Asymmetric cyclization reactions of N-benzoyl-α-dehydroarylalanine alkyl esters via photoinduced electron transfer from achiral and chiral amines

Article abstract of DOI:10.3987/COM-11-12193

Irradiation of the title compounds [(Z)-1] having (S)-(+)-sec-butyl, (-)- menthyl, and related chiral auxiliaries in methanol and 1,2-dichloroethane containing 2-(diethylamino)ethanol afforded chiral auxiliary-substituted (4S,5S)-, (4R,5R)-, (4R,5S)-, and

Full text of DOI:10.3987/COM-11-12193

HETEROCYCLES, Vol. 83, No. 6, 2011
1329
HETEROCYCLES, Vol. 83, No. 6, 2011, pp. 1329 - 1353. © The Japan Institute of Heterocyclic Chemistry
Received, 28th February, 2011, Accepted, 7th April, 2011, Published online, 20th April, 2011
DOI: 10.3987/COM-11-12193
ASYMMETRIC CYCLIZATION REACTIONS OF N-BENZOYL-!-
DEHYDROARYLALANINE ALKYL ESTERS VIA PHOTOINDUCED
ELECTRON TRANSFER FROM ACHIRAL AND CHIRAL AMINES
Yuji Sasaki, Haruo Watanabe, Tetsutaro Igarashi, and Tadamitsu Sakurai*
Department of Material and Life Chemistry, Faculty of Engineering, Kanagawa
University, Kanagawa-ku, Yokohama 221-8686, Japan
Abstract– Irradiation of the title compounds [(Z)-1] having (S)-(+)-sec-butyl, (–)-
menthyl, and related chiral auxiliaries in methanol and 1,2-dichloroethane
containing 2-(diethylamino)ethanol afforded chiral auxiliary-substituted (4S,5S)-,
(4R,5R)-, (4R,5S)-, and (4S,5R)-4,5-dihydrooxazole derivatives (2) along with
(E)-1. It was found that the photoinduced electron transfer-initiated cyclization
of (Z)-1 gives either of the two diastereomers for cis-2 and trans-2 in
diastereomeric excess whose value varies from 8 to 81% depending on the
property of solvent as well as on the steric bulkiness of chiral auxiliary. On the
other hand, the asymmetric photocyclization of chiral auxiliary-unsubstituted (Z)-
1 in 1,2-dichloroethane proceeded cleanly in the presence of the chiral amine, (S)-
(–)-1-methylpyrrolidine-2-methanol, to give (4R,5R)-2 and (4R,5S)-2 in
enantiomeric excess of 17–38% and 20–33%, respectively, depending on the
steric bulkiness of the aryl substituent. A mechanistic consideration of these
diastereoselective and enantioselective photocyclization reactions enabled us
to propose major factors controlling the extent of asymmetric photoinduction.
INTRODUCTION
Excited state chemistry for organic molecules has continued to contribute to the development of novel
synthetic methods that enable the construction of pharmaceutically useful hetero atom-containing ring
systems.1 While sophisticated organic photochemistry has also contributed to the enhancement of
enantio- and diastereoselectivities in many asymmetric reactions,2–5 there have been only a few enantio-
and diastereodifferentiating photochemical reactions of synthetic utilities, particularly in liquid phase.
Since many photoinduced electron transfer (PET) reactions have been found to produce useful
heterocyclic compounds with high efficiencies,6 we attempted to develop a new type of diastereoselective
cyclization of N-benzoyl-!-dehydronaphthylalaninamides carrying some chiral auxiliaries, proceeding
through PET. This attempt made it possible to find PET-initiated asymmetric cyclization reactions
eventually affording the corresponding 3,4-dihydrobenzo[f]quinolinone derivatives in high diastereomeric
excesses (de).7 In addition, detailed analysis of the effects of tertiary amine, solvent, chiral auxiliary,
and temperature on the magnitude of de demonstrated that diastereoselectivity in this photocyclization

1330
HETEROCYCLES, Vol. 83, No. 6, 2011
strongly depended on the steric and electronic factors of the chiral auxiliary introduced.
On the other hand, it was quite recently found that the PET reaction of N-benzoyl-!-dehydroarylalanine
alkyl ester derivatives selectively afforded substituted 4,5-dihydrooxazoles even in less polar solvents.8
Because these products possess two asymmetric carbons in a dihydrooxazole ring, it is possible
to develop a novel type of the PET-initiated asymmetric cyclization of N-acyl-!-dehydroarylalanine alkyl
esters by introducing a chiral auxiliary into the ester moiety. In addition, a mechanistic consideration of
the PET reaction of !-dehydroarylalanine alkyl esters strongly suggested that triethylamine (TEA) as an
electron donor exists in the vicinity of key reaction intermediates during their cyclization processes
eventually affording the dihydrooxazole derivatives. It is, thus, very likely that alkyl ester derivatives of
N-acyl-!-dehydroamino acids undergo enantioselective photocyclization reactions in the presence of
chiral amines.
Me
H Et
Me
RO
O
1b: R =
1d: R =
1a: R =
O
H
N
H
Ph
Bu
Me
Ph
i-Pr
1c: R =
1e: R =
Me
Me
Me
(Z)-1a–f
1f: R = Me
Bu-t
t-BuO
O
O
t-BuO
O
O
N
H
Ph
H
H2N
N
H
Me
N
Ph
OH
H
N
H
N
OH
H
OH
H
OH
H
(Z)-1g
S-PM
R-PM
S-MPM
(Z)-1h
S-PG
Chart 1
To expand our study on the PET-initiated asymmetric cyclization of N-acyl-!-
dehydronaphthylalaninamides, we synthesized chiral auxiliary-substituted (Z)-N-benzoyl-!-dehydro(1-
naphthyl)alanine alkyl esters [(Z)-1a–d, Chart 1] and investigated the effects of substituent, solvent,
tertiary amine, and temperature on the magnitude of de, hoping to shed much light on the mechanism of
asymmetric photoinduction. Since a comprehensive analysis of diastereoselective and enantioselective
photocyclization reactions may elucidate not only the major factors governing de but also the
mechanism of these asymmetric photoreactions, we explored further the asymmetric photoreactions of
chiral auxiliary-unsubstituted (Z)-N-benzoyl-!-dehydroarylalanine alkyl esters [(Z)-1e–h] in the presence
of (S)-(+)-2-phenylglycinol (S-PG), (S)-(+)-pyrrolidine-2-methanol (S-PM), (R)-(–)-pyrrolidine-2-
methanol (R-PM) or (S)-(–)-1-methylpyrrolidine-2-methanol (S-MPM) (Chart 1).
RESULTS AND DISCUSSION
Absolute configuration and composition analysis
After a nitrogen-saturated methanol solution of (Z)-1a (4.0"10–3 mol dm–3, 500 mL) containing TEA

HETEROCYCLES, Vol. 83, No. 6, 2011
1331
(0.10 mol dm–3) had been irradiated with Pyrex-filtered light (>280 nm) from a 400 W high-pressure Hg
lamp for 5 h at room temperature (conversion, !100%), the reaction mixture obtained was subjected
to preparative thin layer chromatography on silica gel. This chromatography enabled us to isolate cis-
and
trans-4-[(S)-sec-butoxycarbonyl]-5-(1-naphthyl)-2-phenyl-4,5-dihydrooxazoles
as
their
diastereomeric mixtures [cis-2a: (4R,5R)-2a + (4S,5S)-2a, 78%; trans-2a: (4S,5R)-2a + (4R,5S)-2a, 8%
yield] having the vicinal coupling constants (J4,5) of 10.3 Hz and 6.3 Hz in DMSO-d6, respectively, as
shown in Scheme 1. The (E)-isomer of 1a was isolated independently from the reaction mixture, which
had been irradiated for 0.5 h under the same conditions (conversion, 20%), by similar workup (Scheme 1).
In addition, we were able to separate and isolate four diastereomers derived from cis-2a and trans-2a by a
combination of preparative thin layer, reversed phase, and normal phase chromatographic techniques.
However, any attempts were not fruitful to grow single crystals of these diastereomers. On the other
hand, in addition to the previous finding that TEA serves as an electron transfer catalyst for the PET-
initiated cyclization reaction of N-acetyl-!-dehydronaphthylalaninamides,6c negligible formation of
the TEA-derived byproducts substantiates the catalytic function of this amine in the above reaction.
Ph
Ph
N
N
h!
H
H
+
(Z)-1a
+
+
O
O
O
Et
O
Et
MeOH/TEA
H
H
1-Np O H Me
1-Np O H Me
1-Np = 1-naphthyl
(4R,5R)-2a
(4S,5S)-2a
Ph
Ph
N
H
N
H
+
(E)-1a
O
O
O
Et
O
Et
H
H
1-Np O H Me
1-Np O H Me
(4S,5R)-2a
(4R,5S)-2a
Scheme 1
To determine the absolute configuration of four diastereomers isolated, a nitrogen-saturated 1,2-
dichloroethane solution of (Z)-1e (4.0"10–3 mol dm–3, 500 mL) containing TEA (0.10 mol dm–3) was
irradiated under the same conditions as above for 5 h at room temperature (conversion, !100%). The
reaction mixture obtained was subjected to preparative thin layer chromatography on silica gel, which
afforded cis-2e and trans-2e in 56% and 28% yields, respectively. The former cis-isomer isolated as an
enantiomeric mixture was separated into (4S,5S)-2e and (4R,5R)-2e (showing intense circular
dichroism (CD) bands, the signs of which were reversed at 220 nm) by using a HPLC chiral column.
Because the observed CD bands are attributable to those of the naphthalene ring and, hence, their sign at
220 nm reflects the absolute configuration of each enantiomer at 5-position on the dihydrooxazole ring, it
is possible to unambiguously determine the configuration of a given diastereomer at this position from the
sign of its CD band at 220 nm. A single crystal showing the CD band of positive sign ([!]220 = +1390
deg cm2 dmol–1) was successfully grown and its structure was analyzed. The ORTEP drawing depicted
in Figure 1 established that (4S,5S)-2a,e and (4R,5S)-2a,e exhibit CD bands of positive sign and those of
negative sign are attributed to (4R,5R)-2a,e and (4S,5R)-2a,e. On the basis of these configurational

1332
HETEROCYCLES, Vol. 83, No. 6, 2011
assignments and diastereomeric composition ratios for cis-2a (1H NMR spectral analysis) and trans-2a
(1H NMR spectral and/or HPLC analysis), we were able to show that the PET-initiated cyclization of (Z)-
1a affords (4R,5R)-2a (de = 10%) and (4S,5R)-2a (de = 13%) in excess under given
conditions. To examine whether the amine-catalyzed isomerization of these two diastereomers takes
place, their methanol solutions containing TEA (0.10 mol dm–3) were allowed to stand for 3–4 h at
room temperature. 1H NMR spectral analysis revealed only a very little progress of the isomerization
(<5%). The de values for cis-2b–d and trans-2b–d were estimated according to the same spectroscopic
and chromatographic techniques as above.
Figure 1. ORTEP drawing of (4S,5S)-2e
Ph
Ph
N
N
h!
H
O
H
O
+
(Z)-1e
+
O
O
OBu-t
OBu-t
ClCH2CH2Cl/
S-MPM
H
H
1-Np
1-Np
(4R,5R)-2e
(4S,5S)-2e
1-Np = 1-naphthyl
Ph
Ph
N
H
N
H
+
O
O
OBu-t
OBu-t
H
1-Np
H
O
1-Np
O
(4S,5R)-2e
(4R,5S)-2e
Scheme 2
On the other hand, nitrogen-saturated 1,2-dichloroethane solutions of (Z)-1e (4.0"10–3 mol dm–3, 10 mL)
containing S-MPM (0.10 mol dm–3) were irradiated in parallel for 6 h at room temperature and the
resulting solutions were subjected to normal phase HPLC analysis after the chiral amine had been
removed by treatment with hydrochloric acid. For the purpose of determining the retention times of
HPLC signals and enantiomeric excesses (ee) for the 2e-derived enantiomers, (4S,5S)-2e ([!]220 = +1390
deg cm2 dmol–1) and (4R,5R)-2e ([!]220 = –1120 deg cm2 dmol–1) were isomerized into (4R,5S)-2e and
(4S,5R)-2e, respectively, in methanol containing TEA. The enantiomeric mixtures obtained were

HETEROCYCLES, Vol. 83, No. 6, 2011
1333
subjected to normal phase HPLC analysis, from which the retention times of the (4S,5S)-, (4R,5R)-,
(4R,5S)-, and (4S,5R)-enantiomers were estimated to be 15.4, 12.5, 7.1 and 8.8 min, respectively.8
Based on the area ratios of HPLC signals for the cis-2e- and trans-2e-derived enantiomers, the
asymmetric cyclization of (Z)-1e proceeding by the PET mechanism was found to produce (4R,5R)-2e (ee
= 19%) and (4R,5S)-2e (33%) in excess (Scheme 2). Enantiomeric composition analysis of cis-2f–h and
trans-2f–h was made in the same manner as described above.
Diastereoselective photocyclization
Table 1. Substituent, solvent, and tertiary amine effects on the photoreactivity of 1 and the de for cis-2 and trans-2,
obtained by the 3 h irradiation of (Z)-1 (4.0!10-3 mol dm-3) in the presence of TEA or DEAE (0.10 mol dm-3) at
room temperature
Composition and de (%)
cis-
2
trans-
2
de
Compound Solvent
Amine
TEA
de
(4S,5R)-2 (4R,5S)-2
(Z)-1 (E)-1 (4R,5R)-2 (4S,5S)-2
(Z)-1a
(Z)-1a
(Z)-1a
(Z)-1a
(Z)-1b
(Z)-1b
(Z)-1c
(Z)-1c
(Z)-1d
(Z)-1d
MeOH
9.3
2.5
21.8
3.4
29.3
26.2
8.9
24.0
29.1
6.2
10
5
8.8
23.1
30.7
19.8
7.0
6.8
15.7
21.2
15.0
5.0
13
19
18
14
17
8
ClCH2CH2Cl TEA
MeOH
DEAE
10.2
8.3
22.8
18.0
20.5
12.5
30.5
9.5
18
6
ClCH2CH2Cl DEAE
18.3
30.9
24.9
19.3
33.7
4.3
20.6
24.4
29.0
28.9
26.0
20.2
7.0
MeOH
ClCH2CH2Cl DEAE
MeOH DEAE
ClCH2CH2Cl DEAE
MeOH
DEAE
ClCH2CH2Cl DEAE
DEAE
12.2
7.6
12
8
14.0
3.4
12.0
6.9
11.0
4.5
20
13
65
17
34
35
71
81
8.5
17.8
16.4
26.8
20.2
29.2
36.1
29.2
2.8
5.0
2.8
In Table 1 are summarized the effects of substituent (chiral auxiliary), solvent, and tertiary amine on the
photoreactivity (conversion) of 1 and the de value of each diastereomer for cis-2 and trans-2. As can be
seen from the data of this Table, 2-(diethylamino)ethanol (DEAE) used instead of TEA showed a
tendency to increase both the de values estimated in methanol and 1,2-dichloroethane and, hence, is a
better tertiary amine for inducing higher diastereoselectivity, probably through hydrogen-bonding
interactions of both the amino nitrogen and hydroxy hydrogen in DEAE with 1 as well as with reaction
intermediate(s) involved. Interestingly, a change in solvent from methanol to 1,2-dichloroethane
reversed the configuration of major diastereomer for cis-2a without affecting it for trans-2a. If we
consider the great ability of methanol for hydrogen-bonding solvation, this interesting finding implies that
there is a difference in the asymmetric induction mechanism between these two solvents. Similar results
were obtained for the asymmetric photocyclization of 1b bearing an (S)-1-methylheptyl auxiliary. In a
previous study it has been found that an increase in the steric bulkiness of the alkyl group bonded to the
carboxy oxygen in N-benzoyl-!-dehydroarylalanine alkyl esters greatly enhances selectivity for the cis-
dihydrooxazole isomer.8 Since the PET-initiated cyclization reaction eventually forming cis- and trans-

1334
HETEROCYCLES, Vol. 83, No. 6, 2011
4,5-dihydrooxazole derivatives has been shown to be a kinetically-controlled process, this finding
stimulated us to introduce a more bulky auxiliary group into the ester moiety of (Z)-1. (–)-Menthyl and
(–)-8-phenylmenthyl groups were chosen as bulky auxiliaries. Careful diastereomer analysis of the
isolated products 2c and 2d revealed that the menthyl group influenced an asymmetric cyclization process
in a manner different from the sec-butyl group: In most cases the configuration of diastereomer formed in
excess was reversed and the de of this diastereomer was greatly enhanced particularly for the 2d-derived
diastereomers (de = 65% for cis-2d and 71% for trans-2d in methanol; de = 17% for cis-2d and 81% for
trans-2d in 1,2-dichloroethane). In addition, solvent effects on the composition ratio of (Z)-1 to (E)-1
showed that this ratio for 1d increases by a factor of about 2 on changing solvent from methanol to 1,2-
dichloroethane though minor solvent effects were observed for the (Z)-1a–c/(E)-1a–c composition
ratios. The presence of the bulky 8-phenylmenthyl group might exert a great effect not only on the
relative rates for isomerization of (Z)-1 and (E)-1 but also on the relative rate for the subsequent
cyclization reaction.
amine
(Z)-1
Back ET
ET
h!
h!
amine
(Z)-1
(Z)-1*
(Z)-I
amine
Ph
amine
OR
O
NH
ET
(E)-1 amine
(E)-1* amine
Ar
O
(E)-I
Path A1
Path A2
NH
Ph
Ph
amine
NH
amine
OR
O
O
OR
H
H
Ar
O
Ar
O
IIB
IIA
Back ET
Back ET
Ph
Ph
amine
OR
amine
OR
NH
NH
O
H
O
H
Ar
O
Ar
O
IIIA
IIIB
H shift
Path B2
H shift
Path C2
Path B1
Path C1
(4S,5S)-2
(4R,5S)-2
(4R,5R)-2
(4S,5R)-2
Scheme 3
Our attention is now directed to a mechanism for the PET-initiated asymmetric cyclization of (Z)-1. On
the basis of N-acyl substituent effects on the fluorescence intensity and photoreactivity of N-acyl-!-

HETEROCYCLES, Vol. 83, No. 6, 2011
1335
dehydroarylalanine tert-butyl esters, we have already proposed the radical ion pair intermediate (E)-I, as
shown in Scheme 3 (Ar = 1-naphthyl).8 In this Scheme the given chiral amine is considered to form a
hydrogen bond to the amide N–H hydrogen in 1. The occurrence of "-face selective intramolecular
cycloaddition in the (E)-1-derived radical anion (path A) is required for inducing asymmetry at 5-position
on the dihydrooxazole ring. This asymmetric cycloaddition can be considered to result in a preferential
formation of either the cyclized radical ion pair IIA or the IIB. There are two possible routes for the
subsequent back ET within the radical ion pair II. One is the transfer of an unpaired electron from 2-
position on the oxazole ring to the amine radical cation, which gives a zwitterion intermediate. The
other is the transfer of one of the paired electrons from 4-position on the oxazole ring to the amine radical
cation (see Scheme 3). The electron deficient carbon generated at 2-position on the ring of the
zwitterion should greatly promote the dissociation of the N–H proton. If so, intramolecular proton shift
in this zwitterion intermediate is unlikely to occur depending on the abilities of solvent and tertiary amine
to form hydrogen bonds. Thus, solvent and tertiary amine effects on the composition ratio of cis-2
to trans-2 favor the existence of the biradical intermediate III (Table 1). While "-face selective
cycloaddition in (E)-I induces asymmetry at 5-position on the oxazole ring of 2, asymmetric induction at
4-position on this ring is accomplished by preferential hydrogen shift in either the re or si face of III
(Paths B and C in Scheme 3). The simultaneous C=N bond formation may provide a driving force for
this hydrogen shift eventually leading to cis-2 and trans-2. The finding that the magnitude of de for 2a
as well as the composition ratio of cis-2a to trans-2a depends on the properties of the amine examined
suggests that the amino nitrogen and hydroxy hydrogen in DEAE form hydrogen bonds to the N–H
hydrogen and ester carbonyl oxygen in III, respectively, to exert an effect different from that caused
by TEA, as shown in Figure 2.
H
O
O
O
O
R
Ph
N
Ar
H
H
N
Et
Et
III
Figure 2. Schematic illustration for typical hydrogen-bonding interactions
between the biradical III and DEAE
Since hydrogen-bonding interaction of the intermediates (E)-I and III with methanol or DEAE plays a
key role in the control of de, temperature effects on the de value can be predicted to provide additional
information regarding our asymmetric induction mechanism. Inspection of the data collected in Table 2
confirmed that the de values of cis-2c and trans-2c in 1,2-dichloroethane were both increased with a
lowering of temperature whereas there was a sudden decrease in de (for these two dihydrooxazole
isomers) estimated in methanol at –78 °C. The former finding is consistent with the participation of

1336
HETEROCYCLES, Vol. 83, No. 6, 2011
Table 2. Temperature effects on the photoreactivity of 1c and the de values for cis-2c and trans-2c, obtained by
the 3 h or 1 h (–78 °C) irradiation of (Z)-1c (4.0!10-3 mol dm-3) in methanol and 1,2-dichloroethane containing
DEAE (0.10 mol dm-3)
Composition and de (%)
cis-2c
trans-2c
de
Solvent
Temperature (°C)
de (4S,5R)-2c (4R,5S)-2c
(Z)-1c (E)-1c (4R,5R)-2c (4S,5S)-2c
MeOH
MeOH
MeOH
50
rt
11.2
11.0
13.0
12.7
4.5
27.8
30.5
77.3
22.9
9.5
17.2
19.3
4.4
33.6
28.9
4.4
32
20
0
3.4
3.4
0.4
8.3
8.5
7.3
6.8
6.9
33
34
11
22
35
47
–78
0.5
ClCH2CH2Cl
ClCH2CH2Cl
50
rt
23.5
33.7
42.5
19.5
26.0
22.8
9
13.1
17.8
20.5
13
30
a
CH2Cl2
–78
2.0
4.9
a Since 1,2-dichloroethane is solidified at –78 °C, dichloromethane was used instead.
Table 3. Substituent and solvent effects on the composition of III and the rate ratio (Rr) of given
two competitive paths, obtained by the 3 h irradiation of (Z)-1 (4.0!10-3 mol dm-3) in the presence
of DEAE (0.10 mol dm-3)
Composition of III (%) and Rr
Temperature (°C)
Compound Solvent
Rr (C1/C2)
Rr (A1/A2) Rr (B1/B2)
IIIA
IIIB
(Z)-1a
(Z)-1b
(Z)-1c
MeOH
rt
rt
27.4
35.6
29.4
41.0
40.4
35.8
4.9
39.6
38.1
37.9
38.9
20.6
22.7
4.8
0.7
0.9
0.8
1.1
2.0
1.6
1.0
1.0
1.0
0.9
5.2
4.3
0.3
1.4
4.9
2.4
4.9
4.2
8.8
1.5
1.5
1.1
1.2
0.3
0.3
0.9
4.4
1.8
5.1
5.7
11.0
2.8
4.0
5.8
1.5
1.8
ClCH2CH2Cl
MeOH
rt
ClCH2CH2Cl
MeOH
rt
50
rt
MeOH
MeOH
–78
50
rt
ClCH2CH2Cl
ClCH2CH2Cl
CH2Cl2
32.6
43.8
43.3
36.6
33.8
31.8
42.2
49.8
7.1
–78
rt
(Z)-1d
MeOH
ClCH2CH2Cl
rt
7.8
hydrogen-bonding interaction between DEAE and III while the latter finding suggests that hydrogen-
bonding interaction of methanol with (E)-I is a factor controlling de in this protic solvent. The
intermediate (Z)-I should also be formed by ET from DEAE to (Z)-1* but its cyclization is unable
to proceed from the (Z)-configuration to afford the corresponding intermediate II (Scheme 3). Thus, we

HETEROCYCLES, Vol. 83, No. 6, 2011
1337
are able to speculate that (Z)-I undergoes an exclusive back ET to regenerate (Z)-1 and DEAE. In
addition to mechanistic information obtained from a previous study,8 these considerations render the
asymmetric induction mechanism shown in Scheme 3 reasonable further, in which asymmetry at 5- and
4-positions on the dihydrooxazole ring is induced at the stages of the II-forming cycloaddition and the
hydrogen shift in III, respectively.
It is possible to estimate the compositions of IIIA and IIIB (or IIA and IIB), as well as the rate ratios of
paths A, B, and C, on the basis of the composition of each diastereomer for cis-2 and trans-2 collected
in Table 1, because configurational interconversion between IIIA and IIIB or between IIA and IIB is
very unlikely to occur during irradiation (Table 3). A comparison between the compositions of IIIA and
IIIB thus estimated shows that asymmetric induction for 1a–c in 1,2-dichloroethane is achieved at the
stage of hydrogen shift in the biradical III while a difference in the radical ion pair II-forming cyclization
rate is mainly responsible for the asymmetric induction in methanol. Since rate ratios for paths B and C
depend on chiral auxiliary and temperature in any solvents, hydrogen-bonding and steric interactions of
DEAE with IIIA and IIIB may change the relative rates of paths B1 and C1 and paths B2 and C2 (to a
different extent) in the process of hydrogen shift in III. In the "-face selective intramolecular
cycloaddition, both the steric bulkiness of chiral auxiliary and the hydrogen-bonding solvation of the
radical ion pair (E)-I by methanol are considered to cause the difference in rate for paths A1 and
A2. Surprisingly, the introduction of a (–)-8-phenylmenthyl auxiliary group resulted in a considerable
increase in the relative composition of IIIA in any solvents examined. This suggests that steric
repulsion between the bulky chiral auxiliary and the N-benzoyl carbonyl oxygen in the radical ion pair
intermediate (E)-I is a dominant factor controlling the relative rate of path A, irrespective of the solvent
properties. The fact that the cyclized radical ion pair IIA is formed in excess proves that the bulky
phenylmenthyl group exists preferentially in the si face of the intermediate (E)-I to cause cycloaddition in
the re face of this intermediate. On the other hand, the observation of much lower de (than expected) for
cis-2d in 1,2-dichloroethane must be related to the greatly diminished relative rate of path B1. In this
aprotic solvent the presence of the bulky phenylmenthyl group may slow down the rate of hydrogen shift
in the re face of the biradical intermediate IIIA.
Enantioselective photocyclization
In the preceding section we demonstrated that asymmetric induction in the PET-initiated cyclization of
(Z)-1a–d eventually affording the corresponding 3,4-dihydrooxazole derivatives was achieved at the
stages of the II-forming intramolecular cycloaddition as well as the hydrogen shift in III. At the former
stage the steric bulkiness of a given chiral auxiliary group played a great role in the control of de, whereas
hydrogen-bonding interaction between III and DEAE was a major factor governing the magnitude of de
at the latter stage. As already described, aliphatic amines such as DEAE and TEA may interact directly
with this biradical intermediate, so that the presence of a chiral amine is supposed to bring about the
asymmetric cyclization of (Z)-1 having no chiral auxiliary and also to unravel the role of the amine-
derived radical cation intermediate in the II-forming cyclization process.
While irradiation of a nitrogen-saturated 1,2-dichloroethane solution of (Z)-1e containing each chiral

1338
HETEROCYCLES, Vol. 83, No. 6, 2011
amine afforded quantitatively the corresponding dihydrooxazole derivative 2e, a small amount of this
derivative was only detected on irradiating its methanol solution under the same conditions (Scheme 2).
Much higher photoreactivity of N-benzoyl-!-dehydroarylalanine alkyl esters in 1,2-dichloroethane than
in methanol indicates that chiral amines given in Chart 1 have lower electron donating abilities and
also are subject to stronger hydrogen-bonding solvation in methanol, as compared to TEA.8 In Table 4
are summarized the effects of substituent and chiral amine on the magnitude of ee for cis-2e and trans-2e
Table 4. Substituent and chiral amine effects on the selectivity of each enantiomer and the ee values
for cis-2 and trans-2, obtained by the 6 h irradiation of (Z)-1 (4.0!10–3 mol dm–3) in 1,2-dichloroethane
containing chiral amine (0.10 mol dm–3) at room temperature
Compositionb and ee (%)
cis-
2
trans-
2
Compound Chiral amine Conversion (%)a
(4R,5R)-2 (4S,5S)-2
ee
(4S,5R)-2 (4R,5S)-2 ee
(Z)-1e
(Z)-1e
(Z)-1e
(Z)-1e
(Z)-1f
(Z)-1g
(Z)-1h
S-PG
95
97
18.6
13.0
23.8
36.6
33.4
26.6
24.2
23.4
23.6
12.8
24.8
23.6
12.5
10.8
11
29
30
19
17
36
38
30.7
37.1
26.3
12.9
16.0
24.4
26.0
27.3
26.3
37.1
25.7
27.0
36.5
39.0
6
17
17
33
26
20
20
S-PM
R-PM
97
S-MPM
S-MPM
S-MPM
S-MPM
100
100
100
100
a Conversion was estimated by dividing the sum of compositions for cis-2 and trans-2 by the sum
of compositions for (Z)-1, (E)-1, cis-2, and trans-2.
b Composition of each enantiomer for cis-2 and trans-2 was evaluated by dividing the composition
for each enantiomer by the sum of compositions for cis-2 and trans-2.
formed in 1,2-dichloroethane. Examination of the amine effects on the ee confirmed that the ability
to induce the asymmetric cyclization was lowered in the order of S-MPM " S-PM > S-PG and R-PM used
instead of S-PM gave enantiomers having inverse configurations, namely (4R,5R)-2e and (4R,5S)-2e in
excess. Since this order mainly reflects the difference in basicity among these chiral amines, S-MPM
was chosen as a chiral amine for investigating the substituent and temperature effects on the ee
value. The replacement of an 1-naphthyl group by a phenyl or a 2-naphthyl enhanced the ee value for
cis-2 with a decrease in this value for the trans-isomer, whereas the introduction of a less bulky
methoxycarbonyl group into the tert-butoxycarbonyl moiety of (Z)-1e exerted a minor steric effect on the
ee for both the cis- and trans-dihydrooxazole isomers. As described above, we proposed steric
interaction between the chiral auxiliary groups and the N-benzoyl carbonyl oxygen in the cycloaddition
process of II as well as hydrogen-bonding interaction between III and the tertiary amines, as control
factors of de (Scheme 3). Thus, the slight steric effect of the alkoxycarbonyl group suggests that "-face
selective cycloaddition in (E)-I takes place to only a minor extent and also the S-MPM-derived radical

HETEROCYCLES, Vol. 83, No. 6, 2011
1339
cation is not actively involved in this II-forming cycloaddition process. Moreover, the aryl substituent
effect on the ee value provides additional evidence for the PET-initiated asymmetric cyclization
mechanism shown in Scheme 3 (Ar = 1-naphthyl, 2-naphthyl or phenyl), where the steric bulkiness of an
aryl group attached to 5-position on the dihydrooxazole ring affects hydrogen shifts in the re and si faces
of the biradical intermediate III to a different extent. It is likely that this intermediate (hydrogen bonded
to a given chiral amine) adopts different conformations depending on steric and electronic interactions
among unpaired electrons, heteroatoms, and alkoxycarbonyl and aryl groups.
Since hydrogen-bonding interaction between the intermediate III and the chiral amine was shown to be
one of the factors controlling the magnitude of ee for the cyclized product 2, it is expected that ee for cis-
2e and trans-2e estimated in 1,2-dichloroethane containing S-MPM is increased as temperature is lowered
and also increased with an increase in the S-MPM concentration. Contrary to our expectation, ee for
trans-2e, i.e., (4R,5S)-2e exhibited a very small temperature dependence while ee for cis-2e, i.e., (4R,5R)-
2e had a tendency to decrease with a drop in temperature ([(Z)-1e] = 4.0"10–3 mol dm–3, [S-MPM] = 0.10
mol dm–3): ee for (4R,5R)-2e = 21% (50 °C), 19% (room temperature, Table 4), 10% (–78 °C, CH2Cl2)
and ee for (4R,5S)-2e = 30% (50 °C), 33% (room temperature, Table 4), and 28% (–78 °C). On the
basis of these temperature effects on the ee value, we propose that the hydrogen-bonded biradical
intermediate adopts a temperature-dependent conformation. A drop in temperature is very likely
to affect hydrogen shifts in the re and si faces of III to a similar extent. On the other hand, an increase
in the concentration of S-MPM enhanced not only the conversion of 1e but also the magnitude of ee for
both the enantiomers (Table 5). These findings are consistent with our expectation and, hence, provide
evidence supporting not only the involvement of the hydrogen-bonding interaction as a control factor of
ee, but also the participation of a PET mechanism.
Table 5. Concentration effects of S-MPM on the conversion of 1e and the ee values for cis-2e
and trans-2e, obtained by the 6 h irradiation of (Z)-1e (4.0!10–3 mol dm–3) in 1,2-dichloroethane
containing this chiral amine at room temperature
Composition and ee (%)
(Z)-1e (E)-1e
cis-2e
trans-2e
[S-MPM] Conversion
(mol dm–3)
(%)
ee (4S,5R)-2e (4R,5S)-2e ee
(4R,5R)-2e (4S,5S)-2e
0.010
0.050
0.10
43
58
24.7
18.1
0
32.0
24.4
0
8.1
13.7
36.6
6.8
10.1
24.8
9
15
19
12.5
12.5
12.9
15.9
21.2
25.7
12
26
33
100
According to the same procedures as those employed in the preceding section, both the compositions of
IIIA and IIIB (or IIA and IIB) and the rate ratios of paths A, B and C were estimated from the
composition of each enantiomer for cis-2e–h and trans-2e–h collected in Table 4 (Table 6). As already
predicted, rate ratios for the IIA- and IIB-forming cyclization processes, paths A1 and A2, were unity
irrespective of !-dehydroarylalanine alkyl esters and reaction temperatures tested, thus allowing us

1340
HETEROCYCLES, Vol. 83, No. 6, 2011
to conclude that asymmetry at 4-position on the 4,5-dihydrooxazole ring is induced at the stage of
hydrogen shifts within the hydrogen-bonded biradical intermediates IIIA and IIIB. The chiral amine-
derived radical cation is considered to play only a minor role in inducing asymmetry at 5-position on the
ring, namely, in inducing "-face selective cycloaddition within the radical ion pair intermediate (E)-I. In
addition, analysis of the substituent effects on the Rr (B1/B2) and Rr (C1/C2) values led us to assume that
Table 6. Substituent, chiral amine and temperature effects on the composition of III and the rate
ratio (Rr) of given two competitive paths, obtained by the irradiation of (Z)-1 in the presence of
the amine
Composition of III (%) and Rr
IIIA
IIIB
Rr (C1/C2)
Rr (A1/A2) Rr (B1/B2)
Compound Chiral amine Temperature (°C)
S-MPM
S-MPM
S-MPM
S-MPM
S-MPM
S-MPM
S-PG
rt
rt
50.5
50.6
49.0
49.8
49.3
50.7
50.7
49.9
49.5
49.4
51.0
50.2
50.7
49.3
49.3
50.1
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
0.9
0.3
0.3
1.0
1.6
0.9
0.9
2.8
2.1
1.1
0.9
2.8
3.5
0.6
0.4
(Z)-1e
(Z)-1f
(Z)-1g
(Z)-1h
(Z)-1e
(Z)-1e
(Z)-1e
(Z)-1e
rt
rt
50
–78
rt
S-PM
rt
both the alkoxycarbonyl groups in IIIA and IIIB exist preferentially in the re face and exert steric effects
on the hydrogen shift in this face resulting in an excess of (4R,5R)-2 and (4R,5S)-2. It is quite likely that
steric and electronic interactions among unpaired electrons, heteroatoms, and alkoxycarbonyl and aryl
groups in these two biradical intermediates determine their most stable conformations. Interestingly,
when the primary and secondary chiral amines S-PG and S-PM were used instead of the tertiary amine S-
MPM, the cis- and trans-enantiomers formed in excess changed from (4R,5R)-2e and (4R,5S)-2e
to (4S,5S)-2e and (4S,5R)-2e, respectively (Table 4). The fact that all of the Rr (A1/A2) values for S-
PG, S-PM and S-MPM are unity substantiates an alteration in the mode of hydrogen-bonding interaction
R
Ph
O
O
O
H
H
Ph
N
N
H
Ar
O
H
Me
O
Ar
H
N
H
N
O
O
R
H
H
O
H
III
Figure 3. Schematic illustration for typical hydrogen-bonding interactions of the biradical III with S-
MPM and S-PM

HETEROCYCLES, Vol. 83, No. 6, 2011
1341
between III and these chiral amines (Table 6). As typically depicted in Figure 3, we propose that
while S-MPM assists hydrogen shift in the si face (through hydrogen bonds formed between the amine
N–Me nitrogen and the N–H hydrogen in III as well as between the amine O–H hydrogen and the ester
carbonyl oxygen in III), S-PG and S-PM partially block this face through similar type of hydrogen bonds
to promote hydrogen shift in the re face.
CONCLUSION
The steric effects of chiral auxiliary and 1-naphthyl groups on the hydrogen-bonding interaction between
DEAE and the biradical intermediate III as well as on the hydrogen-bonding solvation and "-face
selective intramolecular cycloaddition of the radical ion pair intermediate (E)-I were shown to be major
controlling factors of de for the PET-initiated asymmetric cyclization of (Z)-1a–d. In addition, the
introduction of a (–)-8-phenylmenthyl auxiliary group induced a large asymmetry at the stage of the II-
forming cyclization process, irrespective of the solvation ability of the solvent tested. A large steric
repulsion between the chiral auxiliary group introduced and the N-benzoyl carbonyl oxygen in the radical
ion pair intermediate (E)-I was proposed in order to explain the "-face selective cycloaddition of this
carbonyl oxygen to the olefinic carbon of (E)-I. On the other hand, the chiral auxiliary-unsubstituted
derivatives (Z)-1e–h were found to undergo enantioselective photocyclization reactions in the presence of
chiral aliphatic amines such as S-PM and S-MPM. On the basis of the substituent, chiral amine, and
temperature effects on the ee values for cis-2e and trans-2e, we were led to conclude that while the chiral
amine-derived radical cation plays only a minor role in the II-forming cycloaddition process, hydrogen-
bonding interactions between the biradical intermediate III and the chiral amine enables asymmetric
hydrogen shift within this intermediate.
EXPERIMENTAL
General
1H and 13C NMR spectra were taken with a JEOL JNM-ECA500 or a JEOL JNM-ECA600 spectrometer.
Chemical shifts were determined using tetramethylsilane as an internal standard. IR spectra were
recorded on a SHIMADZU IRPrestige-21 infrared spectrophotometer. HPLC analysis was performed
on a SHIMADZU LC-10AT (for separation and quantification) or a SHIMADZU LC-8A (for separation
and isolation) high-performance liquid chromatography system equipped with a 4.6"150-mm Daicel
Chiralcel OD-RH column (for quantification of trans-diastereomer), a 4.6"250-mm Daicel Chiralpak IA
column (for quantification of enantiomer) or a 10"250-mm Daicel Chiralcel OJ column (for isolation of
enantiomer) and a SHIMADZU SPD-10A UV detector [detection wavelength = 250 nm; mobile phase,
MeCN:H2O = 3:1 v/v (for quantification of diastereomer), i-PrOH:CHCl3:n-C6H12 = 1:1:18 v/v (for
quantification of enantiomer) or i-PrOH:n-C6H12 = 1:5 v/v (for isolation of enantiomer)]. UV absorption
spectra were recorded on a HITACHI U-3300 spectrophotometer. A cell with a 10-mm pathlength was
used. Circular dichroism spectra were recorded on a NIHONBUNKO J-600 spectropolarimeter.
Optical rotations were measured with a NIHONBUNKO P-1020 polarimeter. Elemental analyses were
performed on a PERKIN-ELMER PE2400 series II CHNS/O analyzer. Mass spectra were taken with a

1342
HETEROCYCLES, Vol. 83, No. 6, 2011
JEOL JMS-01 SG-2 spectrometer. MeOH was purified according to the standard procedure and freshly
distilled prior to use.9 1,2-Dichloroethane and dichloromethane were of spectroscopic grade and used as
received. TEA and DEAE were fractionally distilled from sodium hydroxide. All other reagents
including chiral amines were obtained from commercial sources and were of the highest grade available.
General procedure for the synthesis of (Z)-4-(1-naphthylmethylene)-2-phenyl-5(4H)-oxazolone, (Z)-
4-(2-naphthylmethylene)-2-phenyl-5(4H)-oxazolone
and
(Z)-4-benzylidene-2-phenyl-5(4H)-
oxazolone
N-Benzoylglycine (50 mmol), 1-naphthaldehyde, 2-naphthaldehyde or benzaldehyde (50 mmol), and
sodium acetate (20 mmol) were added to acetic anhydride (10–30 mL) and the resulting mixture was
heated at 65–75 °C for 1–2 h with stirring. The mixture was cooled with ice and the solid separated out
was collected by filtration with suction and washed with water, a small amount of cold EtOH, and then
with dry hexane. After the crude product had been air-dried at room temperature, it was recrystallized
from hexane-CHCl3 to give yellow crystals (61–74%).
(Z)-4-(1-Naphthylmethylene)-2-phenyl-5(4H)-oxazolone: mp 166.0–167.0 °C; IR (KBr) #/cm–1 = 1797,
1647, 1167; 1H NMR (500 MHz, CDCl3) $ = 7.54 (2H, dd, J = 7.3, 7.6 Hz), 7.55 (1H, dd, J = 8.6, 8.6 Hz),
7.62 (1H, dd, J = 7.3, 7.3 Hz), 7.63 (1H, dd, J = 8.6, 8.6 Hz), 7.64 (1H, dd, J = 6.7, 8.6 Hz), 7.90 (1H, d, J
= 8.6 Hz), 7.97 (1H, d, J = 8.6 Hz), 8.13 (1H, s), 8.21 (2H, d, J = 7.6 Hz), 8.31 (1H, d, J = 8.6 Hz), 9.03
(1H, d, J = 6.7 Hz).
(Z)-4-(2-Naphthylmethylene)-2-phenyl-5(4H)-oxazolone: mp 142.0–143.0 °C; IR (KBr) #/cm–1 = 1797,
1626, 1167; 1H NMR (500 MHz, CDCl3) $ = 7.51 (1H, dd, J = 7.9, 7.9 Hz), 7.54 (1H, dd, J = 7.9, 7.9 Hz),
7.54 (2H, dd, J = 7.9, 7.9 Hz), 7.61 (1H, dd, J = 7.9, 7.9 Hz), 7.83 (1H, d, J = 7.9 Hz), 7.89 (1H, d, J =
8.5 Hz), 7.91 (1H, d, J = 7.9 Hz), 8.19 (2H, d, J = 7.9 Hz), 8.43 (1H, s), 8.49 (1H, d, J = 8.5 Hz).
(Z)-4-Benzylidene-2-phenyl-5(4H)-oxazolone: mp 162.0–163.0 °C; IR (KBr) #/cm–1 = 1779, 1659,
1266; 1H NMR (500 MHz, CDCl3) $ = 7.25 (1H, s), 7.47 (2H, dd, J = 7.4, 8.0 Hz), 7.49 (1H, dd, J = 7.4,
7.4 Hz), 7.54 (2H, dd, J = 7.2, 7.4 Hz), 7.62 (1H, dd, J = 7.4, 7.4 Hz), 8.19 (2H, d, J = 8.0 Hz), 8.21 (2H,
d, J = 7.2 Hz).
General procedure for the synthesis of alkyl (Z)-2-benzoylamino-3-(1-naphthyl)-2-propenoates and
tert-butyl (Z)-3-aryl-2-benzoylamino-2-propenoates
(Z)-4-(1-Naphthylmethylene)-2-phenyl-5(4H)-oxazolone
(for
1a–f,
10
mmol),
(Z)-4-(2-
naphthylmethylene)-2-phenyl-5(4H)-oxazolone (for 1g, 10 mmol) or (Z)-4-benzylidene-2-phenyl-5(4H)-
oxazolone (for 1h, 10 mmol) was added to an 1,2-dichloroethane solution (60 mL) containing a given
chiral alcohol (for 1a–d, 30 mmol) and 4-(dimethylamino)pyridine (20 mmol) or to an achiral alcohol
solution (for 1e–h, 60 mL) containing 4-(dimethylamino)pyridine (20 mmol), and the resulting mixture
was refluxed for 1–2 h. After removal of the solvent under reduced pressure, the residual solid obtained

HETEROCYCLES, Vol. 83, No. 6, 2011
1343
was dissolved in CHCl3 (50–100 mL) and then washed twice with hydrochloric acid (0.5 mol dm–3, 50
mL) and finally dried over sodium sulfate. Evaporation of chloroform in vacuo gave the crystalline
solid which was recrystallized from EtOAc–hexane affording colorless crystals (47–92%). In order
to purify the crude products, column chromatography on silica gel was also used.
(S)-sec-Butyl (Z)-2-benzoylamino-3-(1-naphthyl)-2-propenoate [(Z)-1a]: mp 113.5–114.5 °C; IR
25
1
(KBr) #/cm–1 = 3336, 1654, 1577; [%]D +20.2° (c = 0.5, MeOH); H NMR (600 MHz, DMSO-d6) $ =
0.89 (3H, t, J = 7.6 Hz), 1.24 (3H, d, J = 6.2 Hz), 1.59 (2H, dq, J = 6.9, 7.6 Hz), 4.90 (1H, tq, J = 6.2, 6.9
Hz), 7.45 (2H, dd, J = 7.6, 8.3 Hz), 7.50 (1H, dd, J = 6.9, 8.3 Hz), 7.53 (1H, dd, J = 7.6, 7.6 Hz), 7.55–
7.59 (2H, m), 7.70 (1H, d, J = 6.9 Hz), 7.81 (2H, d, J = 7.6 Hz), 7.87 (1H, s), 7.92 (1H, d, J = 8.3 Hz),
7.95 (1H, d, J = 8.3 Hz), 7.99 (1H, d, J = 8.3 Hz), 9.95 (1H, s); 13C NMR (150 MHz, DMSO-d6) $ = 9.4,
19.1, 28.2, 72.9, 124.0, 125.4, 126.2, 126.6, 126.7, 127.6 (2C), 128.3 (2C), 128.5, 129.1, 129.2, 129.7,
130.5, 130.9, 131.7, 133.2, 133.5, 166.4, 166.5. Anal. Calcd for C24H23NO3: C, 77.19; H, 6.21; N, 3.75.
Found: C, 77.18; H, 6.23; N, 3.46.
(S)-2-Octyl (Z)-2-benzoylamino-3-(1-naphthyl)-2-propenoate [(Z)-1b]: mp 104.0–105.0 °C; IR (KBr)
25
1
#/cm–1 = 3398, 1666; [%]D +58.1 (c 0.5, MeOH); H NMR (600 MHz, DMSO-d6) $ = 0.82 (3H, t, J =
6.9 Hz), 1.14–1.35 (8H, m), 1.25 (3H, d, J = 6.2 Hz), 1.49–1.60 (2H, m), 4.94 (1H, tq, J = 6.2, 6.2 Hz),
7.44 (2H, dd, J = 7.6, 7.6 Hz), 7.49 (1H, dd, J = 6.9, 8.3 Hz), 7.53 (1H, dd, J = 7.6, 7.6 Hz), 7.54–7.59
(2H, m), 7.70 (1H, d, J = 6.9 Hz), 7.81 (2H, d, J = 7.6 Hz), 7.87 (1H, s), 7.92 (1H, d, J = 8.3 Hz), 7.94–
7.96 (1H, m), 7.99 (1H, d, J = 6.9 Hz), 9.96 (1H, s); 13C NMR (150 MHz, DMSO-d6) $ = 13.9, 19.6, 22.0,
24.5, 28.5, 31.1, 35.3, 71.7, 123.9, 125.4, 126.1, 126.6, 126.7, 127.6 (2C), 128.3 (2C), 128.6, 129.1, 129.2,
129.7, 130.5, 131.0, 131.7, 133.2, 133.4, 164.5, 166.5. Anal. Calcd for C28H31NO3: C, 78.29; H, 7.27; N,
3.26. Found: C, 78.62; H, 7.20; N, 3.47.
(1R,2S,5R)-(–)-Menthyl (Z)-2-benzoylamino-3-(1-naphthyl)-2-propenoate [(Z)-1c]: mp 126.0–127.0
25
1
°C; IR (KBr) #/cm–1 = 3350, 1672, 1639; [%]D –32.2 (c 0.5, MeOH); H NMR (600 MHz, DMSO-d6)
$ = 0.78 (3H, d, J = 6.9 Hz), 0.81 (3H, d, J = 6.9 Hz), 0.82–2.06 (9H, m), 0.90 (3H, d, J = 6.9 Hz), 4.71
(1H, ddd, J = 6.9, 6.9, 6.9 Hz), 7.45 (2H, dd, J = 7.5, 7.5 Hz), 7.50 (1H, dd, J = 7.5, 7.5 Hz), 7.53–7.60
(3H, m), 7.71 (1H, d, J = 7.5 Hz), 7.79 (2H, d, J = 7.5 Hz), 7.89 (1H, s), 7.93 (1H, d, J = 8.6 Hz), 7.95–
13
7.98 (2H, m), 9.94 (1H, s); C NMR (150 MHz, DMSO-d6) $ = 16.3, 20.6, 21.9 (2C), 23.0, 25.6, 30.9,
33.7, 40.0, 40.4, 46.6, 74.7, 123.9, 125.5, 126.2, 126.7, 127.6 (2C), 128.3 (2C), 128.6, 129.2, 129.6, 130.4,
130.9, 131.7, 133.2, 133.5, 164.4, 166.6. Anal. Calcd for C30H33NO3: C, 79.09; H, 7.30; N, 3.03. Found:
C, 79.48; H, 7.35; N, 3.07.
(1R,2S,5R)-(–)-8-Phenylmenthyl (Z)-2-benzoylamino-3-(1-naphthyl)-2-propenoate [(Z)-1d]: mp
135.0–135.5 °C; IR (KBr) #/cm–1 = 3311, 1701, 1657; [%]D25 +169.5 (c 0.1, MeOH); 1H NMR (600 MHz,
DMSO-d6) $ = 0.81–0.84 (1H, m), 0.87 (3H, d, J = 6.3 Hz), 1.03–1.16 (2H, m), 1.26 (3H, s), 1.39 (3H, s),
1.41–1.44 (2H, m), 1.53–1.55 (1H, m), 1.96–1.98 (1H, m), 2.07–2.10 (1H, m), 4.83 (1H, ddd, J = 6.9, 6.9,

1344
HETEROCYCLES, Vol. 83, No. 6, 2011
6.9 Hz), 6.91 (1H, dd, J = 7.5, 7.5 Hz), 7.20 (2H, dd, J = 7.5, 7.5 Hz), 7.33 (2H, d, J = 7.5 Hz), 7.45 (2H,
dd, J = 7.5, 7.5 Hz), 7.47 (1H, dd, J = 7.5, 7.5 Hz), 7.50 (1H, s), 7.51–7.60 (3H, m), 7.65 (1H, d, J = 7.5
Hz), 7.80 (2H, d, J = 7.5 Hz), 7.86 (1H, d, J = 8.0 Hz), 7.90 (1H, d, J = 7.5 Hz), 7.94 (1H, d, J = 8.0 Hz),
9.76 (1H, s); 13C NMR (150 MHz, DMSO-d6) $ = 20.7 (2C), 20.9, 22.2 (2C), 24.8, 26.1, 28.5, 34.3, 38.6,
46.2, 71.6, 123.9, 124.2, 125.5, 126.3, 126.86, 126.89, 127.61 (2C), 128.0, 128.4 (2C), 128.7, 129.4,
129.6, 130.2, 130.41, 130.43, 131.0, 131.8, 132.2, 132.6, 133.6, 164.3, 166.8. Anal. Calcd for C36H37NO3:
C, 81.32; H, 7.01; N, 2.63. Found: C, 81.50; H, 6.98; N, 2.51.
tert-Butyl (Z)-2-benzoylamino-3-(1-naphthyl)-2-propenoate [(Z)-1e]: mp 120.0–121.0 °C; IR (KBr)
1
#/cm–1 = 3289, 1709, 1638; H NMR (500 MHz, DMSO-d6) $ = 1.50 (9H, s), 7.45 (2H, dd, J = 7.6, 8.2
Hz), 7.50 (1H, dd, J = 6.9, 8.2 Hz), 7.54 (1H, dd, J = 7.6, 7.6 Hz), 7.58 (1H, dd, J = 6.9, 8.2 Hz), 7.59 (1H,
dd, J = 6.9, 7.6 Hz), 7.68 (1H, d, J = 6.9 Hz), 7.81 (2H, d, J = 8.2 Hz), 7.82 (1H, s), 7.92 (1H, d, J = 8.2
Hz), 7.96 (1H, d, J = 7.6 Hz), 8.01 (1H, d, J = 8.2 Hz), 9.88 (1H, s); 13C NMR (125 MHz, DMSO-d6) $ =
27.6 (3C), 80.7, 124.0, 125.4, 126.0, 126.5 (2C), 127.5 (2C), 128.2 (2C), 128.4, 128.6, 128.9, 130.4,
130.7, 130.9, 131.5, 133.1, 133.6, 163.7, 166.5. Anal. Calcd for C24H23NO3: C, 77.19; H, 6.21; N, 3.75.
Found: C, 77.35; H, 6.29; N, 3.74.
Methyl (Z)-2-benzoylamino-3-(1-naphthyl)-2-propenoate [(Z)-1f]: mp 118.0–118.5 °C; IR (KBr)
1
#/cm–1 = 3200, 1732, 1632; H NMR (500 MHz, DMSO-d6) $ = 3.80 (3H, s), 7.46 (2H, dd, J = 7.6, 7.6
Hz), 7.51 (1H, dd, J = 7.6, 8.9 Hz), 7.55 (1H, dd, J = 7.6, 7.6 Hz), 7.58 (1H, dd, J = 6.9, 6.9 Hz), 7.59 (1H,
dd, J = 6.9, 7.6 Hz), 7.69 (1H, d, J = 7.6 Hz), 7.84 (2H, d, J = 7.6 Hz), 7.90 (1H, s), 7.94 (1H, d, J = 8.9
Hz), 7.97 (1H, d, J = 6.9 Hz), 8.05 (1H, d, J = 7.6 Hz), 10.0 (1H, s); 13C NMR (125 MHz, DMSO-d6): $ =
52.3, 124.1, 125.4, 126.2, 126.62, 126.65, 127.6 (2C), 128.3 (2C), 128.5, 128.9, 129.2, 129.9, 130.5,
131.0, 131.8, 133.15, 133.22, 165.3, 166.4. Anal. Calcd for C21H17NO3: C, 76.12; H, 5.17; N, 4.23.
Found: C, 75.88; H, 4.98; N, 4.19.
tert-Butyl (Z)-2-benzoylamino-3-(2-naphthyl)-2-propenoate [(Z)-1g]: mp 169.0–170.0 °C; IR (KBr)
#/cm–1 = 3323, 1707, 1660; 1H NMR (500 MHz, DMSO-d6) $ = 1.48 (9H, s), 7.49 (1H, s), 7.51–7.56 (4H,
m), 7.61 (1H, dd, J = 7.4, 7.4 Hz), 7.82 (1H, d, J = 8.6 Hz), 7.86-7.91 (3H, m), 7.98 (2H, d, J = 7.4 Hz),
8.19 (1H, s), 10.1 (1H, s); 13C NMR (125 MHz, DMSO-d6) $ = 28.5 (3C), 81.5, 126.9, 127.4, 127.9,
128.3, 128.4 (2C), 128.7, 129.1, 129.2, 129.3 (2C), 131.1, 132.2, 132.6, 132.7, 133.5, 133.8, 134.5, 164.9,
167.2. Anal. Calcd for C24H23NO3: C, 77.19; H, 6.21; N, 3.75. Found: C, 77.02; H, 6.19; N, 3.70.
tert-Butyl (Z)-2-benzoylamino-3-phenyl-2-propenoate [(Z)-1h]: mp 144.0–145.0 °C; IR (KBr) #/cm–1
= 3248, 1709, 1641; 1H NMR (500 MHz, DMSO-d6) $ = 1.44 (9H, s), 7.31 (1H, s), 7.34 (1H, dd, J = 7.5,
7.5 Hz), 7.40 (2H, dd, J = 7.5, 7.5 Hz), 7.51 (2H, dd, J = 7.5, 7.5 Hz), 7.60 (1H, dd, J = 7.5, 7.5 Hz), 7.65
(2H, d, J = 7.5 Hz), 7.95 (2H, d, J = 7.5 Hz), 9.98 (1H, s); 13C NMR (125 MHz, DMSO-d6) $ = 27.1 (3C),
80.1, 127.1 (2C), 127.7, 127.9 (2C), 128.1 (2C), 128.7, 129.2 (2C), 131.2, 131.4, 133.15, 133.19, 163.5,
165.8. Anal. Calcd (found) for C20H21NO3: C, 74.28; H, 6.55; N, 4.33. Found: C, 74.11; H, 6.21; N, 4.43.

HETEROCYCLES, Vol. 83, No. 6, 2011
1345
General procedure for the irradiation of (Z)-1a–h
For the purpose of analyzing the effects of chiral auxiliary, substituent, aliphatic amine, and solvent on
the magnitude of de or ee, nitrogen-saturated MeOH or 1,2-dichloroethane solutions (10 mL) of (Z)-1
(4.0"10-3 mol dm-3) containing a given aliphatic amine (0.10 mol dm-3), placed in a sealed tube, were
irradiated in parallel for a given period of time with a 400 W high-pressure Hg lamp set in a Pyrex
cooling jacket. Parallel irradiation of the solutions was done on a merry-go-round apparatus (RIKO
model RH400-10W) immersed into a water bath. After the irradiation, each solution was concentrated
to dryness in vacuo. The resulting residue was dissolved in DMSO-d6 and n-C6H12-CHCl3 (95:5 v/v)
1
and subjected to H NMR spectral and HPLC analyses, respectively. The aliphatic amine of high
boiling point was removed by treating it with diluted hydrochloric acid before these spectral and
chromatographic analyses. Temperature effects on the de and ee values were accomplished by
irradiating a nitrogen-saturated MeOH or CH2Cl2 solution (4.0"10-3 mol dm-3, 50 mL), placed in a Pyrex
vessel thermostated at 50 or –78 °C, with a 400 W high-pressure Hg lamp.
On the other hand, a nitrogen-saturated MeOH or 1,2-dichloroethane solution of (Z)-1 (4.0"10–3 mol dm–3,
500 mL) containing achiral or chiral amine (0.10 mol dm–3), placed in a Pyrex vessel, was irradiated for a
given period of time with Pyrex-filtered light from a 400 W high-pressure Hg lamp at room temperature.
After the irradiation, an aliquot (5 mL) of the solution was pipetted off and concentrated to dryness in
1
vacuo. The resulting residue was dissolved in DMSO-d6 and subjected to H NMR spectral
1
analysis. The composition was estimated from the area ratio of a given H NMR signal for each
compound. The remaining solution was concentrated to dryness under reduced pressure and the
resulting residue was subjected to column chromatography on silica gel (230 mesh, Merck) eluting with
CHCl3-EtOAc or hexane-EtOAc. For the purpose of isolating the photoproducts, preparative TLC plate
(silica gel) and HPLC chiral column were also used. Physical and spectroscopic data of (E)-1a and
diastereomers derived from cis- and trans-4,5-dihydrooxazoles (cis- and trans-2a–d) are as follows. In
addition, the dihydrooxazole isomers cis- and trans-2e–h were isolated and characterized as enantiomeric
mixtures. To determine the absolute configuration of each enantiomer and the retention time of its
HPLC signal, cis-2e (30 mg) was dissolved in 2-propanol (10 mL) and separated into (4S,5S)-2e and
(4R,5R)-2e by normal-phase HPLC using 2-propanol-hexane (1:5 v/v) as a mobile phase. The
isomerization of (4S,5S)-2e and (4R,5R)-2e into the corresponding (4R,5S)- and (4S,5R)-enantiomers was
accomplished by allowing a methanol solution of the former cis-enantiomer containing TEA (0.10 mol
dm–3) to stand for 10 days at room temperature. The latter trans-enantiomer formed was separated and
purified by preparative thin-layer chromatography over silica gel (eluent: EtOAc-hexane).
(S)-sec-Butyl (E)-2-benzoylamino-3-(1-naphthyl)-2-propenoate [(E)-1a]: mp 118.5–119.0 °C; IR
(KBr) #/cm–1 = 3454, 1654, 1560; [%]D25 –1.6 (c 0.5, MeOH); H NMR (600 MHz, DMSO-d6) $ = 0.50
1
(3H, t, J =7.6 Hz), 0.83 (3H, d, J = 5.2 Hz), 1.19 (2H, dq, J = 6.3, 7.6 Hz), 4.60 (1H, tq, J = 5.2, 6.3 Hz),
7.27 (1H, s), 7.33 (1H, d, J = 6.9 Hz), 7.47 (1H, dd, J = 7.5, 7.5 Hz), 7.56 (2H, dd, J = 7.5, 8.0 Hz), 7.54–
7.58 (2H, m), 7.63 (1H, dd, J = 6.9, 7.5 Hz), 7.88 (1H, d, J = 7.6 Hz), 7.99 (2H, d, J = 8.0 Hz), 8.00 (1H,
dd, J = 6.9, 6.9 Hz), 8.02 (1H, d. J = 8.0 Hz), 10.6 (1H, s); 13C NMR (150 MHz, DMSO-d6) $ = 8.9, 18.2,

1346
HETEROCYCLES, Vol. 83, No. 6, 2011
27.6, 72.3, 120.0, 122.2, 124.6, 125.3, 125.9, 126.1, 126.3, 127.7 (2C), 127.9, 128.3, 128.5 (2C), 131.2,
131.9, 132.0, 132.1, 133.0, 164.0, 165.0. Anal. Calcd for C24H23NO3: C, 77.19; H, 6.21; N, 3.75. Found:
C, 77.34; H, 6.25; N, 3.61.
(4R,5R)-4-[(S)-sec-Butoxycarbonyl]-5-(1-naphthyl)-2-phenyl-4,5-dihydrooxazole [(4R,5R)-2a]: mp
111.0–111.5 °C; IR (KBr) #/cm–1 = 1734, 1653; [%]D25 –460.7 (c 0.5, MeOH); [!]220 –420 deg cm2 dmol–1
(2.0"10–5 mol dm–3, MeOH); 1H NMR (600 MHz, DMSO-d6) $ = –0.33 (3H, d, J = 6.3 Hz), 0.54 (3H, t, J
= 7.5 Hz), 1.02 (2H, dq, J = 7.5, 7.5 Hz), 4.01 (1H, tq, J = 7.5, 7.5 Hz), 5.57 (1H, d, J = 10.3 Hz), 6.83
(1H, d, J = 10.3 Hz), 7.48 (1H, dd, J = 7.5, 7.5 Hz), 7.51 (1H, d, J = 7.5 Hz), 7.56–7.60 (2H, m), 7.57 (2H,
dd, J = 7.5, 8.0 Hz), 7.65 (1H, dd, J = 7.5, 7.5 Hz), 7.89 (1H, d, J = 7.5 Hz), 7.95 (1H, d, J = 8.0 Hz), 8.06
13
(2H, d, J = 8.0 Hz), 8.10 (1H, d, J = 8.6 Hz); C NMR (150 MHz, DMSO-d6) $ = 8.9, 16.7. 27.6, 71.7,
72.1, 80.2, 123.1, 123.8, 125.1, 125.9, 126.2, 126.8, 128.2 (2C), 128.3, 128.4, 128.9 (2C), 130.1, 132.0,
132.2, 133.0, 165.0, 168.3. Anal. Calcd for C24H23NO3: C, 77.19; H, 6.21; N, 3.75. Found: C, 76.96; H,
5.99; N, 3.67.
(4S,5S)-4-[(S)-sec-Butoxycarbonyl]-5-(1-naphthyl)-2-phenyl-4,5-dihydrooxazole [(4S,5S)-2a]: mp
90.5–91.0 °C; IR (KBr) #/cm–1 = 1734, 1653; [%]D25 +365.5 (c 0.5, MeOH); [!]220 +300 deg cm2 dmol–1
(2.0"10–5 mol dm–3, MeOH); 1H NMR (600 MHz, DMSO-d6) $ = 0.12 (3H, t, J = 7.5 Hz), 0.39 (2H, dq, J
= 7.5, 7.5 Hz), 0.60 (3H, d, J = 6.3 Hz), 3.96 (1H, tq, J = 7.5, 7.5 Hz), 5.53 (1H, d, J = 10.3 Hz), 6.81 (1H,
d, J = 10.3 Hz), 7.50 (1H, dd, J = 7.5, 8.0 Hz), 7.55–7.56 (2H, m), 7.56 (2H, dd, J = 6.9, 7.5 Hz), 7.59
(1H, d, J = 7.5 Hz), 7.65 (1H, dd, J =7.5, 7.5 Hz), 7.89 (1H, d, J = 8.0 Hz), 7.95 (1H, d, J = 8.0 Hz), 8.05
13
(2H, d, J = 6.9 Hz), 8.08 (1H, d, J = 8.6 Hz); C NMR (150 MHz, DMSO-d6) $ = 8.3, 18.1, 26.7, 71.9,
72.6, 80.3, 123.2, 123.6, 125.1, 125.9, 126.3, 126.8, 128.1 (2C), 128.3, 128.4, 128.8 (2C), 129.9, 131.9,
132.2, 133.0, 165.1, 168.1. Anal. Calcd for C24H23NO3: C, 77.19; H, 6.21; N, 3.75. Found: C, 76.87; H,
6.12; N, 3.61.
(4R,5S)-4-[(S)-sec-Butoxycarbonyl]-5-(1-naphthyl)-2-phenyl-4,5-dihydrooxazole [(4R,5S)-2a]: oily
25
liquid; IR (neat) #/cm–1 = 1734, 1653, 1560; [%]D +108.9 (c 0.5, MeOH); [!]220 +150 deg cm2 dmol–1
(2.0"10–5 mol dm–3, MeOH); 1H NMR (600 MHz, DMSO-d6) $ = 0.87 (3H, t, J= 7.5 Hz), 1.28 (3H, d, J
= 6.3 Hz), 1.59 (2H, dq, J = 7.5 Hz), 4.78 (1H, d, J = 6.3 Hz), 4.95 (1H, tq, J = 7.5, 7.5 Hz), 6.66 (1H, d,
J = 6.3 Hz), 7.51 (1H, d, J = 8.0 Hz), 7.54 (1H, dd, J = 7.5, 8.0 Hz), 7.58 (2H, dd, J = 7.5, 7.5 Hz), 7.60–
7.62 (2H, m), 7.67 (1H, dd, J = 6.3, 7.5 Hz), 7.96–7.98 (2H, m), 8.02–8.04 (1H, m), 8.05 (2H, d, J = 7.5
Hz); 13C NMR (150 MHz, DMSO-d6) $ = 9.3, 19.1, 28.1, 73.4, 75.7, 78.5, 80.7, 122.6, 122.9, 125.5,
126.3, 126.4, 126.7, 128.3 (2C), 129.0 (2C), 129.1, 129.2, 132.4, 133.5, 134.6, 164.5, 170.2. HR EI-MS
m/z calcd for C24H23NO3: 373.1678. Found: 373.1678.
(4S,5R)-4-[(S)-sec-Butoxycarbonyl]-5-(1-naphthyl)-2-phenyl-4,5-dihydrooxazole [(4S,5R)-2a]: oily
25
liquid; IR (neat) #/cm–1 = 1734, 1639, 1577; [%]D +73.7 (c 0.5, MeOH); [!]220 –50 deg cm2 dmol–1
(2.0"10–5 mol dm–3, MeOH); 1H NMR (600 MHz, DMSO-d6) $ = 0.88 (3H, t, J = 7.5 Hz), 1.24 (3H, d, J

HETEROCYCLES, Vol. 83, No. 6, 2011
1347
= 6.3 Hz), 1.62 (2H, dq, J = 7.5, 7.5 Hz), 4.76 (1H, d, J = 6.3 Hz), 4.95 (1H, tq, J = 7.5, 7.5 Hz), 6.65 (1H,
d, J = 6.3 Hz), 7.52–7.54 (2H, m), 7.58 (2H, dd, J = 7.5, 7.5 Hz), 7.59–7.61 (2H, m), 7.65 (1H, dd, J = 7.5,
7.5 Hz), 7.92–7.93 (1H, m), 7.97 (1H, d, J = 8.0 Hz), 8.04 (1H, d, J = 7.5 Hz), 8.05 (2H, d, J = 7.5 Hz);
13C NMR (150 MHz, DMSO-d6) $ = 9.4, 19.1, 28.0, 71.9, 73.6, 75.7, 80.8, 122.5, 122.8, 125.5, 126.3,
126.4, 126.7, 128.3 (2C), 129.0 (2C), 129.1, 129.2, 132.4, 133.5, 134.6, 164.6, 170.2. HR EI-MS m/z
calcd for C24H23NO3: 373.1678. Found: 373.1678.
(4R,5R)-5-(1-Naphthyl)-4-[(S)-2-octyloxycarbonyl]-2-phenyl-4,5-dihydrooxazole [(4R,5R)-2b]: oily
liquid; IR (neat) #/cm–1 = 1742, 1655; [%]D25 –370.5 (c 0.5, MeOH); [!]220 –1040 deg cm2 dmol-1 (2.0"10-
mol dm–3, MeOH); H NMR (600 MHz, DMSO-d6) $ = –0.29 (3H, d, J = 6.3 Hz), 0.81 (3H, t, J = 7.5
5
1
Hz), 0.80–1.13 (8H, m), 1.19 (1H, tq, J = 7.5, 7.5 Hz), 4.07 (1H, tq, J = 5.2, 6.3 Hz), 5.56 (1H, d, J = 10.9
Hz), 6.82 (1H, d, J = 10.9 Hz), 7.48 (1H, dd, J = 6.9, 8.0 Hz), 7.52 (1H, d, J = 8.0 Hz), 7.54–7.58 (2H, m),
7.60 (2H, dd, J = 6.9, 7.5 Hz), 7.65 (1H, dd, J = 7.5, 7.5 Hz), 7.88 (1H, d, J = 6.9 Hz), 7.94 (1H, d, J =
13
7.5 Hz), 8.04 (2H, d, J = 6.9 Hz), 8.10 (1H, d, J = 8.6 Hz); C NMR (150 MHz, DMSO-d6) $ = 13.9,
17.3, 21.9, 24.2, 28.3, 31.0, 34.6, 70.6, 72.1, 80.1, 123.1, 123.8, 125.1, 125.9, 126.1, 126.7, 128.2 (2C),
128.3, 128.4, 128.8 (2C), 130.1, 132.0, 132.2, 133.0, 165.0, 168.2. Anal. Calcd for C28H31NO3: C, 78.29;
H, 7.27; N, 3.26. Found: C, 77.88; H, 7.20; N, 3.25.
(4S,5S)-5-(1-Naphthyl)-4-[(S)-2-octyloxycarbonyl]-2-phenyl-4,5-dihydrooxazole [(4S,5S)-2b]: oily
liquid; IR (neat) #/cm–1 = 1742, 1655; [%]D25 +224.2 (c 0.5, MeOH); [!]220 +850 deg cm2 dmol-1 (2.0"10-5
mol dm–3, MeOH); 1H NMR (600 MHz, DMSO-d6) $ = 0.53 (2H, m), 0.78 (3H, d, J = 6.3 Hz), 0.76–0.96
(8H, m), 0.84 (3H, t, J = 6.3 Hz), 4.00 (1H, tq, J = 6.3, 6.3 Hz), 5.53 (1H, d, J = 10.3 Hz), 6.80 (1H, d, J =
10.3 Hz), 7.49 (1H, dd, J = 7.5, 7.5 Hz), 7.53–7.58 (3H, m), 7.57 (2H, dd, J = 7.5, 8.0 Hz), 7.65 (1H, dd,
J = 8.0, 8.0 Hz), 7.88 (1H, d, J = 8.0 Hz), 7.93 (1H, d, J = 7.5 Hz), 8.05 (2H, d, J = 8.0 Hz), 8.08 (1H, d, J
13
= 8.0 Hz); C NMR (150 MHz, DMSO-d6) $ = 14.0, 18.7, 22.0, 23.8, 28.2, 30.8, 33.8, 71.0, 72.6, 80.4,
123.3, 123.7, 125.2, 125.9, 127.3, 126.3, 126.8, 128.2 (2C), 128.4, 128.9 (2C), 130.0, 132.0, 132.3, 133.0,
165.0, 168.2. Anal. Calcd for C28H31NO3: C, 78.29; H, 7.27; N, 3.26. Found: C, 77.96; H, 7.30; N, 3.25.
(4R,5S)-5-(1-Naphthyl)-4-[(S)-2-octyloxycarbonyl]-2-phenyl-4,5-dihydrooxazole [(4R,5S)-2b]: oily
25
1
liquid; [%]D +98.4 (c 0.5, MeOH); [!]220 +720 deg cm2 dmol-1 (2.0"10-5 mol dm–3, MeOH); H NMR
(600 MHz, DMSO-d6) $ = 0.79 (3H, t, J = 6.9 Hz), 1.18–1.28 (8H, m), 1.27 (3H, d, J = 6.3 Hz), 1.52–
1.57 (2H, m), 4.76 (1H, d, J = 6.3 Hz), 5.01 (1H, tq, J = 6.3, 6.3 Hz), 6.65 (1H, d, J = 6.3 Hz), 7.49 (1H,
dd, J = 7.5, 7.5 Hz), 7.54 (1H, dd, J = 7.5, 7.5 Hz), 7.56 (2H, dd, J = 6.9, 7.5 Hz), 7.58–7.60 (2H, m),
7.65 (1H, dd, J = 8.0, 8.0 Hz), 7.94–7.98 (2H, m), 8.02 (1H, d, J = 8.0 Hz), 8.03 (2H, d, J = 6.9 Hz); 13C
NMR (150 MHz, DMSO-d6) $ = 14.6, 20.4, 22.6, 25.3, 29.1, 31.9, 35.9, 73.0, 76.4, 81.3, 123.3, 123.6,
126.3, 126.9, 127.1, 127.4, 129.0 (2C), 129.66 (2C), 129.72, 129.8, 129.9, 133.2, 134.3, 135.3, 165.2,
170.9. HR FAB-MS m/z calcd for C28H32NO3: 430.2382 [M + H]+. Found: 430.2384.
(4S,5R)-5-(1-Naphthyl)-4-[(S)-2-octyloxycarbonyl]-2-phenyl-4,5-dihydrooxazole [(4S,5R)-2b]: oily

1348
HETEROCYCLES, Vol. 83, No. 6, 2011
25
1
liquid; [%]D –23.2 (c 0.5, MeOH); [!]220 –860 deg cm2 dmol-1 (2.0"10-5 mol dm–3, MeOH); H NMR
(600 MHz, DMSO-d6) $ = 0.80 (3H, t, J = 6.9 Hz), 1.01 (3H, d, J = 6.3 Hz), 1.17–1.27 (8H, m), 1.52–
1.59 (2H, m), 4.75 (1H, d, J = 6.3 Hz), 4.98 (1H, tq, J = 6.3, 6.3 Hz), 6.62 (1H, d, J = 6.3 Hz), 7.51 (1H,
dd, J = 7.5, 7.5 Hz), 7.53–7.60 (3H, m), 7.56 (2H, dd, J = 7.5, 7.5 Hz), 7.65 (1H, dd, J = 8.0, 8.0 Hz),
7.91 (1H, d, J = 8.0 Hz), 7.96 (1H, d, J = 7.5 Hz), 8.02 (1H, d, J = 8.0 Hz), 8.04 (2H, d, J = 7.5 Hz); 13C
NMR (150 MHz, DMSO-d6) $ = 13.9, 19.6, 21.9, 22.5, 24.6, 28.4, 31.1, 35.1, 39.1, 72.4, 75.7, 80.7,
122.5, 122.9, 125.5, 126.1, 126.3, 126.7, 128.3 (2C), 128.7, 128.9, 129.0, 129.1, 132.4, 133.5, 164.5,
170.1. HR FAB-MS m/z calcd for C28H32NO3: 430.2382 [M + H]+. Found: 430.2384.
(4R,5R)-4-[(1R,2S,5R)-(–)-Menthyloxycarbonyl]-5-(1-naphthyl)-2-phenyl-4,5-dihydrooxazole
25
[(4R,5R)-2c]: oily liquid; IR (neat) #/cm–1 = 1734, 1654; [%]D –193.8 (c 0.5, MeOH); [!]220 –1020 deg
1
cm2 dmol-1 (2.0"10-5 mol dm–3, MeOH); H NMR (600 MHz, DMSO-d6) $ = 0.01 (3H, d, J = 6.9 Hz),
0.35 (3H, d, J = 6.9 Hz), 0.67 (3H, d, J = 6.9 Hz), 0.35–1.59 (9H, m), 3.95 (1H, ddd, J = 6.9, 6.9, 6.9 Hz),
5.54 (1H, d, J = 10.3 Hz), 6.77 (1H, d, J = 10.3 Hz), 7.43 (1H, dd, J = 8.0, 8.0 Hz), 7.47 (1H, d, J = 8.0
Hz), 7.56–7.61 (4H, m), 7.65 (1H, dd, J = 7.5, 7.5 Hz), 7.76 (1H, d, J = 8.0 Hz), 7.89 (1H, d, J = 8.0 Hz),
7.95 (1H, d, J = 8.0 Hz), 8.04 (2H, d, J = 7.5 Hz); 13C NMR (150 MHz, DMSO-d6) $ = 15.4, 20.2, 20.5,
21.8, 22.4, 24.6, 30.6, 45.5, 72.8, 80.5, 123.3, 123.5, 125.1, 125.8, 126.3, 126.7, 127.2, 127.4, 128.1 (2C),
128.2, 128.4, 128.5, 128.8 (2C), 129.6, 131.6, 132.2, 165.2, 168.1. Anal. Calcd for C30H33NO3: C, 79.09;
H, 7.30; N, 3.07. Found: C, 78.81; H, 6.91; N, 3.33.
(4S,5S)-4-[(1R,2S,5R)-(–)-Menthyloxycarbonyl]-5-(1-naphthyl)-2-phenyl-4,5-dihydrooxazole
25
[(4S,5S)-2c]: oily liquid; IR (neat) #/cm–1 = 1739, 1653; [%]D +173.7 (c 0.5, MeOH); [!]220 +1090 deg
1
cm2 dmol-1 (2.0"10-5 mol dm–3, MeOH); H NMR (600 MHz, DMSO-d6) $ = –0.30 (1H, m), 0.27–0.29
(1H, m), 0.42 (3H, d, J = 6.3 Hz), 0.54 (3H, d, J = 6.9 Hz), 0.68–0.84 (7H, m), 0.73 (3H, d, J = 6.9 Hz),
3.96 (1H, ddd, J = 6.3, 6.3, 6.3 Hz), 5.58 (1H, d, J = 10.9 Hz), 6.83 (1H, d, J = 10.9 Hz), 7.49–7.61 (6H,
m), 7.66 (1H, dd, J = 6.9, 6.9 Hz), 7.88–7.90 (1H, m), 7.94 (1H, d, J = 8.0 Hz), 8.05 (2H, d, J = 6.9 Hz),
13
8.10 (1H, d, J = 8.0 Hz); C NMR (150 MHz, DMSO-d6) $ = 16.3, 20.6, 21.6, 25.8, 30.2, 33.5, 37.9,
46.1, 72.3, 80.4, 123.6, 124.1, 125.5, 126.1, 126.5, 127.0, 127.6, 128.5 (2C), 128.7, 128.8, 129.1 (2C),
130.7, 131.5, 132.2, 132.5, 133.6, 165.4, 168.5. Anal. Calcd for C30H33NO3: C, 79.09; H, 7.30; N, 3.07.
Found: C, 78.80; H, 6.96; N, 2.95.
(4R,5S)-4-[(1R,2S,5R)-(–)-Menthyloxycarbonyl]-5-(1-naphthyl)-2-phenyl-4,5-dihydrooxazole
25
[(4R,5S)-2c]: oily liquid; [%]D +48.9 (c 0.5, MeOH); [!]220 +900 deg cm2 dmol-1 (2.0"10-5 mol dm–3,
MeOH); 1H NMR (600 MHz, DMSO-d6) $ = 0.76 (3H, d, J = 6.9 Hz), 0.78 (3H, d, J = 6.9 Hz), 0.89 (3H,
d, J = 6.9 Hz), 1.06–1.10 (2H, m), 1.35–1.40 (2H, m), 1.46–1.48 (1H, m), 1.60–1.63 (2H, m), 1.78–1.80
(1H, m), 1.95–1.98 (1H, m), 4.74 (1H, d, J = 6.9 Hz), 4.76 (1H, ddd, J = 4.8, 4.8, 5.5 Hz), 6.61 (1H, d, J
= 6.9 Hz), 7.51 (1H, d, J = 7.5 Hz), 7.53 (1H, dd, J = 7.5, 7.5 Hz), 7.53–7.56 (1H, m), 7.56 (2H, dd, J =
7.5, 7.5 Hz), 7.60 (1H, dd, J = 7.5, 7.5 Hz), 7.65 (1H, dd, J = 7.5, 7.5 Hz), 7.82 (1H, d, J = 7.5 Hz), 7.97
13
(1H, d, J = 7.5 Hz), 8.03 (1H, d, J = 8.3 Hz), 8.04 (2H, d, J = 7.5 Hz); C NMR (150 MHz, DMSO-d6)

HETEROCYCLES, Vol. 83, No. 6, 2011
1349
$ = 16.3 (2C), 20.5 (2C), 21.9, 23.0, 25.9, 30.9, 33.6, 40.3, 46.4, 64.4, 75.4, 76.6, 82.3, 109.0, 110.2,
118.1, 125.7, 126.4 (2C), 126.8, 128.4, 129.1 (2C), 129.2, 133.7, 134.4, 165.2, 170.2. HR FAB-MS m/z
calcd for C30H34NO3: 456.2539 [M + H]+. Found: 456.2538.
(4S,5R)-4-[(1R,2S,5R)-(–)-Menthyloxycarbonyl]-5-(1-naphthyl)-2-phenyl-4,5-dihydrooxazole
25
[(4S,5R)-2c]: oily liquid; [%]D –199.6 (c 0.5, MeOH); [!]220 –910 deg cm2 dmol-1 (2.0"10-5 mol dm–3,
MeOH); 1H NMR (600 MHz, DMSO-d6) $ = 0.72 (3H, d, J = 6.9 Hz), 0.83 (3H, d, J = 6.9 Hz), 0.86–0.87
(1H, m), 0.92 (3H, d, J = 6.9 Hz), 1.05–1.08 (2H, m), 1.37–1.39 (1H, m), 1.50–1.52 (1H, m), 1.63–1.67
(2H, m), 1.88–1.89 (1H, m), 2.07–2.09 (1H, m), 4.77 (1H, ddd, J = 4.1, 4.5, 5.5 Hz), 4.78 (1H, d, J = 6.9
Hz), 6.64 (1H, d, J = 6.9 Hz), 7.49 (1H, d, J = 7.5 Hz), 7.53 (1H, dd, J = 7.5, 7.5 Hz), 7.57 (2H, dd, J =
7.5, 7.5 Hz), 7.59–7.61 (2H, m), 7.65 (1H, dd, J = 7.5, 7.5 Hz), 7.94 (1H, d, J = 8.0 Hz), 7.98 (1H, d, J =
7.5 Hz), 8.02 (1H, d, J = 8.0 Hz), 8.04 (2H, d, J = 7.5 Hz); 13C NMR (150 MHz, DMSO-d6) $ = 16.6 (2C),
20.6 (2C), 22.1, 23.4, 26.1, 31.1, 33.8, 40.5, 46.7, 75.6, 76.0, 81.0, 122.8, 123.1, 125.9, 126.5, 127.0,
128.5, 129.3 (2C), 129.36, 129.39 (2C), 132.8, 133.8 (2C), 164.9, 170.4. HR FAB-MS m/z calcd for
C30H34NO3: 456.2539 [M + H]+. Found: 456.2548.
(4R,5R)-5-(1-Naphthyl)-2-phenyl-4-[(1R,2S,5R)-(–)-8-phenylmenthyloxycarbonyl]-4,5-dihydro-
25
oxazole [(4R,5R)-2d]: oily liquid; [%]D –115.2 (c 0.1, MeOH); [!]220 –230 deg cm2 dmol-1 (2.0"10-5
1
mol dm–3, MeOH); H NMR (600 MHz, DMSO-d6) $ = – 0.37–0.34 (1H, m), 0.35–0.37 (1H, m), 0.43
(3H, d, J = 6.3 Hz), 0.70–0.82 (3H, m), 1.00 (3H, s), 1.08 (3H, s), 1.22–1.30 (3H, m), 3.86 (1H, ddd, J =
4.1, 5.0, 5.0 Hz), 5.62 (1H, d, J = 10.3 Hz), 6.84 (1H, d, J = 10.3 Hz), 7.08 (1H, dd, J = 7.5, 7.5 Hz), 7.10
(2H, d, J = 7.5 Hz), 7.18 (2H, dd, J = 7.5, 7.5 Hz), 7.52–7.58 (3H, m), 7.57 (2H, dd, J = 7.5, 8.0 Hz), 7.63
(1H, d, J = 7.5 Hz), 7.65 (1H, dd, J = 7.5, 7.5 Hz), 7.89 (1H, d, J = 8.0 Hz), 7.92 (1H, d, J = 7.5 Hz), 8.00
(1H, d, J = 8.0 Hz), 8.07 (2H, d, J = 8.0 Hz); 13C NMR (150 MHz, DMSO-d6) $ = 21.3, 26.8, 27.5, 30.3,
31.4, 33.8, 41.6, 49.9, 50.2, 57.0, 80.8, 91.9, 93.0, 98.9, 99.3, 120.2, 123.6, 124.3, 125.5 (2C), 125.9 (2C),
126.1, 127.9, 129.0 (2C), 130.1 (2C), 132.9, 133.9, 135.6, 140.6, 147.2, 159.6, 160.0, 163.9. Anal. Calcd
for C36H37NO3: C, 81.32; H, 7.01; N, 2.63. Found: C, 81.02; H, 7.30; N, 2.28.
(4S,5S)-5-(1-Naphthyl)-2-phenyl-4-[(1R,2S,5R)-(–)-8-phenylmenthyloxycarbonyl]-4,5-dihydro-
25
oxazole [(4S,5S)-2d]: oily liquid; [%]D +294.4 (c 0.1, MeOH); [!]220 +840 deg cm2 dmol-1 (2.0"10-5
1
mol dm–3, MeOH); H NMR (600 MHz, DMSO-d6) $ = – 0.42–0.40 (1H, m), 0.19–0.20 (1H, m), 0.36
(3H, d, J = 6.3 Hz), 0.70–0.80 (3H, m), 1.03 (3H, s), 1.13 (3H, s), 1.22–1.30 (3H, m), 4.02 (1H, ddd, J =
4.1, 5.0, 5.0 Hz), 4.69 (1H, d, J = 10.3 Hz), 6.60 (1H, d, J = 10.3 Hz), 7.19 (2H, d, J = 7.5 Hz), 7.20 (1H,
dd, J = 7.5, 7.5 Hz), 7.35 (2H, dd, J = 7.5, 7.5 Hz), 7.40 (1H, d, J = 7.5 Hz), 7.45 (1H, dd, J = 7.5, 7.5 Hz),
7.55 (2H, dd, J = 7.5, 7.5 Hz), 7.59 (1H, dd, J = 7.5, 7.5 Hz), 7.60–7.67 (2H, m), 7.79 (1H, d, J = 8.0 Hz),
7.85 (1H, d, J = 7.5 Hz), 7.92 (1H, d, J = 8.0 Hz), 8.03 (2H, d, J = 7.5 Hz); 13C NMR (150 MHz, DMSO-
d6) $ = 21.4, 25.3, 25.8, 27.5, 30.1, 33.9, 38.3, 49.6, 72.0, 74.1, 80.0, 123.5, 124.2, 125.36, 125.40, 125.5
(2C), 126.2, 126.5, 126.8, 128.2 (2C), 128.5 (2C), 128.7, 128.9, 129.2 (2C), 130.7, 132.2, 132.6, 133.6,
135.2, 152.3, 165.3, 168.0. Anal. Calcd for C36H37NO3: C, 81.32; H, 7.01; N, 2.63. Found: C, 81.59; H,

1350
HETEROCYCLES, Vol. 83, No. 6, 2011
7.40; N, 2.33.
(4R,5S)-5-(1-Naphthyl)-2-phenyl-4-[(1R,2S,5R)-(–)-8-phenylmenthyloxycarbonyl]-4,5-dihydro-
oxazole [(4R,5S)-2d]: oily liquid; [%]D25 +31.8 (c 0.5, MeOH); [!]220 +320 deg cm2 dmol-1 (2.0"10-5 mol
dm–3, MeOH); 1H NMR (600 MHz, DMSO-d6) $ = 0.86 (3H, d, J = 6.3 Hz), 0.89–0.90 (1H, m), 1.07 (3H,
s), 1.11 (3H, s), 1.03–1.17 (2H, m), 1.45–1.48 (1H, m), 1.61–1.63 (1H, m), 1.67–1.70 (1H, m), 1.79–1.80
(1H, m), 2.08–2.11 (1H, m), 3.78 (1H, d, J = 7.6 Hz), 4.79 (1H, ddd, J = 6.9, 6.9, 6.9 Hz), 6.41–6.45 (3H,
m), 6.48 (1H, d, J = 7.6 Hz), 6.91–6.95 (2H, m), 7.46 (1H, d, J = 7.6 Hz), 7.52 (2H, dd, J = 7.6, 8.0 Hz),
7.54 (1H, dd, J = 7.6, 7.6 Hz), 7.60 (1H, dd, J = 7.6, 7.6 Hz), 7.62–7.67 (2H, m), 7.76–7.78 (1H, m), 7.95
13
(2H, d, J = 8.0 Hz), 8.03 (1H, d, J = 7.6 Hz), 8.09–8.10 (1H, m); C NMR (150 MHz, DMSO-d6) $ =
21.6, 23.8, 25.9, 28.5, 30.7, 33.9, 39.1, 40.7, 49.3, 75.6, 75.7, 79.2, 80.2, 122.6, 123.5, 124.3, 124.9 (2C),
125.6, 126.24, 126.27, 126.8, 127.3 (2C), 128.2 (2C), 128.9 (2C), 129.1, 129.5, 132.4, 133.6, 134.4,
151.1, 164.0, 169.1. HR FAB-MS m/z calcd for C36H38NO3: 532.2852 [M + H]+. Found: 532.2847.
(4S,5R)-5-(1-Naphthyl)-2-phenyl-4-[(1R,2S,5R)-(–)-8-phenylmenthyloxycarbonyl]-4,5-dihydro-
oxazole [(4S,5R)-2d]: oily liquid; [%]D25 –18.7 (c 0.5, MeOH); [!]220 –280 deg cm2 dmol-1 (2.0"10-5 mol
1
dm–3, MeOH); H NMR (600 MHz, DMSO-d6) $ = 0.83–0.85 (1H, m), 0.88 (3H, d, J = 6.2 Hz), 1.04–
1.08 (2H, m), 1.17 (3H, s), 1.22 (3H, s), 1.48–1.50 (1H, m), 1.92–1.95 (1H, m), 1.97–2.02 (3H, m), 4.22
(1H, d, J = 6.2 Hz), 4.73 (1H, ddd, J = 6.8, 6.8, 6.8 Hz), 6.39 (1H, d, J = 6.2 Hz), 6.79 (1H, dd, J = 7.5,
7.5 Hz), 6.95 (2H, dd, J = 7.5, 7.5 Hz), 7.15 (2H, dd, J = 7.5, 7.5 Hz), 7.38 (1H, d, J = 7.5 Hz), 7.53 (1H,
dd, J = 7.5, 7.5 Hz), 7.56 (2H, dd, J = 7.5, 7.5 Hz), 7.61–7.63 (3H, m), 7.88 (1H, d, J = 8.3 Hz), 7.97 (1H,
13
d, J = 7.5 Hz), 8.02 (2H, d, J = 6.9 Hz), 8.04 (1H, d, J = 8.3 Hz); C NMR (150 MHz, DMSO-d6) $ =
22.4, 27.0, 27.3, 27.5, 31.5, 34.6, 41.8, 50.4, 75.9, 76.3, 81.4, 123.6, 124.3, 125.5, 126.0 (2C), 126.2,
126.9, 127.1, 127.3, 128.3 (2C), 128.5, 129.0 (2C), 129.66 (2C), 129.69, 129.8, 130.0, 133.1, 134.3,
135.2, 150.9, 165.1, 170.4. HR FAB-MS m/z calcd for C36H38NO3: 532.2852 [M + H]+. Found: 532.2849.
cis-4-tert-Butoxycarbonyl-5-(1-naphthyl)-2-phenyl-4,5-dihydrooxazole (cis-2e): mp 144.0–145.0 °C;
1
IR (KBr) #/cm–1 = 1737, 1649; H NMR (500 MHz, DMSO-d6) $ = 0.50 (9H, s), 5.48 (1H, d, J = 10.3
Hz), 6.81 (1H, d, J = 10.3 Hz), 7.51 (1H, d, J = 8.2 Hz), 7.54 (1H, dd, J = 7.6, 8.2 Hz), 7.58 (1H, dd, J =
7.6, 7.6 Hz), 7.58 (2H, dd, J = 6.9, 7.6 Hz), 7.62 (1H, dd, J = 7.6, 8.2 Hz), 7.66 (1H, dd, J = 7.6, 7.6 Hz),
7.93 (1H, d, J = 7.6 Hz), 7.98 (1H, d, J = 7.6 Hz), 8.07 (2H, d, J = 6.9 Hz), 8.11 (1H, d, J = 8.2 Hz); 13C
NMR (125 MHz, DMSO-d6) $ = 26.4 (3C), 72.5, 80.0, 80.2, 123.1, 124.0, 125.2, 125.9, 126.1, 126.8,
128.1 (2C), 128.31, 128.33, 128.8 (2C), 130.2, 132.1, 132.3, 133.0, 164.8, 167.6. Anal. Calcd for
C24H23NO3: C, 77.19; H, 6.21; N, 3.75. Found: C, 77.30; H, 6.03; N, 3.65.
trans-4-tert-Butoxycarbonyl-5-(1-naphthyl)-2-phenyl-4,5-dihydrooxazole (trans-2e): oily liquid; IR
1
(neat) #/cm–1 = 1728, 1647; H NMR (500 MHz, DMSO-d6) $ = 1.51 (9H, s), 4.65 (1H, d, J = 6.2 Hz),
6.61 (1H, d, J = 6.2 Hz), 7.50 (1H, d, J = 6.9 Hz), 7.54 (1H, dd, J = 6.9, 6.9 Hz), 7.58 (2H, dd, J = 7.6,
7.6 Hz), 7.60–7.63 (2H, m), 7.67 (1H, dd, J = 7.6, 7.6 Hz), 7.97 (1H, d, J = 6.9 Hz), 7.97 (1H, d, J = 6.9

HETEROCYCLES, Vol. 83, No. 6, 2011
1351
13
Hz), 8.03–8.06 (1H, m), 8.06 (2H, d, J = 7.6 Hz); C NMR (125 MHz, DMSO-d6) $ = 27.6 (3C), 76.4,
80.8, 82.1, 122.7, 122.8, 125.5, 126.2, 126.4, 126.6, 128.3 (2C), 128.92, 128.94 (2C), 129.0, 129.1, 132.4,
133.5, 134.7, 164.4, 169.6. Anal. Calcd for C24H23NO3: C, 77.19; H, 6.21; N, 3.75. Found: C, 76.94; H,
5.96; N, 3.57.
cis-4-Methoxycarbonyl-5-(1-naphthyl)-2-phenyl-4,5-dihydrooxazole (cis-2f): mp 133.0–134.0 °C; IR
(KBr) #/cm–1 = 1742, 1646; 1H NMR (500 MHz, DMSO-d6) $ = 2.72 (3H, s), 5.62 (1H, d, J = 10.3 Hz),
6.88 (1H, d, J = 10.3 Hz), 7.51–7.52 (2H, m), 7.57 (1H, dd, J = 7.4, 7.4 Hz), 7.59 (2H, dd, J = 7.4, 7.7
Hz), 7.60 (1H, dd, J = 7.4, 8.7 Hz), 7.67 (1H, dd, J = 7.4, 7.4 Hz), 7.90–7.92 (1H, m), 7.96 (1H, d, J = 7.4
13
Hz), 8.08 (2H, d, J = 7.7 Hz), 8.10 (1H, d, J = 8.7 Hz); C NMR (125 MHz, DMSO-d6) $ = 50.7, 72.7,
80.0, 122.9, 123.6, 125.1, 125.9, 126.2, 126.4, 128.2 (2C), 128.3, 128.4, 128.9 (2C), 129.7, 132.0, 132.3,
132.8, 165.2, 169.0. Anal. Calcd for C21H17NO3: C, 76.12; H, 5.17; N, 4.23. Found: C, 75.89; H, 5.20; N,
4.48.
trans-4-Methoxycarbonyl-5-(1-naphthyl)-2-phenyl-4,5-dihydrooxazole (trans-2f): mp 108.0–109.0
°C; IR (KBr) #/cm–1 = 1742, 1640; 1H NMR (500 MHz, DMSO-d6) $ = 3.81 (3H, s), 4.89 (1H, d, J = 6.9
Hz), 6.70 (1H, d, J = 6.9 Hz), 7.52 (1H, d, J = 7.4 Hz), 7.54 (1H, dd, J = 6.9, 7.4 Hz), 7.57 (2H, dd, J =
7.4, 7.4 Hz), 7.62 (1H, dd, J = 8.6, 9.2 Hz), 7.62 (1H, dd, J = 6.3, 9.2 Hz), 7.67 (1H, dd, J = 7.4, 7.4 Hz),
7.98 (1H, d, J = 6.9 Hz), 8.00 (1H, d, J = 8.6 Hz), 8.04 (1H, d, J = 6.3 Hz), 8.05 (2H, d, J = 7.4 Hz); 13C
NMR (125 MHz, DMSO-d6) $ = 53.3, 75.8, 81.2, 123.3, 123.7, 126.1, 126.8, 126.9, 127.4, 128.9 (2C),
129.5 (2C), 129.6, 129.7, 130.0, 133.0, 134.1, 135.0, 165.1, 171.5. Anal. Calcd for C21H17NO3: C, 76.12;
H, 5.17; N, 4.23. Found: C, 76.14; H, 5.21; N, 4.09.
cis-4-tert-Butoxycarbonyl-5-(2-naphthyl)-2-phenyl-4,5-dihydrooxazole (cis-2g): mp 142.0–143.0 °C;
1
IR (KBr) #/cm–1 = 1736, 1655; H NMR (500 MHz, DMSO-d6) $ = 0.77 (9H, s), 5.29 (1H, d, J = 11.0
Hz), 6.24 (1H, d, J = 11.0 Hz), 7.38 (1H, d, J = 8.2 Hz), 7.50–7.53 (2H, m), 7.55 (2H, dd, J = 7.6, 7.6 Hz),
7.64 (1H, dd, J = 7.6, 7.6 Hz), 7.87 (1H, s), 7.89–7.93 (3H, m), 8.02 (2H, d, J = 7.6 Hz); 13C NMR (125
MHz, DMSO-d6) $ = 26.8 (3C), 73.3, 80.4, 82.4, 124.4, 125.7, 126.3, 126.5, 126.8, 127.5, 127.7, 127.8,
128.2 (2C), 128.8 (2C), 132.1, 132.4, 132.8, 133.9, 164.7, 167.7. Anal. Calcd for C24H23NO3: C, 77.19; H,
6.21; N, 3.75. Found: C, 76.83; H, 6.40; N, 3.76.
trans-4-tert-Butoxycarbonyl-5-(2-naphthyl)-2-phenyl-4,5-dihydrooxazole (trans-2g): mp 103.0–104.0
°C; IR (KBr) #/cm–1 = 1730, 1638; 1H NMR (500 MHz, DMSO-d6) $ = 1.47 (9H, s), 4.77 (1H, d, J = 7.6
Hz), 5.97 (1H, d, J = 7.6 Hz), 7.47 (1H, d, J = 8.2 Hz), 7.52–7.55 (4H, m), 7.62 (1H, dd, J = 7.6, 7.6 Hz),
7.92–8.01 (6H, m); 13C NMR (125 MHz, DMSO-d6) $ = 27.6 (3C), 76.7, 81.7, 83.2, 123.3, 125.0, 126.57
(2C), 126.64, 127.6, 128.0, 128.2 (2C), 128.8 (2C), 128.9, 132.2, 132.6, 132.8, 136.8, 164.0, 169.5. Anal.
Calcd for C24H23NO3: C, 77.19; H, 6.21; N, 3.75. Found: C, 77.19; H, 6.43; N, 3.87.
cis-4-tert-Butoxycarbonyl-2,5-diphenyl-4,5-dihydrooxazole (cis-2h): mp 108.0–109.0 °C; IR (KBr)

1352
HETEROCYCLES, Vol. 83, No. 6, 2011
1
#/cm–1 = 1748, 1653; H NMR (500 MHz, DMSO-d6) $ = 0.95 (9H, s), 5.22 (1H, d, J = 10.9 Hz), 6.06
(1H, d, J = 10.9 Hz), 7.29 (2H, d, J = 6.9 Hz), 7.33 (1H, dd, J = 6.9, 6.9 Hz), 7.38 (2H, dd, J = 6.9, 6.9
Hz), 7.54 (2H, dd, J = 7.4, 7.4 Hz), 7.63 (1H, dd, J = 7.4, 7.4 Hz), 7.98 (2H, d, J= 7.4 Hz); 13C NMR (125
MHz, DMSO-d6) $ = 26.9 (3C), 73.1, 80.4, 82.2, 126.7 (2C), 126.8, 128.07 (2C), 128.10 (2C), 128.3,
128.8 (2C), 132.1, 136.5, 164.6, 167.6. Anal. Calcd for C20H21NO3: C, 74.28; H, 6.55; N, 4.33. Found: C,
73.94; H, 6.21; N, 4.39.
trans-4-tert-Butoxycarbonyl-2,5-diphenyl-4,5-dihydrooxazole (trans-2h): mp 89.0–90.0 °C; IR (KBr)
#/cm–1 = 1734, 1643; 1H NMR (500 MHz, DMSO-d6) $ = 1.47 (9H, s), 4.66 (1H, d, J = 7.4 Hz), 5.88 (1H,
d, J = 7.4 Hz), 7.38-7.40 (3H, m), 7.44 (2H, dd, J = 6.9, 7.6 Hz), 7.53 (2H, dd, J = 7.4, 7.4 Hz), 7.62 (1H,
dd, J = 7.4, 7.4 Hz), 7.97 (2H, d, J = 7.4 Hz); 13C NMR (125 MHz, DMSO-d6) $ = 27.6 (3C), 76.8, 81.7,
82.9, 125.7 (2C), 126.5, 128.2 (2C), 128.6, 128.8 (2C), 128.9 (2C), 132.2, 139.6, 164.0, 169.4. Anal.
Calcd for C20H21NO3: C, 74.28; H, 6.55; N, 4.33. Found: C, 74.23; H, 6.25; N, 4.46.
X-Ray crystallographic analysis of (4S,5S)-2e
A colourless prism (of the molecular formula C24H23NO3) having approximate dimensions of
0.35"0.15"0.10 mm was mounted on a glass fiber in a random orientation. Preliminary examination
and data collection were performed with Mo K% radiation (&= 0.71069 Å) on a Rigaku RAXIS-RAPID
equipped with an imaging plate. Data collection and cell refinement: MSC/AFC diffractometer control.
Data reduction: ‘teXsan for windows version 1.06’;10 ‘Structure solution, SIR92’;11
‘Refinement, SHELXL97’.12
Crystal data for (4S,5S)-2e: C24H23NO3, fw = 373.45; orthorhombic, space group P212121 (#19); a =
8.239(3) Å, b = 10.024(4) Å, c = 24.467(9) Å, V = 2020.6(12) Å3; Z = 4; Dcalc = 1.228 g cm–3; R = 0.0634,
wR2 = 0.0582. Crystallographic data (excluding these structure factors) for (4S,5S)-2e have been
deposited with the Cambridge Crystallographic Data Centre as supplementary publication number CCDC
636944. Copies of the data can be obtained, free of charge, on application to CCDC, 12 Union Road,
Cambridge CB2 1EZ, UK (fax: +44(0)-1223-336033 or e-mail: deposit@ccdc.cam.ac.uk).
ACKNOWLEDGMENTS
This research was supported by a “Scientific Frontier Research Project” from the Ministry of
Education, Sports, Culture, Science and Technology, Japan.
REFERENCES
1. a) ‘Synthetic Organic Photochemistry’, ed. by W. M. Horspool, Plenum, New York, 1984; b)
‘Handbook of Photochemistry and Photobiology’, Vol. 2, ed. by H. S. Nalwa, American Scientific
Publishers, Stevenson Ranch, 2003; c) ‘Synthetic Organic Photochemistry’, ed. by A. G.
Griesbeck and J. Mattay, Marcel Dekker, New York, 2005.
2. a) S. Kohmoto, Y. Miyaji, M. Tsuruoka, K. Kishikawa, M. Yamamoto, and K. Yamada, J.

HETEROCYCLES, Vol. 83, No. 6, 2011
1353
Chem. Soc., Perkin Trans. 1, 2001, 2082; b) P. Formentin, M. J. Sabater, M. N. Chretien, H. Garcia,
and J. C. Scaiano, J. Chem. Soc., Perkin Trans. 2, 2002, 164; c) S. C. Shim, D. S. Kim, D. J. Yoo, T.
Wada, and Y. Inoue, J. Org. Chem., 2002, 67, 5718; d) A. Bauer, F. Westkämper, S. Grimme, and T.
Bach, Nature, 2005, 436, 1139.
3. a) A. Joy, J. R. Scheffer, and V. Ramamurthy, Org. Lett., 2000, 2, 119; b) J. R. Scheffer, Can. J.
Chem., 2001, 79, 349; c) L. S. Kaanumalle, J. Sivaguru, N. Arunkumar, S. Karthikeyan, and V.
Ramamurthy, Chem. Commun., 2003, 116.
4. a) A. G. Griesbeck, W. Kramer, and J. Lex, Angew. Chem. Int. Ed., 2001, 40, 577; b) S. Jones and J.
C. C. Atherton, Tetrahedron:Asymmetry, 2001, 12, 1117; c) T. Bach, H. Bergmann, B. Grosch, and
K. Harms, J. Am. Chem. Soc., 2002, 124, 7982; d) K. C. W. Chong, J. Sivaguru, T. Shichi, Y.
Yoshimi, V. Ramamurthy, and J. R. Scheffer, J. Am. Chem. Soc., 2002, 124, 2858.
5. a) A. G. Griesbeck and U. J. Meierhenrich, Angew. Chem. Int. Ed., 2002, 41, 3147; b) ‘Chiral
Photochemistry’, ed. by Y. Inoue and V. Ramamurthy, Marcel Dekker, New York, 2004; c) C.
Müller and T. Bach, Aust. J. Chem., 2008, 61, 557; d) N. Hoffmann, Chem. Rev., 2008, 108, 1052.
6. a) F. D. Lewis, G. D. Reddy, D. M. Bassani, S. Schneider, and M. Gahr, J. Am. Chem. Soc., 1994,
116, 597; b) F. D. Lewis, D. M. Bassani, E. L. Burch, B. E. Cohen, J. A. Engleman, G. D.
Reddy, S. Schneider, W. Jaeger, P. Gedeck, and M. Gahr, J. Am. Chem. Soc., 1995, 117, 660; c) K.
Maekawa, T. Igarashi, K. Kubo, and T. Sakurai, Tetrahedron, 2001, 57, 5515; d) K. Maekawa,
A. Shinozuka, M. Naito, T. Igarashi, and T. Sakurai, Tetrahedron, 2004, 60, 10293.
7. a) K. Maekawa, K. Kubo, T. Igarashi, and T. Sakurai, Tetrahedron, 2004, 60, 1183; b) K. Maekawa,
K. Kubo, T. Igarashi, and T. Sakurai, Tetrahedron, 2005, 61, 11211.
8. K. Maekawa, N. Hishikawa, K. Kubo, T. Igarashi, and T. Sakurai, Tetrahedron, 2007, 63, 11267.
9. J. A. Riddick, W. B. Bunger, and T. K. Sakano, ‘Organic Solvents’, 4th ed., Wiley, Chichester, 1986.
10. Molecular Structure Corporation, ‘teXan for Windows. Single Crystal Structure Analysis Software’,
Ver. 1.06, The Woodlands, Texas, 1999.
11. A. Altomare, G. Cascarano, C. Giacovazzo, and A. Guagliardi, J. Appl. Cryst., 1994, 27, 1045.
12. G. M. Sheldrick, ‘SHELXL 97. Program for the Refinement of Crystal Structure’, University of
Göttingen, Göttingen, 1997.