+)-dimethyl δ-truxinate.12 Thus, we
were enabled to elucidate the correct absolute configu-
ration of (+)-δ-truxinic acid, which turned out to be
opposite of that previously assumed by Green.7 The
ratios of the diastereomeric cyclobutane products were
determined by 13C-NMR spectroscopy. In all cases the
formation of 14a -c was negligible and could only be
established after chromatographical workup.
Ta ble 1. Effect of Rea ction Tim e on Tr a n sa ceta liza tion
of Dia lk yl Ta r tr a tes (3) w ith Cor r esp on d in g
3,3-Dia lk oxybu ta n -2-on es (4)
R
t (h)
5:6:7
yield (%)
a : Mea
4
12
4
81:12:7
94:5:1
72:21:8
96:4:-
-
73 (5a )b
91 (md)c
88 (md)c
b: Etd
12
a
b
Reaction conditions: 60 °C, 40 mmHg. Diastereomerically
c
pure on crystallization. Ratio of diastereomers remained un-
changed after distillation. Reaction conditions: 70 °C, 70 mmHg.
d
cently described transacetalization of diethyl tartrate 3b
with 3,3-dialkoxybutan-2-ones 4a and 4b8,9 represents
the key step in the synthesis of the diols 8a and 8b. In
the course of our own investigations on the conversion
with acetal 4b, we established the necessity of prolonged
reaction times for the attainment of high diastereomeric
excesses. Quenching the reaction just after complete
addition of 4b afforded a mixture of all three possible
diastereomeric 1,4-dioxanes, 5b, 6b, and 7b, with only a
moderate degree of stereoselectivity (Table 1 and Scheme
2). Separation of these three diastereomers was per-
formed by subjecting this mixture to column chromatog-
raphy. With a pure sample of 1,4-dioxane 6b in hand
we were able to refute the formerly made assumption
that due to anomeric effects the formation of the diacetal
7b with a 1,2-cis relationship should be more favored.
Upon prolonged reaction time, 7b even completely van-
ished and the reported 96:4 product distribution was
attained.
For the synthesis of 8a we intended to circumvent the
disadvantages involved in the BF3-mediated transacetal-
ization of diethyl tartrate 3b with 4a , which, regardless
of the reaction time, proceeded only with incomplete
conversion and moderate selectivity.8 A striking im-
provement was achieved by employing dimethyl tartrate
3a instead of 3b and slightly modifying the reaction
conditions already applied for the synthesis of 5b. Again,
The Eyring plot (Figure 1) reveals two typical features
of the asymmetric intramolecular [2 + 2] photocycload-
dition. First, the ln P values (P ) [11]/[12] ) k(excess
δ-truxinate)/k(minor δ-truxinate)) are found to be linearly
dependent on the reciprocal of temperature in the whole
temperature region investigated. On the basis of the
principle of isoinversion,13 this is equivalent to the
existence of a single relevant partial step generating
stereoselectivity in the cyclobutane formation. Further-
more, variation of the auxiliary discloses an isoselective
relationship, as all four extrapolated curves intersect in
(9) For other publications dealing with the transacetalization of
vicinal diols with R-dicarbonyl compounds see: (a) Ley, S. V.; Leslie,
R.; Tiffin, P. D.; Woods, M. Tetrahedron Lett. 1992 , 33, 4767. (b) Ley,
S. V.; Boons, G.-J .; Leslie, R.; Woods, M.; Hollinshead, D. M. Synthesis
1993, 689. (c) Fujioka, H.; Kitagawa, H.; Nagatomi, Y.; Kita, Y.
Tetrahedron: Asymmetry 1995, 6, 2113. (d) Montchamp, J .-L.; Tian,
F.; Hart, M. E.; Frost, J . W. J . Org. Chem. 1996, 61, 3897.
(10) Costanzo, M. J .; Almond, H. R.; Gauthier, A. D.; Maryanoff, B.
E. Tetrahedron Asymmetry 1994, 5,2459.
(11) (a) Haag, D.; Scharf, H.-D.; Raabe, G. Acta Crystallogr., Sect.
C, to be submitted. (b) Haag, D.; Scharf, H.-D.; Raabe, G. Acta
Crystallogr., Sect. C, to be submitted.
(12) Stoermer, B.; Bacher, F. Chem. Ber. 1922, 55, 1860.

Asymmetric Intramolecular [2 + 2] Photocycloaddition
J . Org. Chem., Vol. 61, No. 18, 1996 6129
Sch em e 2
Sch em e 3
Sch em e 4a
F igu r e 1. Eyring diagram for the competitive formation of
diastereomeric δ-truxinates in the asymmetric intramolec-
ular [2 + 2] photocycloaddition of dicinnamtes 10a -d (see
Scheme 5).
(Scheme 6). This result is in line with the observations
made on the intermolecular photosensitized [2 + 2]
photocycloaddition.16 Concerning the competitive forma-
tion of δ-truxinates 11 and 12 versus â-truxinate 13, a
similiar temperature dependent relationship seems to
exist (Table 2). Indeed, a diminishing selectivity for the
latter one with decreasing temperature is observed, but
the diastereomeric ratios determined by 13C-NMR spec-
troscopy are not sufficiently exact for a quantitative
evaluation. Some inaccuracy arises from the removal of
C2-symmetry in the â-truxinates 13 causing a double set
of 13C-NMR signals the NOE and spin relaxation effects
of which differ from those of the δ-truxinates 11 and 12.
The strong influence of the diacetal moiety on the
diastereoselectivity discloses two essential properties of
a structurally optimized auxiliary for the intramolecular
[2 + 2] photocycloaddition. A stabilization of the 1,4-
dioxane ring chair conformation due to a double anomeric
effect caused by the 2,3-trans-diaxial relationship of the
alkoxy substituents in 10a and 10b and a minimal
number of degrees of freedom (comparison of methyl
acetals 10a and 10c vs ethyl acetals 10b and 10d ) are
necessary to “fix” an advantageous gauche conformation
of the (cinnamoyloxy)methylene groups. As a conse-
quence of these requirements 10d did not undergo any
[2 + 2] cycloaddition upon irradiation at 45 °C.
a
Yields in parantheses refer to the corresponding diastereomer
contained in the starting material.
Sch em e 5a
Next, we expanded our investigations on the intramo-
lecular [2 + 2] photocycloaddition of 2-indenecarboxy-
a
Key: (a) 2.2 equiv of PhCHCHCOCl, cat. DMAP, pyridine,
b
CH2Cl2; (b) hν, T, 60 h, toluene. Assignment of the absolute
configuration of the cyclobutane moiety was arbitrary.
(13) (a) Buschmann, H.; Scharf, H.-D.; Hoffmann, N.; Plath, M. W.;
Runsink, J . J . Am. Chem. Soc. 1989, 111, 5367. (b) Buschmann, H.;
Scharf, H.-D.; Hoffmann, N.; Esser, P. Angew. Chem. 1991, 103, 480;
Angew. Chem., Int. Ed. Engl. 1991, 30, 477.
(14) (a) Exner, O.; Giese, B. Angew. Chem. 1978, 90, 816; Angew.
Chem., Int. Ed. Engl. 1978, 17, 775. (b) Giese, B. Acc. Chem. Res. 1984,
17, 438.
(15) (a) Loutfy, R. O.; De Mayo, P. J . Am. Chem. Soc. 1977, 99, 3559.
(b) Hastings, D. J .; Weedon, A. C. J . Am. Chem. Soc. 1991, 113, 8525.
(16) Hoffmann, N.; Buschmann, H.; Raabe, G.; Scharf, H.-D. Tet-
rahedron 1994, 50, 11167.
a narrow region close to 600 K. According to Giese,14 this
fact is interpreted as evidence for the diastereoselection
to be introduced in all four cases on the basis of the same
mechanism. From these facts we conclude the formation
of the 1,4-diradical intermediate to be the dominant part
in the selection step, whereas the competition between
cyclization and fragmentation is only of minor importance

6130 J . Org. Chem., Vol. 61, No. 18, 1996
Haag and Scharf
Sch em e 6a
Sch em e 7a
a
Key: (a) 2-indenecarboxylic acid, DCC, cat. DMAP, CH2Cl2;
(b) hν, T, 36 h, toluene.
namates exclusively yielded head-to-head dimers, in the
cycloaddition of their bridged analogues 15a and 15b,
head-to-tail dimerization gained significantly in impor-
tance (Scheme 7 and Table 3). Regardless of the auxil-
iary and the temperature, syn-head-to-tail dimer 16, the
structure of which was determined from a single crystal
X-ray analysis of 16a ,11b represents the main isomer.
Besides, the formation of nearly equal amounts of two
further isomers, anti-head-to-head dimer 17 and syn-
head-to-head dimer 18, was observed. Their structures
were deduced from NMR spectroscopical measurements.
The coupling constant of 9.1 Hz between the two cyclobu-
tane ring protons in 18a clearly indicates their vicinal
relationship. Furthermore, due to anisotropic shielding
of the aryl groups, the signals of the methylene protons
adjacent to the aryl group in syn-additon products 16a
and 18a are shifted to higher field (0.27-0.71 ppm) as
compared with anti-addition product 17a . On the con-
trary, in the latter the cyclobutane ring protons are
shifted significantly to higher field (0.70-0.82 ppm).
The excellent diastereoselectivities achieved in the
anti-head-to-head addition as well as the syn-head-to-
tail addition are in accordance with the good inductions
observed for δ-truxinate formation. Therefore, we as-
sume the formation of 11, 16, and 17 to be uniformly
controlled by the same conformation of the diol moiety.
The absolute configurational assignment of the cyclobu-
tane ring of 17 has been made according to this assump-
tion. Obviously, among the factors influencing the
selectivity of cyclobutane formation, not only the auxil-
iary plays an important role but also the conformational
properties of the enoate itself. Looking at suitable
precursor conformations for the intramolecular cyclodimer-
ization of 15 (illustrated in Scheme 8), one can see that
the s-cis conformer leads to anti-head-to-head addition,
whereas the s-trans conformer favors syn-head-to-tail
addition.19 Semiempirical calculations on the corre-
sponding methyl esters as model compounds (Table 4)
tend to support this interpretation, which requires a
distinct preference of the s-cis conformation in the case
of cinnamates. Moreover, in particular the s-cis precur-
a
The biradical mechanism illustrated in this scheme is adapted
from that assumed for the [2 + 2] photocycloaddition of enones to
olefines.15 Z/E-isomerization was established while controlling
b
the conversion by NMR spectroscopy. c To simplify the illustration
d
only one of the possible isomers and rotamers is shown. The
generation of the 1,4-biradicals proceeds presumably via exciplex
formation.15a e 14 may be formed from rotamers of p r e-11 and
p r e-12.
Ta ble 2. Effect of Tem p er a tu r e a n d Au xilia r y on
Asym m etr ic In d u ction in th e In tr a m olecu la r [2 + 2]
P h otocycloa d d iton of Dicin n a m a tes (10a -d )
T (°C)
-60
substrate
11:12:13
10a
10b
10c
10d
10a
10b
10c
10d
27.0:1:4.5
11.7:1:5.6
5.8:1:2.4
4.4:1:2.0
6.5:1:2.2
3.6:1:2.2
2.4:1:1.7
1.8:1:1.0
+8
lates, which are already known to be suitable substrates
for the achiral variant of this reaction.17 The di-2-
indenecarboxylates 15a and 15b were prepared following
the esterification protocol of Neises and Steglich.18
Lacking any possibility of cis-trans isomerization, the
cyclobutane formation required remarkably less reaction
time than in the case of the corresponding dicinnamates
10a -d and proceeded with almost quantitative yield.
Even more dramatic is the difference in the regiochemical
course of the reaction. Whereas irradiation of dicin-
(17) (a) Lewis, F. D.; Quillen, S. L.; Hale, P. D.; Oxman, J . D. J .
Am. Chem. Soc. 1988, 110, 1261. (b) Takagi, K.; Itoh, M.; Usami, H.;
Imae, T.; Sawaki, Y. J . Chem. Soc. Perkin Trans. 2 1994, 1003.
(18) Neises, B.; Steglich, W. Angew. Chem. 1978, 90, 556; Angew.
Chem., Int. Ed. Engl. 1978, 17, 522.

Asymmetric Intramolecular [2 + 2] Photocycloaddition
J . Org. Chem., Vol. 61, No. 18, 1996 6131
Sch em e 8
Sch em e 9a
Ta ble 3. Effect of Tem p er a tu r e a n d Au xilia r y on
Asym m etr ic In d u ction in th e In tr a m olecu la r [2 + 2]
P h otocycloa d d iton of Di-2-in d en oa tes (15a ,b)
T (°C)
-70
substrate
16:17:18
15a
15b
15a
15b
2.6:1:1.1
1.5:1:0.9
2.3:1:1.2
1.6:1:1.0
-40
Ta ble 4. Ca lcu la ted En er gy Differ en ces betw een s-cis
a n d s-tr a n s Con for m er s of Meth yl Cin n a m a te a n d Meth yl
2-In d en oa te
∆Ea (kJ mol-1
)
compound
AM1
MNDO
methyl cinnamate
methyl 2-indenoate
-1.92
-0.03
-3.43
+0.21
a
∆E ) E(s-cis) - E(s-trans).
a
Key: (a1) hν, -60 °C, 60 h, toluene; (a2) hν, -70 °C, 36 h,
sor conformation of 15 exhibits unfavorable nonbonded
interactions between the protons of the two methylene
groups. On the contrary, for the s-cis conformation of
the corresponding dicinnamate 10, such a destabilizating
effect can be excluded.
toluene; (b) LiAlH4, THF; (c) TsCl, cat. DMAP, pyridine, CH2Cl2;
(d) Li[PPh2(BH3)] (23), THF/DMF; (e) HBF4OMe2; ∆, CH2Cl2.
b
Overall recovery of 8a : 61%. c Overall recovery of 8a : 45%.
or 16a in good to excellent yields employing established
procedures. Particularly, the introduction of the diphen-
ylphosphane group via the phosphane-borane adducts
21 and 26 proved to be a convenient method. It is
noteworthy, that, in our hands, the protocol according
to Le Corre20 involving the in-situ generation of 23 from
triphenylphosphane-borane adduct and lithium resulted
in alternating, but in any case definitely lower, yields
for the phosphanation step. Moreover, the use of DMF
as cosolvent21 turned out to be an essential factor for
optimized reaction conditions. Finally, the complete
protolytic decomplexation21 of 21 and 26 to the free 1,4-
diphosphane 22 and 1,5-diphosphane 27, respectively,
was accomplished at elevated temperature by constantly
removing the liberated diborane.
Syn t h esis of Cyclob u t a n e-Ba sed C2-Sym m et r ic
Liga n d s. Concerning the influence of the diacetal
moiety of the auxiliary and the temperature, the above
observations clearly exhibit the same tendencies for the
intramolecular cylodimerization of dicinnamates 10a -d
(Table 2, Figure 1) as well as the di-2-indenoates 15a and
15b (Table 3). In every case, diol 8a turns out to be the
superior auxiliary, and the discrimination between the
selectivities attainable with the auxiliaries 8a and 8b
respectively increases with decreasing temperature. So,
we focused our attention on the compounds 10a and 15a
to elaborate a preparatively useful route to the desired
enantiopure cyclobutanes 22 and 27 (Scheme 9). Ir-
radiation of 10a at low temperature and subsequent
crystallization provided diastereomerically pure δ-truxi-
nate 11a in good yield. Preparation and purification of
cyclobutane 16a were performed in an analogous manner.
Since this compound is hardly soluble in any common
solvent and therefore its separation is easily feasible even
on a multigram scale, we could tolerate the modest
regioselectivity achieved in the irradiation of 15a .
So far, the enantiopure diols 19 and 24 as well as the
aspired diphosphanes 22 and 27 were prepared from 11a
Con clu sion s
We have elaborated a versatile asymmetric synthetic
route to new C2-symmetrical diphosphanes possessing a
strongly substituted cyclobutane backbone. Representing
the crucial step in this protocol, the asymmetric intramo-
lecular [2 + 2] photocycloaddition was investigated in
more detail to unveil the relevant factors determining
its selectivity. On the basis of these results, diol 8a is
featured as a structurally optimized auxiliary, permitting
(19) The equilibrium between s-cis and s-trans conformers of R,â-
enal complexes is also discussed to be a relevant factor determining
the selectivity of catalytic Diels-Alder reactions: (a) Birney, D. M.;
Houk, K. N. J . Am. Chem. Soc. 1990, 112, 4127. (b) Corey, E. J .; Loh,
T.-P.; Roper, T. D.; Azimioara, M. D.; Noe, M. C. J . Am. Chem. Soc.
1992, 114, 8290.
(20) Brisset, H.; Gourdel, Y.; Pellon, P.; Le Corre, M. Tetrahedron
Lett. 1993, 34, 4523.
(21) McKinstry, L.; Livinghouse, T. Tetrahedron Lett. 1994, 35, 9319.

6132 J . Org. Chem., Vol. 61, No. 18, 1996
Haag and Scharf
- MeO)+. 1H-NMR (CDCl3, 300 MHz): δ 1.36 (s, 6), 3.33 (s,
6), 3.77 (s, 6), 4.54 (s, 2, 13C-satellite: dd, 1J C,H ) 150.5 Hz, 3J
) 10.0 Hz). 13C-NMR (75 MHz, CDCl3): δ 17.33, 48.46, 52.52,
68.76, 99.22, 168.44. Anal. Calcd for C12H20O8: C, 49.31; H,
6.90. Found: C, 49.37; H, 6.97.
us to perform the cyclodimerization of cinnamates and
2-indenoates with excellent diastereoselectivities on a
preparative by useful multigram scale.
Current studies, in the group of Selke,22 are aimed at
uncovering the potential of diphosphanes 22 and 27 and
their close relatives as ligands in transition- metal-
catalyzed enantiodifferentiating syntheses. Results on
the conversion of diesters 11a and 16a into the corre-
sponding cyclobutane-based TADDOL analogues23 and
their application in asymmetric syntheses will be re-
ported soon.
(2R,3R,5S,6S)-5,6-Dim eth oxy-5,6-dim eth yl[1,4]dioxan e-
2,3-d ica r boxylic Acid Dim eth yl Ester (6a ). [R]20D: -2.9°
(c ) 1.05, CHCl3). 1H-NMR (CDCl3, 500 MHz): δ 1.39 (s, 6),
3.39 (s, 6), 3.77 (s, 6), 4.83 (s, 2, 13C-satellite: dd, 1J C,H ) 152.2
3
Hz, J ) 8.1 Hz). 13C-NMR (75 MHz, CDCl3): δ 18.16, 49.26,
52.40, 70.15, 100.36, 169.85. Anal. Calcd for C12H20O8: C,
49.31; H, 6.90. Found: C, 49.38; H, 6.90.
(2R,3R,5r ,6s)-5,6-Dim eth oxy-5,6-d im eth yl[1,4]d ioxa n e-
2,3-d ica r boxylic Acid Dim eth yl Ester (7a ). [R]20D: -14.5°
(c ) 0.94, CHCl3). IR (CHCl3): 3015, 2839, 1751, 757 cm-1
.
Exp er im en ta l Section
MS (70 eV): m/z 261 (M - MeO)+. 1H-NMR (CDCl3, 300
MHz): δ 1.32, 1.63 (2 s, 6), 3.36, 3.44 (2 s, 6), 3.76, 3.79 (2 s,
6), 4.50, 4.54 (2 d, 2, 3J ) 9.9 Hz). 13C-NMR (75 MHz,
CDCl3): δ 16.93, 17.57, 48.89, 50.06, 52.45, 52.59, 68.64, 72.50,
99.08, 100.03, 167.94, 168.69. Anal. Calcd for C12H20O8: C,
49.31; H, 6.90. Found: C, 49.30; H, 6.97.
Gen er a l. Unless otherwise noted, materials were obtained
from commercial suppliers and used without further purifica-
tion. THF was dried by the sodium-benzophenone method
immediately prior to use. CH2Cl2 was distilled from LiAlH4
in order to remove water and ethanol. Dry DMF was obtained
by distillation from CaH2. GC analyses were performed on a
HP 5890 series II gas chromatograph equipped with a FFAP
column (25 m × 0.32 mm), a flame ionization detector, and a
HP 3396 A integrator. TLC was conducted with plates
(2R,3R,5R,6R)-5,6-Dieth oxy-5,6-d im eth yl[1,4]d ioxa n e-
2,3-d ica r boxylic Acid Dieth yl Ester (5b). b1: This com-
pound was prepared in analogy to the procedure for 5a from
155 g of L-(+)-diethyl tartrate (3b) (0.75 mol), 3 g of p-
toluenesulfonic acid, and 253 g of 3,3-diethoxybutan-2-one
(4b)8 (1.58 mol) at 60 °C/40 mmHg. After the workup
procedure and distillation according to ref 8, 230 g of a 96:4
mixture of diastereomeric dioxanes 5b and 6b (88% based on
3b) was obtained.
b2: A 71:21:8 mixture of diasteromeric 1,4-dioxanes 5b, 6b,
and 7b was produced by the same technique reported above
from 5.00 g of 3b (24.2 mmol), 0.10 g of p-toluenesulfonic acid,
and 8.14 g of 4b (50.8 mmol). The reaction was interrupted
immediately after the addition of 4b by addition of 0.5 g of
K2CO3. The reaction mixture was stirred for another hour,
filtered, and distilled to give 7.65 g of a mixture of 1,4-dioxanes
(91% based on 3b). 1.04 g of this slightly yellow oil was
subjected to column chromatography on 400 g of silica gel with
7:1 hexane-ethyl acetate to afford in order of increasing
polarity 201 mg of 6b, 207 mg of a fraction containing a 95:5
mixture of 5b and 6b, 508 mg of 5b and 77 mg of 7b.
5b. [R]20D: -111.5° (c ) 1.14, CHCl3). IR (CHCl3): 2980,
2898, 1747, 1188 cm-1. MS (70 eV): m/z 303 (M - EtO)+. 1H-
NMR (CDCl3, 500 MHz): δ 4.50 (13C-satellite: dd, 1J C,H ) 151.1
Hz, 3J ) 10.1 Hz). Remaining NMR data are in accordance
with ref 8. Anal. Calcd for C16H28O8: C, 55.16; H, 8.10.
Found: C, 55.50; H, 8.40.
precoated with kieselgel 60 F254
. Unless otherwise noted,
detection was first by UV (254 nm) and then charring with a
solution of 1.0 g vanillin in 250:25:10 methanol-acetic acid-
sulfuric acid. After extraction of aqueous solutions the com-
bined organic layers were dried over MgSO4. Evaporation of
solvents was accomplished with a rotary evaporator. Melting
points (Pyrex capillary) are uncorrected.
(2R,3R,5R,6R)-5,6-Dim eth oxy-5,6-dim eth yl[1,4]dioxan e-
2,3-d ica r boxylic Acid Dim eth yl Ester (5a ). A 500 mL flask
was fitted with a pressure-equalized dropping funnel and a
50 cm Vigreux column which was connected to a gas outlet
leading to a condensing trap. The flask was charged with 134
g of L-(+)-dimethyl tartrate (3a ) (0.75 mol) and 3 g of
p-toluenesulfonic acid. After being heated to 70 °C, the trap
was connected with a water aspirator and the pressure in the
flask was adjusted to 70 mmHg. Then, 209 g of 3,3-dimethoxy-
butan-2-one (4a )8 (1.58 mol) was added to the reaction mixture
within 4 h. At this point of the reaction GC analysis revealed
complete consumption of 3a and a product distribution of 5a ,
6a , and 7a in a ratio of 81:12:7. After stirring for additional
8 h, 12 g of K2CO3 was added. As soon as the temperature
had dropped below 60 °C the viscous reddish brown mixture
was disolved in 250 mL of CHCl3 and stirring was continued
for another hour. This suspension was poured on 200 mL of
water, the phases were separated, and the aqueous layer was
extracted twice with 250 mL of CHCl3. The combined organic
phase was dried, filtered, and concentrated under reduced
pressure. The product ratio of 5a , 6a , and 7a was determined
by GC analysis to be 94:5:1. The obtained brown mass was
dissolved in a minimum of ether, and pentane was added until
the solution became turbid. On standing in the refrigerator,
the product crystallized to give 160 g of 5a (73% based on 3a )
as colorless crystals. The filtrate was concentrated and
distilled under high vacuum. The fraction boiling at 106-109
°C/0.01 mbar was collected to furnish 26.8 g of 1,4-dioxanes
5a , 6a , and 7a as a 57:36:7 mixture of diastereomers. This
material was subjected to column chromatography on 500 g
of silica gel with 2:1 hexane-ethyl acetate to afford 22.1 g of
a 62:38 mixture of diastereomers 5a and 6a (analytical data
of 6a refer to this mixture). Further elution with ether yielded
1.68 g of 7a as a colorless oil. Detection was performed by
charring with a solution of ammonium molybdate(VI) tetrahy-
drate in 10% aqueous H2SO4.
(2R,3R,5S,6S)-5,6-Dieth oxy-5,6-d im eth yl[1,4]d ioxa n e-
2,3-d ica r boxylic Acid Dieth yl Ester (6b). [R]20D: +28.9°
(c ) 0.91, CHCl3). IR (CHCl3): 2981, 2898, 1752, 757 cm-1
.
MS (70 eV): m/z 303 (M - EtO)+. 1H-NMR (CDCl3, 500
3
3
MHz): δ 1.21 (t, 6, J ) 7.1 Hz), 1.28 (t, 6, J ) 7.1 Hz), 1.41
2
(s, 6), 3.57, 3.93 (2 dq, 4, | J | ) 8.9 Hz), 4.17, 4.23 (2 dq, 4,
| J | ) 10.8 Hz), 4.82 (s, 2, 13C-satellite: dd, J C,H ) 156.6 Hz,
3J ) 10.4 Hz). 13C-NMR (75 MHz, CDCl3): δ 14.03, 15.54,
19.18, 56.59, 61.44, 71.21, 100.37, 169.17. Anal. Calcd for
C16H28O8: C, 55.16; H, 8.10. Found: C, 55.54; H, 8.36.
(2R,3R,5r ,6s)-5,6-Diet h oxy-5,6-d im et h yl[1,4]d ioxa n e-
2,3-d ica r boxylic Acid Dieth yl Ester (7b). [R]20D: -24.6°
2
1
(c ) 1.58, CHCl3). IR (CHCl3): 2981, 2904, 1751, 1200 cm-1
.
MS (70 eV): m/z 303 (M - EtO)+. 1H-NMR (CDCl3, 300
MHz): δ 1.21, 1.28 (2 t, 6, 3J ) 7.1 Hz), 1.30 (t, 6, 3J ) 7.2
2
Hz), 1.33, 1.62 (2 s, 6), 3.61, 3.66 (2 dq, 2, | J | ) 9.7 Hz), 3.68,
2
3.88 (2 dq, 2, | J | ) 9.2 Hz), 4.21, 4.23 (2 q, 4), 4.50, 4.55 (2 d,
3
2, J ) 10.1 Hz). 13C-NMR (75 MHz, CDCl3): δ 14.01 (2 C),
15.53, 15.63, 17.91, 18.97, 57.00, 58.28, 61.50 and 61.58, 68.76,
72.67, 99.27, 100.03, 167.67, 168.49. Anal. Calcd for
C16H28O8: C, 55.16; H, 8.10. Found: C, 55.33; H, 8.20.
(2S,3S,5R,6R)-2,3-Bis(h yd r oxym eth yl)-5,6-d im eth oxy-
5,6-d im eth yl[1,4]d ioxa n e (8a ). a 1: To a stirred suspension
of 24.1 g of LiAlH4 (0.636 mol) in 400 mL of dry THF was added
a solution of 155 g of diester 5a (0.530 mol) in 250 mL of THF
in portions at a rate maintaining gentle reflux. Afterwards,
the reaction mixture was heated at reflux for 3 h. Hydrolysis
of the excess LiAlH4 was accomplished by careful additon of
10% KOH (∼50 mL) just to the point that the gray slurry
5a . Mp: 107 °C. [R]20D: -110.4° (c ) 1.13, CHCl3). IR
(KBr): 2993, 2841, 1738, 1364 cm-1. MS (70 eV): m/z 261 (M
(22) Ru¨diger Selke, Max-Planck-Gesellschaft AG “Asymmetrische
Katalyse” an der Universita¨t Rostock, Germany.
(23) (a) Seebach, D.; Plattner, D. A.; Beck, A. K.; Wang, Y. M.;
Hunziker, D.; Petter, W. Helv. Chim. Acta 1992, 75, 2171. (b) Ito, Y.
N.; Ariza, X.; Beck, A. K.; Bohac, A.; Ganter, C.; Gawley, R. E.; Kuhnle,
F. N. M.; Tuleja, J .; Wang, Y. M.; Seebach, D. Helv. Chim. Acta 1994,
77, 2071.

Asymmetric Intramolecular [2 + 2] Photocycloaddition
J . Org. Chem., Vol. 61, No. 18, 1996 6133
turned white. Then, the reaction mixture was heated at reflux
for another hour. After filtration the white inorganic precipi-
tate was extracted twice with 400 mL of boiling 95:5 THF-
water. The combined THF solution was dried, filtered, and
evaporated to give 126 g of a solid white residue. This residue
was redissolved in a minimum of boiling ether. On standing
in the refrigerator diol 8a precipitated to give 119 g of colorless
crystals (95% based on 5a ).
7.29-7.48 (m, 10), 7.63 (d, 2). 13C-NMR (75 MHz, CDCl3): δ
17.52, 48.04, 63.79, 67.80, 99.06, 117.52, 128.15, 128.83,
130.35, 134.23, 145.37, 166.58. Anal. Calcd for C28H32O8: C,
67.73; H, 6.50. Found: C, 67.69; H, 6.64.
(2S,3S,5R,6R)-2,3-Bis(((in den e-2-car bon yl)oxy)m eth yl)-
5,6-d im eth oxy-5,6-d im eth yl[1,4]d ioxa n e (15a ). To a solu-
tion of 22.9 g of 2-indenecarboxylic acid24 (143 mmol), 1.0 g of
DMAP (8.2 mmol), and 15.6 g of diol 8a (66.0 mmol) in 100
mL of CH2Cl2 was added 31.7 g of DCC (154 mmol) in 50 mL
of CH2Cl2 at a rate maintaining the temperature below 30 °C.
After stirring for 18 h the reaction mixture is filtered through
Celite and evaporated under reduced pressure to give 42.1 g
of a dark green oil. Crystallization from ethanol furnished 33.5
g of di-2-indenecarboxylate 15a (97% based on 8a ) as slightly
green crystals. Mp: 129 °C. [R]20D: -133.9° (c ) 0.90, CHCl3).
a 2: A 62:38 mixture of diastereomeric diols 8a and 9a was
prepared by the procedure described above from 20.0 g of a
62:38 mixture of diesters 5a and 6a (68.4 mmol) and 3.11 g of
LiAlH4 (82.0 mmol). After workup, 15.9 g of a white solid mass
was obtained. Separation of the diastereomers was ac-
complished by column chromatography of three portions of 5.30
g on 400 g of silica gel with ethyl acetate. The less polar
fraction furnished 5.58 g of 9a (91% based on 6a ). Further
elution yielded 9.20 g of the main diastereomer 8a (92% based
on 5a ).
IR (KBr): 3019, 2948, 2823, 1703, 1567 cm-1
m/z 489 (M - MeO)+. 1H-NMR (CDCl3, 300 MHz): δ 1.34 (s,
. MS (70 eV):
2
4
6), 3.33 (s, 6), 3.50, 3.58 (2 dd, 4, | J | ) 13.8 Hz, J ) 2.0 Hz),
8a . Mp: 120 °C. [R]20D: -165.1° (c ) 1.21, CHCl3). IR
(KBr): 3449, 3403, 2961, 2837, 1428, 857 cm-1. MS (70 eV):
m/z 205 (M - MeO)+. 1H-NMR (CDCl3, 300 MHz): δ 2.95 (“t”,
2
3
4.10 (m, 2), 4.38, 4.43 (2 “dd”, 4, | J | ) 12.1 Hz, J ) 4.0, 4.7
Hz), 7.27-7.48 (m, 8), 7.62 (t, 2). 13C-NMR (75 MHz, CDCl3):
δ 17.49, 38.13, 48.02, 63.77, 67.96, 98.97, 123.49, 124.24,
126.86, 127.69, 136.52, 141.72, 142.50, 144.76, 164.40. Anal.
Calcd for C30H32O8: C, 69.22; H, 6.20. Found: C, 69.11; H,
6.20.
3
2, J ) 6 Hz, OH), 3.69 (m, 4), 3.79 (m, 2). Remaining NMR
data in accordance with ref 8. Anal. Calcd for C10H20O6: C,
50.84; H, 8.53. Found: C, 51.02; H, 8.48.
(2S,3S,5S,6S)-2,3-Bis(h yd r oxym et h yl)-5,6-d im et h oxy-
5,6-d im eth yl[1,4]d ioxa n e (9a ). Mp: 74 °C. [R]20D: +100.4°
(c ) 1.01, CHCl3). IR (KBr): 3471, 3306, 2951, 2836, 1309,
852 cm-1. MS (70 eV): m/z 236 (M)+. 1H-NMR (CDCl3, 300
MHz): δ 1.40 (s, 6), 2.94 (br s, 2), 3.34 (s, 6), 3.69 (m, 4), 4.03
(m, 2). 13C-NMR (75 MHz, CDCl3): δ 17.60, 48.49, 63.13,
73.34, 100.51. Anal. Calcd for C10H20O6: C, 50.84; H, 8.53.
Found: C, 50.83; H, 8.50.
Gen er a l P r oced u r e for Ir r a d ia tion of 10a -d , 15a , a n d
15b. All temperature-dependent measurements were carried
out under nitrogen in a photoreactor which was fitted with
an immersion well (vacuum jacket, Pyrex glass) and a high
pressure mercury lamp HPK 125 W (Philips). The photore-
actor was plunged in a thermostated bath and charged with a
solution of 2.00 g of the respective compounds 10 and 15 in
200 mL of toluene. After 30 min of thermostatization, the
solution was irradiated for 60 h in the case of 10 and 36 h in
the case of 15, respectively. Then, the solvent was evaporated
and the ratio of the isomeric products was determined by 13C-
NMR spectra of the obtained slightly yellow solid residues.
Separation and purification of the diasteromeric and regio-
isomeric products were accomplished by column chromatog-
raphy and crystallization. Assignments were verified by NOE
and COSY experiments, as well as by conversion of the
diastereomeric truxinates into the corresponding dimethyl
truxinates by treatment with SOCl2 in boiling methanol.7,12
Ir r a d ia tion of 10a . The residue obtained upon irradiation
of 2.00 g of 10a at -28 °C was chromatographed on 220 g of
silica gel with 4:1 hexane-ethyl acetate to give in order of
increasing polarity 12a (colorless needles upon recrystalliza-
tion from ethyl acetate-hexane), 13a (foamy colorless solid),
11a (colorless hexagonal prisms upon recrystallization from
ether), and 14a (colorless wax) along with fractions containing
mixtures of diastereomers. The total amount of truxinates was
1.78 g (89% based on 10a ).
(2R,3R,5S,6S)-2,3-Diet h oxy-5,6-b is(h yd r oxym et h yl)-
2,3-d im eth yl[1,4]d ioxa n e (8b). This compound was pre-
pared in analogy to the procedure for 8a from 174 g of diester
5b (0.50 mol, de ) 92%) and 22.8 g of LiAlH4 (0.60 mol). The
solid white residue (130 g) obtained after workup was recrys-
tallized from ether-pentane to afford 116 g of 8b (88% based
on 5b) as colorless needles. The mother liquor was concen-
trated in vacuum to give 9.8 g of a yellow oil containing a 59:
41 mixture of diastereomers 9b and 8b. This residue was
subjected to column chromatography on 500 g of silica gel with
ethyl acetate to give 4.73 g of diol 9b as a colorless solid
followed by 3.16 g of diol 8b. Mp: 121 °C. [R]20D: -136.2° (c
) 1.00, CHCl3). IR (KBr): 3544, 3411, 2991, 2894, 1441, 854
cm-1
.
MS (70 eV): m/z 219 (M - EtO)+. 1H-NMR (CDCl3,
2
300 MHz): δ 3.51, 3.54 (2 dq, 4, | J | ) 9.4 Hz), 3.64, 3.70 (2
“dd”, 4, | J | ) 12.1 Hz, 3J ) 4.5, 3.5 Hz). Remaining NMR
2
data in accordance with ref 8. Anal. Calcd for C12H24O6: C,
54.53; H, 9.15. Found: C, 54.75; H, 9.36.
(2S,3S,5S,6S)-2,3-Dieth oxy-5,6-bis(h yd r oxym eth yl)-2,3-
d im eth yl[1,4]d ioxa n e (9b). Mp: 64 °C. [R]20D: +68.1° (c
) 1.00, CHCl3). IR (KBr): 3394, 2977, 2877, 757 cm-1. MS
(70 eV): m/z 174 (M - 2 EtO)+. 1H-NMR (CDCl3, 300 MHz):
(-)-δ-Tr u xin a te 12a . Mp: 220 °C. [R]20D: -74.1° (c )
1.02, CHCl3). IR (KBr): 3028, 2954, 2829, 1738, 1605, 1429,
886 cm-1. MS (70 eV): m/z 465 (M - MeO)+. 1H-NMR (CDCl3,
300 MHz): δ 1.29 (s, 6), 3.08 (half of AA′BB′ pattern, 2), 3.26
(s, 6), 3.88 (half of AA′BB′ pattern, 2), 3.90 (m, 2), 3.97 (dd, 2,
3
δ 1.19 (t, 6, J ) 7.1 Hz), 1.41 (s, 6), 2.71 (br s, 2), 3.56, 3.72
2
(2 dq, 4, | J | ) 9.1 Hz), 3.67 (m, 4), 4.12 (m, 2). 13C-NMR (75
MHz, CDCl3): δ 15.79, 18.67, 56.36, 63.31, 73.07, 100.41.
Anal. Calcd for C12H24O6: C, 54.53; H, 9.15. Found: C, 54.58;
H, 9.14.
2
| J | ) 11.1 Hz, 3J ) 2.0 Hz), 4.37 (“dd”, 2, 3J ) 10.1 Hz), 7.19-
7.33 (m, 10). 13C-NMR (75 MHz, CDCl3): δ 17.27, 44.42, 48.20,
49.92, 66.11, 69.91, 98.85, 126.78, 127.25, 128.67, 139.84,
170.94. Anal. Calcd for C28H32O8: C, 67.73; H, 6.50. Found:
C, 68.06; H, 6.51.
(2S,3S,5R,6R)-2,3-Bis(((E)-cin n a m oyloxy)m et h yl)-5,6-
d im eth oxy-5,6-d im eth yl[1,4]d ioxa n e (10a ). To a solution
of 77.7 g of cinnamoyl chloride (0.466 mol) and 1.0 g of DMAP
(8.2 mmol) in 150 mL of CH2Cl2 was dropped 50.0 g of diol 8a
(0.212 mol) in 300 mL of 1:1 pyridine-CH2Cl2 at a rate
maintaining the temperature below 30 °C. After stirring the
reaction mixture for 20 h at room temperature, 500 mL of CH2-
Cl2 and 600 mL of 2 M H2SO4 were added. The phases were
separated, and the aqueous layer was extracted twice with 250
mL of CH2Cl2. The combined organic phase was washed with
200 mL of saturated NaHCO3, dried, filtered, and concentrated
under vacuum to give 118 g of a yellow oil. Crystallization
from ethanol afforded 101 g of dicinnamate 10a (96% based
on 8a ) as colorless crystals. Mp: 138 °C. [R]20D: -127.4° (c
â-Tr u xin a te 13a . Mp: 76 °C. [R]20D: -74.2° (c ) 0.95,
CHCl3). IR (KBr): 3029, 2957, 2834, 1741, 1605, 1249 cm-1
.
MS (70 eV): m/z 465 (M - MeO)+. 1H-NMR (CDCl3, 300
3
MHz): δ 1.30 (s, 6), 3.30 (s, 6), 3.80 (dd, 1, J ) 10.2, 5.5 Hz),
3
2
3.94 (dd, 1, J ) 6.4 Hz), 3.99, 4.03 (2 m, 2), 4.14 (dd, 1, | J | )
11.8 Hz, 3J ) 3.4 Hz), 4.27 (dd, 1, | J | ) 11.8 Hz, 3J ) 4.0 Hz),
2
3
3
4.45 (m, 2, PhCH), 4.55 (dd, 1, J ) 7.9 Hz), 4.71 (dd, 1, J )
9.1 Hz), 6.90 (m, 2), 6.93 (m, 2), 7.01-7.14 (m, 6). 13C-NMR
(75 MHz, CDCl3): δ 17.36 (2 C), 44.24, 44.60, 44.69, 44.73,
48.38 (2 C), 64.43, 64.70, 67.98, 68.55, 98.38 (2 C), 126.51,
126.55, 127.61, 127.79, 128.08, 128.12, 137.89, 137.95, 170.86,
171.28. Anal. Calcd for C28H32O8: C, 67.73; H, 6.50. Found:
C, 68.09; H, 6.71.
) 1.07, CHCl3). IR (KBr): 3025, 2945, 2825, 1718, 1639 cm-1
.
MS (70 eV): m/z 465 (M - MeO)+. 1H-NMR (CDCl3, 300
MHz): δ 1.34 (s, 6), 3.31 (s, 6), 4.06 (m, 2), 4.30, 4.41 (2 “dd”,
2
3
3
4, | J | ) 12.1 Hz, J ) 4.0, 4.7 Hz), 6.44 (d, 2, J ) 16.1 Hz),
(24) Treibs, W.; Orttmann, H. Chem. Ber. 1960, 93, 545.

6134 J . Org. Chem., Vol. 61, No. 18, 1996
Haag and Scharf
(+)-δ-Tr u xin a te 11a . Mp: 174 °C. [R]20D: +12.2° (c )
redissolved in ether, and pentane was added until the solution
became turbid. On standing in the refrigerator, the product
crystallized to give 16.1 g of 11a (67% based on 10a ) as
colorless, hexagonal prisms.
1.00, CHCl3). IR (KBr): 3027, 2961, 2835, 1747, 1603, 1422,
1077 cm-1
.
MS (70 eV): m/z 465 (M - MeO)+. 1H-NMR
(CDCl3, 300 MHz): δ 1.31 (s, 6), 3.17 (half of AA′BB′ pattern,
2), 3.28 (s, 6), 3.86 (half of AA′BB′ pattern, 2), 3.99 (m, 2), 4.03
(1S,5S,7R,8R,10S,14S,15S,19S)-Diben zo-7,8-d im eth oxy-
7,8-d im e t h yl-2,13-d ioxo-3,6,9,12-t e t r a oxa p e n t a cyclo-
[12.4.4.05,10.01,15.014,19]d ocosa -16,20-d ien e (16a ). Ten por-
tions of 3.34 g of di-2-indenecarboxylate 15a (64.2 mmol) were
irradiated respectively in 220 mL of toluene for 36 h at -70
°C. On concentrating the combined toluene solutions to 300
mL, product 16a precipitated. The crystals were filtered off
and washed with ether to give 15.4 g of 16a as a colorless
powder. A second crop of 0.6 g of 16a was obtained from the
mother liquor upon crystallization from CH2Cl2-pentane (total
yield of 16.0 g, 48% based on 15a ).
(1R,2R,3S,4S)-1,2-Bis(h yd r oxym eth yl)-3,4-d ip h en ylcy-
clobu ta n e (19). To a stirred suspension of 1.13 g of LiAlH4
(29.8 mmol) in 100 mL of dry THF was added 9.85 g of diester
11a (19.8 mmol) in portions at a rate maintaining gentle
reflux. The reaction mixture was allowed to cool to ambient
temperature and stirred for 3 h. Hydrolysis of the excess
LiAlH4 was accomplished by careful addition of 10% KOH (∼5
mL) just to the point that the gray slurry turned white. Then,
the reaction mixture was heated at reflux for another hour.
After filtration the white precipitate was extracted twice with
50 mL of boiling 95:5 THF-water. The combined THF
solution was dried, filtered, and evaporated to give 10.34 g of
a solid white residue. This residue was suspended in 150 mL
boiling ether, concentrated to 60 mL, and filtered off to give
4.47 g of diol 19. A second crop of 0.75 g of 19 (total yield of
5.32 g, 98% based on 11a ) was obtained from the mother liquor
by complete removal of ether and subsequent crystallization
from 8 mL of ethanol. The filtrate was concentrated under
2
3
(m, 2), 4.61 (dd, 2, | J | ) 12.1 Hz, J ) 2.4 Hz), 7.19-7.34 (m,
10). 13C-NMR (75 MHz, CDCl3): δ 17.36, 44.52, 48.13, 50.20,
65.28, 67.62, 99.45, 126.76, 127.27, 128.67, 139.73, 171.53.
Anal. Calcd for C28H32O8: C, 67.73; H, 6.50. Found: C, 67.48;
H, 6.57.
Neotr u xin a te 14a . [R]20D: -13.7° (c ) 1.41, CHCl3). IR
(CHCl3): 3029, 2953, 2834, 1750, 1605, 1413 cm-1
. MS (70
eV): m/z 465 (M - MeO)+. 1H-NMR (CDCl3, 300 MHz): δ 1.29,
3
1.33 (2 s, 6), 3.24, 3.29 (2 s, 6), 3.56 (dd, 1, J ) 11.8, 8.1 Hz),
3.83 (“dd”, 1, | J | ) 11.6 Hz, 3J ) 5.9 Hz), 4.03-4.11 (m, 3),
2
3
3
4.12 (t, 1, J ) 11.8 Hz), 4.13 (t, 1, J ) 8.2 Hz), 4.33 (dd, 1),
2
3
4.53 (dd, 1, | J | ) 11.8 Hz, J ) 3.0 Hz), 4.65 (m, 1), 6.87 (m,
2), 7.02-7.19 (m, 8). 13C-NMR (75 MHz, CDCl3): δ 17.41 (2
C), 42.16, 45.53, 45.74, 48.14, 48.24, 49.22, 64.22, 65.36, 67.37,
68.04, 99.44, 99.60, 126.31, 126.74, 127.65, 128.12, 130.13,
134.81, 137.41, 169.33, 172.55. Anal. Calcd for C28H32O8: C,
67.73; H, 6.50. Found: C, 67.97; H, 6.67.
Ir r a d ia tion of 15a . The residue obtained upon irradiation
of 2.00 g of 15a at -40 °C was suspended in 10 mL of CH2Cl2
and filtered off to yield pure 16a as a white powder (suitable
crystals for X-ray analysis upon recrystallization from CH2-
Cl2). The filtrate was concentrated and chromatographed on
220 g of silica gel with 4:1 hexane-ethyl acetate to give in
order of increasing polarity 18a (colorless needles upon re-
crystallization from ether), 17a (foamy colorless solid), and 16a
along with fractions containing mixtures of isomers. The total
amount of indene-2-carboxylate dimers was 1.92 g (96% based
on 15a ).
syn -H ea d -t o-H ea d In d en e-2-ca r b oxyla t e Dim er 18a .
reduced pressure, and the residue was redissolved in a
minimum of ether. On standing in the refrigerator, diol 8a
Mp: 233 °C. [R]20D: -37.0° (c ) 1.06, CHCl3). IR (KBr): 3012,
2956, 2832, 1745, 1207 cm-1
.
MS (70 eV): m/z 489 (M -
precipitated to give 4.50 g of colorless crystals (95% based on
MeO)+. 1H-NMR (CDCl3, 300 MHz): δ 1.30 (s, 6), 3.23 (d, 1,
11a ). Mp: 122 °C. [R]20
: -83.4° (c ) 1.06, CHCl3). IR
D
2
2
| J | ) 18.0 Hz), 3.28 (d, 1, | J | ) 17.5 Hz), 3.30, 3.32 (2 s, 6),
(KBr): 3343, 3279, 3026, 2926, 2864, 1602 cm-1. MS (70 eV):
m/z 268 (M)+, 134 (M/2)+. 1H-NMR (CDCl3, 300 MHz): δ 2.37
(m, 2), 3.12 (br s, 2), 3.16 (half of AA′BB′ pattern, 2), 3.60 (“t”,
3.33 (d, 1), 3.43 (d, 1), 4.00, 4.08 (2 td, 2, 3J ) 9.4, 4.0 Hz),
2
3
4.12, 4.16 (2 dd, 2, | J | ) 11.4 Hz, J ) 4.0 Hz), 4.56, 4.60 (2
3
2
3
2
d, 2, J ) 9.1 Hz), 4.65, 4.70 (2 dd, 2), 6.82-6.99 (m, 8). 13C-
2, | J | ∼ J ) 9.7 Hz), 3.92 (dd, 2, | J | ) 10.2 Hz, 3J ) 3.5 Hz),
7.17-7.33 (m, 10). 13C-NMR (75 MHz, CDCl3): δ 47.29, 47.52,
65.32, 126.60, 126.80, 128.54, 142.35. Anal. Calcd for
C18H20O2: C, 80.56; H, 7.51. Found: C, 80.29; H, 7.51.
(1S,2S,6S,7S)-Diben zo-1,6-bis(h yd r oxym eth yl)tr icyclo-
[5.3.0.02,6]d eca -3,8-d ien e (24). This compound was prepared
in analogy to the procedure for 19 from 1.18 g of LiAlH4 (31.1
mmol) and 10.8 g of diester 16a (20.7 mmol) in 125 mL of THF.
The crude product (11.4 g) was purified by column chroma-
tography on 220 g silica gel with 6:1 ethyl acetate-hexane to
furnish 5.81 g of diol 24 (96% based on 16a ) as a white solid.
Further elution with pure ethyl acetate gave 4.73 g of diol 8a
(97% based on 16a ). Mp: 138 °C. [R]20D: -247.5° (c ) 1.12,
CHCl3). IR (KBr): 3221, 3018, 2922, 2832 cm-1. MS (70 eV):
m/z 292 (M)+, 146 (M/2)+. 1H-NMR (CDCl3, 300 MHz): δ 2.53,
NMR (75 MHz, CDCl3): δ 17.39 (2 C), 37.18, 37.64, 48.50,
48.56, 51.89, 51.96, 56.07, 56.59, 64.19, 64.37, 67.64, 67.70,
97.71 (2 C), 124.01, 124.08, 125.37, 125.72, 126.36, 126.41,
126.92, 140.23, 140.46, 142.86, 143.27, 173.83, 174.06. Anal.
Calcd for C30H32O8: C, 69.22; H, 6.20. Found: C, 69.13; H,
6.17.
a n ti-Hea d -to-Hea d In d en e-2-ca r boxyla te Dim er 17a .
Mp: 235 °C. [R]20D: -40.2° (c ) 1.03, CHCl3). IR (KBr): 3022,
2956, 2833, 1747, 1736, 1198, 1013 cm-1
. MS (70 eV): m/z
489 (M - MeO)+. 1H-NMR (CDCl3, 300 MHz): δ 1.34 (s, 6),
2
3.32 (s, 6), 3.70 (d, 2, | J | ) 18.0 Hz), 3.78 (s, 2), 3.82 (d, 2),
4.04 (m, 2), 4.06 (m, 2), 4.64 (m, 2), 7.09-7.28 (m, 8). 13C-
NMR (75 MHz, CDCl3): δ 17.44, 38.05, 48.16, 53.25, 60.44,
65.25, 67.97, 99.24, 122.95, 124.62, 126.84, 127.30, 143.05,
143.16, 170.56. Anal. Calcd for C30H32O8: C, 69.22; H, 6.20.
Found: C, 69.04; H, 6.25.
2
2.66 (2 d, 4, | J | ) 17.3 Hz), 3.88 (s, 4), 3.92 (br s, 2), 3.94 (s,
2), 6.82 (m, 2), 6.97 (m, 2), 7.06 (m, 2), 7.09 (m, 2). 13C-NMR
(75 MHz, CDCl3): δ 37.92, 50.07, 50.68, 69.06, 124.55, 125.98,
126.03, 126.62, 142.43, 144.79. Anal. Calcd for C20H20O2: C,
82.16; H, 6.90. Found: C, 82.03; H, 7.12.
syn -H ea d -t o-Ta il In d en e-2-ca r b oxyla t e Dim er 16a .
Mp: >270 °C. [R]20D: -228.0° (c ) 0.84, CHCl3). IR (KBr):
3020, 2961, 2832, 1719, 1441, 1437, 1346 cm-1. MS (70 eV):
m/z 489 (M - MeO)+. 1H-NMR (CDCl3, 300 MHz): δ 1.33 (s,
(1S,2S,3R,4R)-1,2-Dip h en yl-3,4-bis(((t olyl-4-su lfon yl)-
oxy)m eth yl)cyclobu ta n e (20). To a solution of 11.8 g of
tosyl chloride (62.0 mmol) and 0.49 g of DMAP (4.0 mmol) in
60 mL of 25:10 CH2Cl2-pyridine was added 45 mL of a
solution of 5.55 g of diol 19 (20.7 mmol) in 25:10 CH2Cl2-
pyridine. The reaction mixture was stirred at ambient tem-
perature for ∼12 h until TLC (1:1 hexane-ethyl acetate)
indicated nearly complete conversion and new less polar
compound appeared. To hydrolyze the excess tosyl chloride,
10 mL of water was added and the mixture was stirred for
two more hours. After neutralization with 2 M H2SO4, the
phases were separated, and the aqueous layer was extracted
twice with 100 mL of CH2Cl2. The combined organic phase
was washed with 50 mL of saturated NaHCO3, dried, filtered,
and concentrated under vacuum to give 12.9 g of a yellow oil.
Crystallization from methanol afforded 10.73 g of ditosylate
2
6), 3.11, 3.25 (2 d, 4, | J | ) 17.0 Hz), 3.33 (s, 6), 4.12 (m, 2),
2
3
4.38 (“dd”, 2, | J | ) 11.8 Hz, J ) 7.1 Hz), 4.48 (s, 2), 4.55 (dd,
3
2, J ) 2.8 Hz), 6.73 (m, 2), 6.93 (m, 2), 7.06 (m, 2), 7.11 (m,
2). 13C-NMR (75 MHz, CDCl3): δ 17.40, 37.20, 48.28, 54.89,
55.32, 65.58, 68.86, 98.97, 124.15, 125.37, 126.12, 127.45,
138.44, 143.35, 175.70. Anal. Calcd for C30H32O8: C, 69.22;
H, 6.20. Found: C, 69.33; H, 6.33.
(1R,5S,7R,8R,10S,14R,15S,16S)-7,8-Dim et h oxy-7,8-d i-
m eth yl-2,13-dioxo-15,16-diph en yl-3,6,9,12-tetr aoxatr icyclo-
[12.2.0.05,10]h exa d eca n e (11a ). Eight portions of 3.00 g of
dicinnamate 10a (48.3 mmol) were irradiated respectively in
200 mL of toluene for 60 h at -60 °C. Then, the combined
toluene solutions were concentrated in vacuum to give 25.6 g
of a solid yellow residue, which was roughly purified by column
chromatography on 450 g of silica gel with 4:1 hexane-ethyl
acetate. The obtained slightly yellow solid (18.5 g) was
20 (90% based on 19) as colorless crystals. Mp: 121 °C. [R]20
:
D

Asymmetric Intramolecular [2 + 2] Photocycloaddition
-32.3° (c ) 1.04, CHCl3). IR (KBr): 3028, 2924, 1598, 1369,
J . Org. Chem., Vol. 61, No. 18, 1996 6135
based on 25) as a colorless, nearly insoluble powder. Mp: 273
°C. [R]20D: -34.9° (c ) 0.045, CHCl3). IR (KBr): 3052, 2878,
1174 cm-1
.
MS (70 eV): m/z 288 (M/2)+. 1H-NMR (CDCl3,
300 MHz): δ 2.44 (s, 6), 2.50 (m, 2), 3.25 (half of AA′BB′
2411, 2389, 2354, 1436 cm-1
.
1H-NMR (CDCl3, 300 MHz): δ
2
2
pattern, 2), 4.09 (“dd”, 2, | J | ) 10.6 Hz, 3J ) 4.0 Hz), 4.13
0.6-1.6 (br s, 6), 2.35, 2.77 (2 d, 4, | J | ) 17.0 Hz), 2.94 (dd, 2,
3
2
2
2
(“dd”, 2, J ) 3.7 Hz), 7.06 (m, 4), 7.16-7.28 (m, 6), 7.33 (m,
| J |P,H ) 12.6 Hz, | J | ) 14.6 Hz), 3.23 (dd, 2, | J |P,H ) 10.2
Hz), 3.83 (s, 2), 6.48 (m, 2), 6.81 (m, 2), 6.99 (m, 2), 7.32 (m,
2), 7.40-7.54 (m, 12), 7.72-7.80 (m, 8). Anal. Calcd for
C44H44P2B2: C, 80.51; H, 6.76. Found: C, 80.23; H, 6.70.
(1R,2R,3S,4S)-1,2-Bis((d ip h en ylp h osp h a n yl)m et h yl)-
3,4-d ip h en ylcyclobu ta n e (22). The whole procedure, work-
up included, was conducted under an Ar atmosphere. To a
solution of 1.40 g of 21 (2.21 mmol) in 20 mL of CH2Cl2 at
room temperature was added 1.90 mL of HBF4‚OMe2 (22.2
mmol) with a stainless steel cannula. Then, the mixture was
heated at reflux for 6 h, while the liberated diborane was
removed by an Ar stream at the top of the reflux condenser.
After cooling to ambient temperature and careful neutraliza-
tion with saturated, degassed NaHCO3, the organic layer was
taken with a syringe fitted with a stainless steel cannula. The
aqueous layer was extracted twice with 20 mL of CH2Cl2. The
combined organic phase was dried, filtered, and concentrated
in vacuum to furnish 1.30 g of diphosphane 22 (97% based on
27) as a colorless, foamy solid. Mp: 61 °C. [R]20D: -17.4° (c
) 0.77, CHCl3). IR (KBr): 3052, 3026, 2919, 1600, 1584, 1433
cm-1. MS (70 eV): m/z 604 (M)+, 302 (M/2)+. 1H-NMR (CDCl3,
300 MHz): δ 2.34 (m, 4), 2.48 (m, 2), 2.99 (half of AA′BB′
pattern, 2), 2.79 (m, 2), 7.02 (m, 4), 7.10-7.34 (m, 26). 13C-
4), 7.76 (m, 4). 13C-NMR (75 MHz, CDCl3): δ 21.65, 40.77,
46.12, 70.19, 126.86, 126.90, 127.90, 128.58, 129.99, 132.88,
141.01, 145.00. Anal. Calcd for C32H32O6S2: C, 66.64; H, 5.59.
Found: C, 66.42; H, 5.59.
(1S,2S,6S,7S)-Dib en zo-1,6-b is(((t olyl-4-su lfon yl)oxy)-
m eth yl)tr icyclo[5.3.0.02,6]d eca -3,8-d ien e (25). This com-
pound was prepared in analogy to the procedure for 20 from
11.3 g of tosyl chloride (59.4 mmol), 0.49 g of DMAP (4.0 mmol),
and 5.78 g of diol 24 (19.8 mmol) in 105 mL of 25:10 CH2Cl2-
pyridine. Purification of the crude product (12.7 g) was
accomplished by column chromatography on 220 g of silica gel.
After removal of less polar impurities with 6:1 hexane-ethyl
acetate, elution with 3:2 hexane-ethyl acetate furnished 11.0
g of ditosylate 25 (93% based on 24) as a colorless solid. Mp:
65 °C. [R]20D: -92.2° (c ) 0.95, CHCl3). IR (KBr): 3022, 2923,
2844, 1598, 1361, 1177 cm-1
. MS (70 eV): m/z 428 (M -
TsOH)+, 300 (M/2)+. 1H-NMR (CDCl3, 300 MHz): δ 2.45 (s,
2
6), 2.56, 2.66 (2 d, 4, | J | ) 17.3 Hz), 3.58 (s, 2), 4.16, 4.32 (2
2
d, 4, | J | ) 9.7 Hz), 6.76 (m, 2), 6.97 (m, 2), 6.99 (m, 2), 7.09
(m, 2), 7.38 (m, 2), 7.86 (m, 2). 13C-NMR (75 MHz, CDCl3): δ
21.67, 37.73, 47.82, 51.86, 75.33, 124.49, 125.90, 126.36,
127.20, 128.00, 130.07, 132.75, 140.40, 143.88, 145.07. Anal.
Calcd for C34H32O6S2: C, 67.98; H, 5.37. Found: C, 67.66; H,
5.18.
1
NMR (75 MHz, CDCl3): δ 34.50 (d, | J |P,C ) 12.2 Hz), 44.21
2
3
3
(t, | J |P,C ) | J |P,C ) 10.4 Hz), 53.37 (d, | J |P,C ) 9.2 Hz), 126.16,
2
127.30, 128.14, 128.26, 128.35, 128.55, 132.55 (d, | J |P,C ) 18.3
(1R,2R,3S,4S)-1,2-Bis((bor a n a tod ip h en ylp h osp h a n yl)-
m eth yl)-3,4-d ip h en ylcyclobu ta n e (21). The reaction was
conducted under an Ar atmosphere in a flame-dried Schlenk
flask fitted with a rubber septum. To a solution of 1.00 g of
diphenylphosphane-borane25 (4.99 mmol) in 3.0 mL of THF
at 0 °C was added 3.12 mL of 1.6 M n-butyllithium (4.99 mmol)
in hexane. The resulting slightly turbid solution was stirred
at 0 °C for 1 h, cooled to -50 °C, and treated with a solution
prepared from 1.20 g of ditosylate 20 (2.08 mmol) and 4.0 mL
of DMF in a seperate Schlenk flask under an Ar atmosphere.
The mixture was allowed to warm to ambient temperature
over 3 h and stirred for additional 16 h. Then, the reaction
mixture was poured on 20 mL of saturated NH4Cl, and the
aqueous layer was extracted four times with 25 mL of toluene.
The combined organic phase was dried, filtered, and evapo-
rated in vacuum to give 1.4 g of a white solid. The crude
product was recrystallized from ethanol to furnish 1.05 g of
2
1
Hz), 133.06 (d, | J |P,C ) 19.5 Hz), 138.35 (d, | J |P,C ) 13.5 Hz),
138.85 (d, | J |P,C ) 12.8 Hz), 142.52. 31P-NMR (203 MHz,
1
CDCl3): δ -23.93. Anal. Calcd for C42H38P2: C, 83.42; H,
6.33. Found: C 83.06, ; H, 6.24.
(1S,2S,6S,7S)-Dib en zo-1,6-b is((d ip h en ylp h osp h a n yl)-
m eth yl)tr icyclo[5.3.0.02,6]d eca -3,8-d ien e (27). This com-
pound was prepared in analogy to the procedure for 22 from
2.80 g of 26 (4.27 mmol) in 50 mL of CH2Cl2 and 5.20 mL of
HBF4‚OMe2 (42.7 mmol). The described workup procedure
yielded 2.63 g of 27 as a colorless, foamy solid. On recrystal-
lization from ethanol 2.48 g of diphosphane 27 (93% based on
26) was obtained as colorless crystals. Mp: 112 °C. [R]20
:
D
-72.6° (c ) 0.83, CHCl3). IR (KBr): 3069, 3018, 2905, 1584,
1434 cm-1. MS (70 eV): m/z 628 (M)+, 314 (M/2)+. 1H-NMR
2
(CDCl3, 300 MHz): δ 2.53, 2.65 (2 d, 4, | J | ) 17.5 Hz), 2.71
2
2
2
(dd, 2, | J |P,H ) 3.4 Hz, | J | ) 13.8 Hz), 2.91 (dd, 2, | J |P,H
)
2.7 Hz), 3.55 (s, 2), 6.65 (m, 2), 6.88 (m, 2), 7.01 (m, 2), 7.04
21 (80% based on 20) as colorless crystals. Mp: 156 °C. [R]20
:
D
(m, 2), 7.26-7.58 (m, 20). 13C-NMR (75 MHz, CDCl3): δ 41.13
+11.1° (c ) 1.13, CHCl3). IR (KBr): 3056, 3026, 2925, 2375,
3
1
(d, | J |P,C ) 9.8 Hz), 42.47 (d, | J |P,C ) 15.8 Hz), 48.01 (d,
2343, 1602, 1437 cm-1
.
1H-NMR (CDCl3, 500 MHz): δ 0.5-
2 2 3
2
3
3
| J |P,C ) | J |P,C ) 15.2 Hz), 60.38 (t, | J |P,C ) 9.5 Hz), 124.02,
1.3 (br s, 6), 2.43 (ddd, 2, | J | ) 15.0 Hz, | J |P,H ) 11.3 Hz, J
3
125.64, 125.75, 126.33, 128.41, 128.55 (d, | J |P,C ) 8.6 Hz),
) 4.9 Hz), 2.50 (ddd, 2, | J |P,H ) 13.0 Hz, 3J ) 6.6 Hz), 2.66
2
2
2
133.06 (d, | J |P,C ) 19.5 Hz), 133.19 (d, | J |P,C ) 20.1 Hz), 139.40
(half of AA′BB′ pattern, 2), 2.79 (m, 2), 6.76 (m, 4), 7.05-7.08
(m, 6), 7.21 (m, 4), 7.30-7.38 (m, 8), 7.44 (m, 4), 7.52 (m, 4).
1
1
(d, | J |P,C ) 12.8 Hz), 139.51 (d, | J |P,C ) 13.4 Hz), 142.53,
145.05. 31P-NMR (203 MHz, CDCl3): δ -23.33. Anal. Calcd
for C44H38P2: C, 84.06; H, 6.09. Found: C, 83.74; H, 6.12.
13C-NMR (75 MHz, CDCl3): δ 31.56 (d, | J |P,C ) 34.2 Hz), 40.53
1
2
3
(d, | J |P,C ) 9.2 Hz), 55.04 (d, | J |P,C ) 6.1 Hz), 126.22, 127.04,
3
3
128.09, 128.60 (d, | J |P,C ) 10.3 Hz), 128.88 (d, | J |P,C ) 9.8
Ack n ow led gm en t. Support of this work by a re-
search grant from the Deutsche Forschungsgemein-
schaft (Sonderforschungsbereich 380, Teilprojekt D) is
gratefully acknowledged. The NMR spectra were kindly
recorded by Dr. J an Runsink. We are also indebted to
laboratory assistant Susanne Ko¨rfer for her contribution
to the success of this project and to Christoph J ansen
for performing the semiempirical calculations.
1
4
Hz), 129.40, 130.07 (d, | J |P,C ) 55.5 Hz), 131.01 (d, | J |P,C
)
4
2
2.5 Hz), 131.07 (d, | J |P,C ) 2.4 Hz), 131.86 (d, | J |P,C ) 9.2
2
Hz), 132.10 (d, | J |P,C ) 9.1 Hz), 140.51. 31P-NMR (203 MHz,
CDCl3): δ +12.22. 11B-NMR (160 MHz, CDCl3): δ -39.65.
Anal. Calcd for C42H44P2B2: C, 79.77; H, 7.01. Found: C,
79.91; H, 7.21.
(1S ,2S ,6S ,7S )-D i b e n z o -1,6-b i s ((b o r a n a t o d i p h e n -
ylph osph an yl)m eth yl)tr icyclo[5.3.0.02,6]deca-3,8-dien e (26).
This compound was prepared in analogy to the procedure for
21 from 2.34 g of diphenylphosphane-borane (11.7 mmol) in
7.0 mL of THF, 7.32 mL of 1.6 M n-butyllithium (11.7 mmol)
in hexane, and 2.93 g of ditosylate 25 (4.88 mmol) in 9.0 mL
of DMF. The crude product (3.7 g) was suspended in 20 mL
of boiling ethanol and filtered off to give 3.18 g of 26 (99%
Su p p or tin g In for m a tion Ava ila ble: An experimental
section for compounds 10b-d , 11b-d , 12b-d , 13b-d , 14b,
14c, 15b, 16b, 17b, and 18b (8 pages). This material is
contained in libraries on microfiche, immediately follows this
article in the microfilm version of the journal, and can be
ordered from the ACS; see any current masthead page for
ordering information.
(25) Imamoto, T.; Oshiki, T.; Onozawa, T.; Kusumoto, T.; Sato, K.
J . Am. Chem. Soc. 1990, 112, 5244.
J O960556Y