Atropisomeric diastereoisomers from nucleophilic attack on 8-acyl-1-naphthamides

Article abstract of DOI:10.1039/b000670j

Restricted rotation about the Ar-CO bond means that 1-naphthamides bearing chiral 8-substituents may exist as pairs of diastereoisomeric atropisomers. These atropisomers are formed with good to excellent stereoselectivity for the syn-diastereoisomer by the reaction of 8-formyl-1-naphthamides with organolithiums and Grignard reagents. The reduction of 8-acyl-1-naphthamides also proceeds with syn-selectivity. The product alcohols are prone to lactonisation and also to epimerisation, and some of the apparent diastereoselectivities may be the result of thermodynamic, rather than kinetic, control.

Full text of DOI:10.1039/b000670j

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Atropisomeric diastereoisomers from nucleophilic attack on
8-acyl-1-naphthamides
Jonathan Clayden,*a Neil Westlunda and Christopher S. Framptonb
1
a Department of Chemistry, University of Manchester, Oxford Rd., Manchester, UK M13 9PL
b Roche Discovery Welwyn, 40 Broadwater Rd., Welwyn Garden City, Herts, UK AL7 3AY
Received (in Cambridge, UK) 24th January 2000, Accepted 10th March 2000
Restricted rotation about the Ar–CO bond means that 1-naphthamides bearing chiral 8-substituents may exist as
pairs of diastereoisomeric atropisomers. These atropisomers are formed with good to excellent stereoselectivity for
the syn-diastereoisomer by the reaction of 8-formyl-1-naphthamides with organolithiums and Grignard reagents.
The reduction of 8-acyl-1-naphthamides also proceeds with syn-selectivity. The product alcohols are prone to
lactonisation and also to epimerisation, and some of the apparent diastereoselectivities may be the result of
thermodynamic, rather than kinetic, control.
8-substituent.26 In the current study, none of the 8-substituted
naphthamides has nucleophilic 8-substituent, and we
expected the rates of racemisation or epimerisation to be
fast. We therefore kept reaction times to a minimum and
ensured that the products remained cold throughout the
work-up.
Introduction
a
In the previous two papers1 we described the atroposelective
attack of nucleophiles and some electrophiles on 1-naphth-
amides bearing prochiral 2-substituents. In this paper we turn
to the effect of the stereogenic amide axis of 8-substituted
1-naphthamides on the atroposelectivity of the reactions at
prochiral 8-substituents.2 Axially chiral 1,8-disubstituted naph-
thalenes have been used successfully as reagents for asymmetric
protonation,3 as chiral auxiliaries for asymmetric conjugate
addition reactions,4 and as chiral ligands for metal-catalysed
asymmetric reactions.5 The 8-substituents of 1-naphthamides
are nearer the amide axis than the 2-substituents, and we hoped
that this would mean the stereoselectivities of their reactions
would be correspondingly higher.
Results and discussion
Addition of alkyllithiums and Grignard reagents to 8-formyl-1-
naphthamides
The starting 8-substituted aldehydes were made by our
published perilithiation–Polonovski reaction sequence from
dimethylaminomethylnaphthalene.24 We treated each of the two
aldehydes 1 and 3 with alkyllithiums or Grignard reagents, as
shown in Scheme 1, and obtained mixtures of the atropisomeric
In the event, some were, but the closeness in space of the
1- and 8-substituents led to other problems of reactivity. In
addition, it is well known from the binaphthyl series6–11 that the
barrier to rotation provided by an 8-substituent is significantly
lower than that provided by a comparable 2-substituent,12 and
in some reactions we were unable to be sure whether the
observed selectivities were purely kinetic or whether they arose
through thermodynamic equilibration between the diastereo-
isomeric product atropisomers.
Rotational restriction in 1,8-biaryl naphthalenes has been
studied in detail. 1,8-Di-o-tolylnaphthalene can exist as two
diastereoisomeric atropisomers: the trans is favoured 3.21:1
over the cis at 40 ЊC, and the cis isomer converts to the trans
with a barrier of 100.8 kJ mol–1 at this temperature.13 Barriers
to interconversion of naphthalenes bearing meta-substituted
phenyl14,15 or pyridyl16–18 rings at the 1- and 8-positions are
much lower, and these compounds do not exist as atropisomeric
diastereoisomers. The conformation19,20 and racemisation21 of
enantiomeric atropisomers of 8-substituted-1-naphthamides
and their thioamide derivatives22 have been described by
Mannschreck and Kiefl, but there are no reported examples
of diastereoisomeric non-biaryl atropisomers based on a 1,8-
disubstituted naphthalene system.
8-Substituted naphthamides are most conveniently made
either by a Lossen-type rearrangement23,24 of 1,8-naphthal-
imide N-oxide or by perilithiation of 1-(dimethylamino-
methyl)naphthalene.24,25 We used both of these methods to
make a small group of amides which we proved to be chiral,
and whose rate of racemisation turned out to be influenced by
the degree of bonding interaction between the amide and the
Scheme
metallics.
1
Reactions of 8-formyl-1-naphthamides with organo-
DOI: 10.1039/b000670j
J. Chem. Soc., Perkin Trans. 1, 2000, 1379–1385
This journal is © The Royal Society of Chemistry 2000
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Table 1 Additions to 8-formyl-1-naphthamides
Reaction with 1
Reaction with 3
Thermodynamic
Ratio
syn-:anti-2
Ratio
syn-:anti-4
Ratio
syn-:anti-4
Entry
RMet
Product
Yield
Product
Yield
1
2
3
4
5
6
7
MeLi
2a
—
2b
2c
2a
2b
2c
82:18
—
89:11
>99:1
83:17
83:17
>99:1
76
—
68
69
83
64
77
4a
4a
4b
4c
4a
4b
4c
56:44
76:24
90:10
>99:1
83:17
75:25
>99:1
99
99
79
55
81
61
78
89:11
89:11
85:15
>99:1
89:11
85:15
>99:1
MeLia
n-BuLi
PhLi
MeMgBr
n-BuMgCl
PhMgBr
a In the presence of HMPA (4 equiv.).
we can be confident that the product ratios still represent closely
the kinetically controlled product ratio.
We determined the equilibrium ratios of syn- and anti-4a–c by
allowing solutions of the mixtures of diastereoisomers to stand
in CDCl3 until there was no further change in composition of
the mixture. This was not possible for 2a–c because they very
rapidly cyclised to 5 under these conditions, and we cannot be
sure that the products 2 have not already reached thermo-
dynamic equilibrium. The equilibrated ratios of the diastereo-
isomers of 4 are given in the final column of Table 1. Apart
from 4a made with MeLi, it turns out that all the reactions of 3
give product ratios close to the equilibrium value. Our ability to
obtain a ratio for 4a significantly different from the equilibrium
ratio, adds to our confidence that the work-up conditions avoid
total equilibration of 4a–c, but we still cannot be certain that
the ratios of 2a–c are under purely kinetic control.
The strong thermodynamic preference for one atropisomer
mirrors results reported for binaphthyls bearing chiral 8-
substituents,10,27 and is a further result of the proximity in space
of the 1- and 8-substituents. The stereochemical effect of this
strong peri-interaction is observable in unsymmetrically substi-
tuted 1,8-diaminonaphthalenes.28 Its effect on reactivity is even
more widespread: this same class of compounds (the “proton
sponges”) owe their powerful basicity to non-bonded 1,8-
interactions between nitrogen lone pairs,29 and similar effects
are apparent in naphthalenes bearing sulfur or selenium atoms
in the 1- and 8-positions.30,31 Non-bonded interactions force
1,8-di-tert-butylnaphthalene to adopt a twisted structure32 with
the two tert-butyl groups staggered by 40Њ and are the cause of
the remarkably high reactivity of the aromatic rings of 1,8-
disubstituted naphthalenes toward reduction,33,34 and of the
unreactivity of trigonal 8-substituents towards nucleophilic
attack.24,35 The crystal structure of syn-4c (Fig. 1) displays
properties consistent with severe repulsion between the peri-
substituents. The dihedral angle between the two peri C–C
bonds is 21Њ, and the bonds are splayed out in the plane of the
ring. The amide is twisted away from perpendicularity to avoid
Ph–Ni-Pr2 interactions.†
Conversely, when the two peri-substituents are capable of a
bonding interaction, that interaction is highly favoured. 1,8-
Cyclisations are particularly rapid24,35 – hence the instability of
2 towards lactonisation. Dunitz and co-workers36 observed
peri-bonding interactions even between poorly nucleophilic and
electrophilic groups, and we have shown that these interactions
slow the racemisation of some 8-substituted-1-naphthamides
very significantly.26 The attractive peri π–π interactions37,38
between electron-rich and -poor aryl substituents have been
proposed as the basis for the development of new non-linear
optic devices.39
Fig. 1 X-Ray crystal structure of syn-4c.
diastereoisomers of the products 2 and 4, generally in good
yield (Table 1). The ratios were determined by extracting an
aliquot immediately after the reactions had been quenched,
performing a rapid mini-workup, and analysing the aliquot
immediately by HPLC, keeping the sample on ice. The alcohols
4 could be purified, but slowly cyclised, even as solids at Ϫ18 ЊC
in the freezer, to the lactones 5. The alcohols 3, with the rather
less hindered N,N-diethylamide group, were much less stable,
and even attempted purification on silica resulted in cyclisation
to 5.
Stereochemistry was assigned to syn-4c on the basis of its
X-ray crystal structure, shown in Fig. 1. There is an intra-
molecular hydrogen bond in this structure, and the hydrogen
1
bonded proton appears as a sharp signal in the H NMR at
δ 5.2. This sharp OH signal was a common feature of the major
product diastereoisomers, and allowed us to be confident that 1
and 3 react with syn-stereoselectivity in every case.
Less certain was whether the ratios in Table 1 truly represent
the kinetic product ratios from the reactions. The half-life
for racemisation of a representative 8-alkyl-1-naphthamide,
8-(NЈ,NЈ-dimethylaminomethyl)-N,N-diisopropyl-1-
naphthamide 6, is only 5 min at 20 ЊC,12,26 and 8-substituted
naphthamides racemise significantly faster than similarly
substituted 2-naphthamides.12,26 We gained an estimate of the
barrier to epimerisation of 4 (by rotation about Ar–CO) by
following the equilibration at 10 ЊC in toluene of a 72:18 mix-
ture of syn-4a and anti-4a. Over a period of a few days, this
mixture approached thermodynamic equilibrium. Using the
method described previously,12 we obtained barriers to rotation
∆G‡syn = 92 kJ molϪ1 and ∆G‡anti = 89 kJ molϪ1. These corre-
spond to a half-life for epimerisation of 13 h at 10 ЊC, or
approximately 3 h at 20 ЊC, assuming ∆G‡ remains constant
with temperature. This barrier, while it is about 15–20 kJ molϪ1
lower than the barrier to epimerisation of the isomeric 2-
substituted alcohols,12 is sufficiently large that, at least for 4a–c
† Using Dunitz’s notation36 to describe the geometry of the peri-
disubstituted system, which we have employed before,26 θ1 = 115.9Њ,
θ2 = 122.5Њ, θ3 = 123.0Њ, θ4 = 118.2Њ, α = 74.0Њ, β = 49.9Њ, γ = 68.7Њ,
δ = 68.8Њ.
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Fig. 2 Stereoselectivity in the attack of nucleophiles on aldehydes 1 and 3.
In contrast with the reactions of 2-formyl substituted 1-
all other reactions producing 2c or 4c, the reduction of 7c gave
naphthamides, in which the sense of stereoselectivity is highly
dependent on the metal, it is almost certain that the sense of the
stereoselectivity is the same in every reaction of Table 1,
irrespective of the organometallic employed. Steric hindrance
in the starting material 2 or 4 means the formyl group must
twist out of the plane of the naphthalene ring.19,20 A suggested
transition state for the formation of the syn-diastereoisomer is
shown in Fig. 2(b): the organometallic approaches from the
least hindered direction, away from the amide, and as the new
bond forms, only the H atom of the aldehyde has to move closer
to the amide NR2. The corresponding transition state (f) for the
anti-isomer places the new O–Met bond syn to the NR2 group.
syn-Selectivity may also be favoured by chelation, which can
stabilise (b) but not (f). In one experiment, we added HMPA to
the reaction of MeLi and 3, and indeed noted increased syn-
selectivity, but it is not clear whether this arises from disruption
of chelated complexes or simply from a change in the aggre-
gation state of the nucleophile.
We have no clear explanation for the thermodynamic prefer-
ence for syn over anti: it seems likely that conformers (c) and (d)
or (g) and (h) are populated for either syn- or anti-product. But
the most stable are probably (c) and (h), since they have the most
hindered site occupied by H. Conformer (c) may furthermore
be stabilised by a hydrogen bond – this certainly corresponds
closely to the conformation in the X-ray crystal structure, but
we have no data on whether the anti-isomer is more favoured in
hydrogen-bonding solvents.
solely 4c in 90% yield. The reduction of 7a was, by contrast,
almost entirely unselective, giving a 54:46 mixture of syn-:anti-
4a in 91% yield.
While epimerisation towards thermodynamic equilibrium
may still be playing a role in determining product mixtures,
kinetic selectivity of this sort can be easily explained again by
considering conformation in the transition states leading to syn-
and anti-4 (Fig. 3). This time, we presume the size of R means
(c) and (d) are favoured over (a) and (b), but more so for R = Ph
than R = Me, for which (b) and (d) are approximately equally
stable.
Conclusion
Both kinetic stereoselectivity and thermodynamically-
controlled equilibration favour the formation of syn atropiso-
meric alcohols from nucleophilic additions to 8-acyl substituted
naphthamide. However, the products are unstable with respect
to epimerisation of the products and cyclisation to lactones.
Experimental
General experimental details have been described before.1
(Sa*,1ЈS*)- and (Sa*,1ЈR*)-N,N-Diethyl-8-(1Ј-hydroxyethyl)-1-
naphthamide, anti-2a and syn-2a
A solution of aldehyde 124 (81 mg, 0.32 mmol) in THF (2.0 ml)
at Ϫ78 ЊC under an atmosphere of nitrogen was treated with
methyllithium (0.27 ml; 1.4 M solution in ether) and stirred for
3 hours. The reaction mixture was then treated with more
methyllithium (0.27 ml, 1.4 M solution in ether), stirred for a
further 10 minutes, treated with saturated aqueous ammonium
chloride (5 ml) and allowed to warm to ambient temperature.
After extraction with dichloromethane (4 × 5 ml) the combined
organic extracts were dried (MgSO4), filtered, concentrated
under reduced pressure to afford a mixture of the alcohols anti-
2a and syn-2a (66 mg, 76%) as a brown oil [18 (anti-2a): 82 (syn-
Reduction of 8-acyl-1-naphthamides
Alcohols 4a and 4c were oxidised with Jones’ reagent at 0 ЊC
(higher temperatures led to significant formation of the
lactones 5) to give the 8-acyl-1-naphthamides 7a and 7c. These
ketones were reduced using LiBHEt3 (found to be the best
reagent for selective reduction of 2-acyl-1-naphthamides1,40
)
back to mixtures of the alcohols 4a and 4c (Scheme 2). As with
1
2a) by H NMR] containing trace amount of lactone 5a, νmax
(film)/cmϪ1 3406, 3055, 2978, 2933, 2875, 2850, 1607; δH(300
MHz, CDCl3) 7.80 (1H, d, J 8.1, ArH), 7.73 (2H, d, J 7.7,
ArH), 7.45 (1H, t, J 7.6, ArH), 7.36 (1H, t, J 7.3, ArH), 7.24
(1H, d, J 7.0, ArH), 5.51 (1H, q, J 6.0, CHOHminor), 5.28 (1H, q,
J 6.5, CHOHmajor), 3.78 (1H, m, CHAHBCH3major), 3.42 (1H,
m, CHAHBCH3major), 3.25 (2H, q, J 7.0, CH2CH3major), 3.06 (1H,
m, CHAHBCH3minor), 1.55 (3H, d, J 6.3, CH(OH)CH3major),
1.50 (3H, d, J 6.1, CH(OH)CH3minor), 1.28 (3H, t, J 7.1,
CH2CH3major), 1.05 (3H, t, J 7.1, CH2CH3major), 0.91 (3H, t,
J 7.1, CH2CH3minor); δCmajor(75 MHz, CDCl3) 173.9, 140.7,
135.1, 132.6, 130.7, 129.1, 128.2, 126.2, 125.5, 125.3, 124.1,
63.8, 43.5, 39.4, 21.8, 13.3 and 11.7; m/z (CI) 272 (15%,
M ϩ Hϩ), 254 (65%, M Ϫ OH) and 74 (100%) (Found: Mϩ,
271.1570. C17H21NO2 requires M, 271.1572).
Scheme 2 Stereoselective reduction of ketones 7.
J. Chem. Soc., Perkin Trans. 1, 2000, 1379–1385
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Fig. 3 Stereoselectivity in the attack of nucleophiles on ketones 7.
Alternatively, a solution of aldehyde 1 (81 mg, 0.32 mmol) in
in cyclohexane–diethyl ether), stirred for 3 hours, treated with
THF (2.0 ml) was treated with methylmagnesium bromide (0.13
ml, 0.38 mmol; 3 M solution in THF), stirred for 3 hours, and
treated with more methylmagnesium bromide (0.13 ml, 0.38
mmol; 3 M solution in THF). Work-up in the usual manner
afforded alcohols 2a (72 mg, 83%) as a mixture of diastereo-
isomers [17 (anti-2a): 83 (syn-2a) by 1H NMR] containing trace
amount of lactone 5a.
more phenyllithium (0.20 ml, 0.36 mmol; 1.8 M solution in
cyclohexane–diethyl ether) and stirred for a further 10 minutes.
Work-up in the usual manner afforded the alcohol syn-2c (76
mg, 69%) as a brown oil and as a single diastereoisomer (by 1H
NMR) containing a trace amount of lactone 5c, νmax (film)/
cmϪ1 3426, 3410, 3060, 3030, 2977, 2930, 2874, 2850, 1603;
δH(300 MHz, CDCl3) 7.83 (1H, d, J 8.1, ArH), 7.69 (1H, d,
J 8.1, ArH), 7.45–7.15 (8H, m, ArH), 7.10 (1H, d, J 7.3, ArH),
6.35 (1H, s, CHOH), 3.66 (1H, m, CHAHBCH3), 3.50 (1H, m,
CHAHBCH3), 3.36 (1H, m, CHAHBCH3), 3.27 (1H, m, CHAHB-
CH3), 1.19 (3H, t, J 7.1, CH2CH3), 1.10 (3H, t, J 7.2, CH2CH3);
δC(75 MHz, CDCl3) 174.0, 143.2, 141.1, 135.0, 132.5, 130.9,
129.6, 129.1, 128.7, 128.0, 126.7, 126.6, 126.2, 125.7, 124.2,
70.4, 43.7, 39.6, 13.6 and 11.9; m/z (CI) 334 (M ϩ Hϩ, 3%),
316 (3%, M Ϫ OH), 261 (4%, M Ϫ NEt2) and 74 (100%); m/z
(EI) 333 (1%, Mϩ), 316 (1%, M Ϫ OH), 261 (9%, M Ϫ NEt2)
and 49 (100%) (Found: M, 333.1734. C22H23NO2 requires M,
333.1729).
(Sa*,1ЈS*)- and (Sa*,1ЈR*)-N,N-Diethyl-8-(1Ј-hydroxypentyl)-
1-naphthamide, anti-2b and syn-2b
In the same way, a solution of aldehyde 1 (85 mg, 0.33 mmol) in
THF (2.0 ml) at Ϫ78 ЊC under an atmosphere of nitrogen was
treated with n-butyllithium (0.26 ml, 0.42 mmol; 1.6 M solution
in hexanes), stirred for 3 hours, treated with more n-butyl-
lithium (0.26 ml, 0.42 mmol; 1.6 M solution in hexanes) and
stirred for a further 10 minutes. Work up in the usual manner
gave the crude product as a brown oil. The product was dried
under high vacuum overnight to afford the alcohols anti-2b
and syn-2b (70 mg, 68%) as a brown oil and as a mixture of
Alternatively, a solution of aldehyde 1 (83 mg, 0.33 mmol) in
THF (2.0 ml) was treated with phenylmagnesium bromide (0.39
ml, 0.39 mmol; 1 M solution in THF), stirred for 3 hours, and
treated with more phenylmagnesium bromide (0.39 ml, 0.39
mmol; 1 M solution in THF). Work-up in the usual manner
afforded alcohol syn-2c (85 mg, 77%) as a single diastereo-
isomer (by 1H NMR) containing trace amounts of lactone 5c.
1
diastereoisomers [11 (anti-2b): 89 (syn-2b) by H NMR] con-
taining trace amounts of lactone 5b, νmax (film)/cmϪ1 3426, 3053,
2956, 2934, 2870, 1721, 1690, 1607; δH(300 MHz, CDCl3) 7.81
(1H, d, J 8.1, ArH), 7.72 (1H, d, J 8.1, ArH), 7.67 (1H, d, J 7.3,
ArH), 7.45 (1H, t, J 7.8, ArH), 7.35 (1H, t, J 7.4, ArH), 7.24
(1H, d, J 7.0, ArH), 5.32 (1H, br m, CHOHminor), 4.94 (1H, br
m, CHOHmajor), 4.35 (1H, br s, OHmajor), 3.76 (1H, m, NCHA-
HBCH3major), 3.45 (1H, m, NCHAHBCH3major), 3.36 (1H, m,
NCHAHBCH3major), 3.27 (1H, m, NCHAHBCH3major), 2.07
(1H, m, CHAHB(CH2)2CH3major), 1.80 (1H, m, CHAHB(CH2)2-
CH3major), 1.5–1.0 (4H, m, CH2(CH2)2CH3major), 1.30 (3H, t,
J 7.1, NCH2CH3major), 1.11 (3H, t, J 7.1, NCH2CH3major), 0.81
(3H, t, J 7.0, (CH2)3CH3major); δCmajor(75 MHz, CDCl3) 174.0,
140.0, 135.2, 132.6, 130.8, 128.9, 128.9, 126.3, 125.9, 125.5,
124.0, 68.4, 43.5, 39.4, 35.3, 29.1, 22.7, 14.0, 13.4 and 11.9;
m/z (CI) 314 (1%, M ϩ Hϩ), 296 (2%, M Ϫ OH), 241
(7%, M Ϫ NEt2) and 74 (100%); m/z (EI) 313 (0.05%, Mϩ) and
49 (100%) (Found: Mϩ, 313.2040. C20H27NO2 requires M,
313.2042).
(Sa*,1ЈS*)- and (Sa*,1ЈR*)-N,N-Diisopropyl-8-(1Ј-hydroxy-
ethyl)-1-naphthamide, anti-4a and syn-4a
A solution of aldehyde 3 (176 mg, 0.62 mmol) in THF (3 ml) at
Ϫ78 ЊC under an atmosphere of nitrogen was treated with
methyllithium (0.50 ml, 0.81 mmol; 1.6 M solution in diethyl
ether) dropwise, stirred for a further 3 hours, quenched with
saturated aqueous ammonium chloride (5 ml) and allowed to
warm to ambient temperature. The aqueous was extracted with
dichloromethane (4 × 5 ml) and the combined organic extracts
were dried (MgSO4), filtered and concentrated under reduced
1
pressure to give the crude product as an oil. H NMR of the
crude product showed the atropisomers to be present in a ratio
of 24 (anti-4a): 76 (syn-4a). Purification by flash chromato-
graphy [4:1 petrol–EtOAc] afforded a mixture of the alcohols
anti-4a and syn-4a (184 mg, 99%) as a white solid, mp 90–92 ЊC;
Rf 0.39 [2:1 petrol (bp 40–60 ЊC)–EtOAc]; νmax (film)/cmϪ1
3426, 2972, 2932, 1605; δH(300 MHz, CDCl3) 7.97–7.80 (3H, m,
ArH), 7.57 (1H, m, ArH), 7.47 (1H, m, ArH), 7.29 (1H, m,
ArH), 5.81 (1H, q, J 6.0, CHOHminor), 5.58 (1H, dq, J 3.7, 6.5,
CHOHmajor), 4.67 (1H, d, J 3.7, CHOHmajor), 4.01 (1H, septet,
J 6.7, NCHmajor), 3.78 (1H, septet, J 6.6, NCHminor), 3.67 (1H,
m, NCHmajor), 1.71 (6H, d, J 6.7, 2 × CH3major), 1.69 (3H, m,
CH3minor), 1.67 (3H, m, CH3minor), 1.65 (3H, m, CH3minor), 1.24
(3H, d, J 6.6, CH3major), 1.19 (3H, d, J 6.7, CH3minor), 1.18 (3H,
d, J 6.7, CH3major), 1.13 (3H, d, J 6.6, CH3major); δC(75 MHz,
CDCl3) 173.8major, 171.8minor, 143.2, 140.4, 135.2, 134.7, 134.0,
Alternatively, a solution of aldehyde 1 (67 mg, 0.26 mmol) in
THF (2.0 ml) was treated with n-butylmagnesium chloride (0.16
ml, 0.32 mmol; 2 M solution in THF), stirred for 3 hours, and
treated with more n-butylmagnesium bromide (0.16 ml, 0.32
mmol; 2 M solution in THF). Work-up in the usual manner
afforded alcohols 2b (52 mg, 64%) as a mixture of diastereo-
isomers [17 (anti-2b): 83 (syn-2b) by 1H NMR] containing trace
amount of lactone 5b.
(Sa*,1ЈR*)-N,N-Diethyl-8-[hydroxy(phenyl)methyl]-1-
naphthamide syn-2c
In the same way, a solution of aldehyde 1 (83 mg, 0.33 mmol) in
THF (2.0 ml) at Ϫ78 ЊC under an atmosphere of nitrogen was
treated with phenyllithium (0.20 ml, 0.36 mmol; 1.8 M solution
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130.4, 129.9, 129.1, 128.7, 128.1, 126.2, 126.0, 125.0, 124.8,
124.5, 124.3, 66.4, 63.5, 51.6, 51.0, 46.3, 45.9, 26.0, 21.0, 20.3,
20.2, 20.2, 20.1, 19.9, 19.7 and 19.4; m/z (CI) 300 (97%,
M ϩ Hϩ) and 282 (100%, M Ϫ OH); m/z (EI) 299 (3%, Mϩ)
and 49 (100%) (Found: Mϩ, 299.1891. C19H25NO2 requires M,
299.1885).
Mϩ), 324 (11%, M Ϫ OH) and 86 (100%) (Found: Mϩ,
341.2361. C22H31NO2 requires M, 341.2355).
Alternatively, a solution of aldehyde 3 (47 mg, 0.17 mmol) in
THF (1.1 ml) was treated with n-butylmagnesium chloride (0.10
ml, 0.20 mmol; 2 M solution in THF), stirred for 3 hours and
quenched with saturated aqueous ammonium chloride (5 ml).
Work up in the usual manner gave the crude product as a brown
oil. 1H NMR of the crude product showed the atropisomers to
be present in a ratio of 25 (anti-4b): 75 (syn-4b). Purification by
flash chromatography [4:1 petrol–EtOAc] afforded a mixture
of the alcohols 4b (35 mg, 61%) as a colourless oil.
Alternatively, a solution of aldehyde 3 (67 mg, 0.22 mmol) in
THF (1.5 ml) was treated with methylmagnesium bromide (0.39
ml, 0.39 mmol; 1 M solution in THF), stirred for 3.5 hours and
quenched with saturated aqueous ammonium chloride (5 ml).
1
After work-up in the usual manner, H NMR of the crude
product showed the atropisomers to be present in a ratio of 17
(anti-4a): 83 (syn-4a). Purification by flash chromatography
[4:1 petrol–EtOAc] afforded the alcohols 4a (52 mg, 81%) as a
white solid.
(Sa*,1ЈR*)-N,N-Diisopropyl-8-[1Ј-hydroxy(phenyl)methyl]-1-
naphthamide syn-4c
In the same way, a solution of aldehyde 3 (47 mg, 0.17 mmol) in
THF (1.1) was treated with phenyllithium (0.11 ml, 0.20 mmol;
1.8 M solution in cyclohexane–diethyl ether), stirred for 3 hours
and quenched with saturated aqueous ammonium chloride (5
ml). Work up in the usual manner gave the crude product as a
brown oil. 1H NMR of the crude product showed the presence
of only one diastereoisomer. Purification by flash chromato-
graphy [4:1 petrol–EtOAc] afforded the alcohol syn-4c (33 mg,
55%) as an off-white solid. Recrystallisation from ethyl acetate
by slow evaporation afforded the product as colourless blades,
νmax (film)/cmϪ1 3426, 3054, 2963, 2934, 2871, 1606; δH(300
MHz, CDCl3) 7.94 (1H, dd, J 8.2 and 1.2, ArH), 7.73 (1H, dd,
J 8.1 and 1.1, ArH), 7.42–7.16 (8H, m, ArH), 7.15 (1H, dd,
J 7.4 and 1.4, ArH), 6.50 (1H, s, CHOH), 5.29 (1H, s, OH), 4.19
(1H, septet, J 6.7, NCH), 3.67 (1H, septet, J 6.9, NCH), 1.67
(3H, d, J 6.9, CH3), 1.63 (3H, d, J 6.9, CH3), 1.30 (3H, d, J 6.5,
CH3), 1.14 (3H, d, J 6.7, CH3); δC(75 MHz, CDCl3) 173.9,
143.1, 141.4, 135.2, 133.8, 130.6, 129.6, 129.1, 128.6, 127.9,
126.6, 126.2, 124.8, 124.3, 70.2, 51.8, 46.4, 29.6, 20.4, 20.2, 20.7
and 19.8.
Alternatively, a solution of aldehyde 3 (110 mg, 0.39 mmol)
and HMPA (0.35 ml, 2.02 mmol) in THF (3 ml) at Ϫ78 ЊC
under an atmosphere of nitrogen was treated with methyl-
lithium (0.32 ml, 0.51 mmol; 1.6 M solution in diethyl ether)
dropwise, stirred for a further 4 hours, quenched with saturated
aqueous ammonium chloride (5 ml) and allowed to warm to
ambient temperature. The aqueous was extracted with diethyl
ether (4 × 5 ml) and the combined organic extracts were dried
(MgSO4), filtered and concentrated under reduced pressure to
give the crude product as an oil. 1H NMR of the crude product
showed the atropisomers to be present in a ratio of 24 (anti-4a):
76 (syn-4a). Purification by flash chromatography [4:1 petrol–
EtOAc] afforded the alcohols 4a (184 mg, 99%) as a white solid.
Alternatively, a solution of ketone 7a (23 mg, 0.08 mmol) in
THF (1.5 ml) at Ϫ78 ЊC under an atmosphere of nitrogen was
treated with Super Hydride (0.20 ml, 0.20 mmol; 1 M solution
in THF) dropwise, stirred for a further 5 hours, warmed to
ambient temperature and added to a solution of 30% hydrogen
peroxide (1 ml) and 10% aqueous sodium hydroxide (1 ml). The
aqueous was extracted with dichloromethane (4 × 5 ml) and
the combined organic extracts were dried (MgSO4), filtered
and concentrated under reduced pressure to give the crude
Alternatively, by the method used for the reduction of 7a, a
solution of ketone 7c (51 mg, 0.14 mmol) in THF (2 ml) and
Super Hydride (0.28 ml, 0.28 mmol; 1 M solution in THF)
1
product as an oil. H NMR of the crude product showed the
1
gave a crude product as an oil. H NMR of the crude product
atropisomers to be present in a ratio of 46 (anti-4a): 54 (syn-4a).
Purification by flash chromatography [4:1 petrol–EtOAc]
afforded the alcohols 4a (21 mg, 91%) as a white solid.
showed a single atropisomer, anti-4c. Purification by flash
chromatography [2:1 petrol–EtOAc] gave the alcohol anti-
4c(46 mg, 90%) as a white solid.
(Sa*,1ЈS*)- and (Sa*,1ЈR*)-N,N-Diisopropyl-8-(1Ј-hydroxy-
pentyl)-1-naphthamide, anti-4b and syn-4b
3-Methyl-1H,3H-benzo[de]isochromen-1-one 5a
Alcohols 2a (56 mg, 0.21 mmol) were eluted through silica gel
[2:1 petrol (bp 40–60 ЊC)–EtOAc] to give the lactone 5a (39 mg,
94%) as a sticky pale yellow solid, λmax/nm (εmax) (CH2Cl2) 238
(19940), 314 (5647); νmax (film)/cmϪ1 3238, 3216, 1719; δH(300
MHz, CDCl3) 8.46 (1H, dd, J 7.1 and 1.1, ArH), 8.17 (1H, dd,
J 8.4 and 1.1, ArH), 7.91 (1H, d, J 8.2, ArH), 7.70 (1H, dd, J 8.1
and 7.3, ArH), 7.62 (1H, dd, J 8.2 and 7.3, ArH), 7.43 (1H,
J 7.1, ArH), 6.05 (1H, q, J 6.7, CHCH3), 1.86 (3H, d, J 6.7,
CH3); δC(75 MHz, CDCl3) 164.1, 133.5, 132.4, 132.1, 129.1,
127.5, 126.8, 126.5, 126.4, 122.1, 120.2 and 24.5; m/z (CI) 199
(100%, M ϩ Hϩ) and 183 (M Ϫ CH3); m/z (EI) 198 (31%, Mϩ),
183 (99%, M Ϫ CH3) and 127 (100%) (Found: Mϩ, 198.0680.
C13H10O2 requires M, 198.0681).
By the method described above, a solution of aldehyde 3 (66
mg, 0.23 mmol) in THF (1.5 ml) was treated with n-butyl-
lithium (0.18 ml; 1.6 M solution in hexanes), stirred for 3 hours
and quenched with saturated aqueous ammonium chloride
(5 ml). Work-up in the usual manner gave the crude product
1
as a brown oil. H NMR of the crude product showed the
atropisomers to be present in a ratio of 10 (anti-4b): 90 (syn-4b).
Purification by flash chromatography [4:1 petrol–EtOAc]
afforded a mixture of the alcohols anti-4b and syn-4b (62 mg,
79%) as a colourless oil, Rf 0.47 [2:1 petrol–EtOAc]; νmax (film)/
cmϪ1 3428, 3053, 2961, 2934, 2871, 1606; δH(300 MHz, CDCl3)
7.79 (1H, dd, J 8.2 and 1.1, ArH), 7.72 (1H, d, J 8.1, ArH), 7.66
(1H, d, J 7.3, ArH), 7.45 (1H, t, J 7.7, ArH), 7.35 (1H, t, J 7.1,
ArH), 7.19 (1H, dd, J 7.3 and 1.2, ArH), 5.53 (1H, dd, J 8.4
and 3.3, CHOHminor), 5.10 (1H, m, CHOHmajor), 4.65 (1H, d,
J 3.2, OHmajor), 3.98 (1H, septet, J 6.6, NCHmajor), 3.57 (1H,
septet, J 6.9, NCHmajor), 2.14 (1H, m, CHAHB(CH2)2CH3major),
1.83 (1H, m, CHAHB(CH2)2CH3major), 1.62 (3H, d, J 6.9, NCH-
CH3major), 1.53 (3H, d, J 6.7, NCHCH3major), 1.5–1.0 (4H, m,
CH2(CH2)2CH3major), 1.15 (3H, d, J 6.6, NCHCH3major), 1.10
(3H, d, J 6.7, NCHCH3major), 0.84 (3H, t, J 7.3, CH2(CH2)2-
CH3major); δCmajor(75 MHz, CDCl3) 173.8, 140.1, 135.3, 134.0,
130.5, 129.0, 128.7, 126.3, 125.6, 124.7, 124.1, 68.4, 51.6, 46.3,
35.3, 29.4, 23.1, 20.5, 20.2, 20.1, 20.0 and 14.0; m/z (CI) 342
(46%, M ϩ Hϩ) and 324 (100%, M Ϫ OH); m/z (EI) 341 (5%,
3-Butyl-1H,3H-benzo[de]isochromen-1-one 5b
Alcohols 2b (42 mg, 0.13 mmol) were eluted through silica gel
[2:1 petrol–EtOAc] to give the lactone 5b (30 mg, 97%) as a pale
yellow solid, Rf 0.51 [2:1 petrol–EtOAc]; νmax (film)/cmϪ1 3057,
2956, 2931, 2870, 2861, 1758, 1729; δH(300 MHz, CDCl3) 8.44
(1H, dd, J 7.2 and 1.1, ArH), 8.14 (1H, dd, J 8.4 and 1.1, ArH),
7.88 (1H, d, J 8.2, ArH), 7.68 (1H, dd, J 8.2 and 7.3, ArH), 7.60
(1H, dd, J 8.2 and 7.1, ArH), 7.40 (1H, d, J 7.1, ArH), 5.92 (1H,
t, J 5.9, CH(CH2)3CH3), 2.07 (2H, m, CHCH2(CH2)2CH3),
1.60–1.24 (4H, m, CHCH2(CH2)2CH3), 0.90 (3H, t, J 7.3, CH3);
δC(75 MHz, CDCl3) 164.3, 133.5, 132.1, 131.3, 128.9, 127.9,
J. Chem. Soc., Perkin Trans. 1, 2000, 1379–1385
1383

View Article Online
126.7, 126.4, 126.3, 122.3, 81.1, 39.0, 26.4, 22.3 and 13.8; m/z
(CI) 241 (100%, M ϩ Hϩ) and 183 (3%, M Ϫ C4H9); m/z (EI)
240 (14%, Mϩ) and 183 (100%, M Ϫ C4H9) (Found: Mϩ,
240.1146. C16H16O2 requires M, 240.1150).
stream of the diffractometer. C24H27NO2, M = 361.47, mono-
clinic, a = 9.358(2), b = 11.813(3), c = 9.917(3) Å, β = 114.44(2)Њ,
U = 998.0(5) Å3, T = 123(1) K, space group P21 (no. 4), Z = 2,
Dc = 1.203 g cmϪ3, µ(Mo-Kα) = 0.076 mmϪ1. Data collected on
a Bruker AXS SMART CCD diffractometer, 10012 reflections
measured, data truncated to 0.80 Å (θmax 26.37Њ, 99.8% com-
plete), 4011 reflections unique (Rint = 0.0140).42 Final agreement
factors for 252 parameters and 1 restraint gave R1 = 0.0279,
wR2 = 0.0734 and GOF = 1.004 based on all 4011 data, final
3-Phenyl-1H,3H-benzo[de]isochromen-1-one 5c
Alcohol syn-2c (63 mg, 0.19 mmol) was eluted through silica gel
[2:1 petrol–EtOAc] to give the lactone 5c41 (47 mg, 95%) as a
pale yellow solid, νmax (film)/cmϪ1 3058, 3033, 2972, 2928, 2872,
2851, 1725; δH(300 MHz, CDCl3) 8.41 (1H, dd, J 7.3 and 1.1,
ArH), 8.10 (1H, dd, J 8.4 and 1.0, ArH), 7.82 (1H, d, J 8.4,
ArH), 7.63 (1H, dd, J 8.2 and 7.4, ArH), 7.44 (1H, m, ArH),
7.30 (5H, m, ArH), 7.12 (1H, d, J 7.1, ArH), 6.77 (1H, s,
CHPh); δC(75 MHz, CDCl3) 167.2, 139.9, 133.7, 130.5, 129.5,
128.9, 128.8, 128.4, 127.7, 127.2, 126.5, 124.5 and 120.4; m/z
(CI) 216 (100%, M ϩ Hϩ); m/z (EI) 260 (29%, Mϩ) and 86
(100%) (Found: Mϩ, 260.0835. C18H12O2 requires M, 260.0837).
difference map ϩ0.31 and Ϫ0.44 eÅϪ3 43
.
Acknowledgements
We are grateful to the EPSRC and Roche Discovery (Welwyn)
for a CASE award (to N. W.), to Zeneca for an unrestricted
grant, to the Royal Society for an Equipment Grant, and to
Dr Francis Wilson for helpful discussions.
N,N-Diisopropyl-8-acetyl-1-naphthamide 7a
References
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A solution of alcohols 4a (161 mg) in acetone (5.5 ml) at 0 ЊC
was treated with Jones reagent (0.87 ml of a solution of CrO3
(2.5 g): conc. H2SO4 (2 ml): water (8 ml); 1.71 mmol) and stirred
for a further 45 minutes. The reaction mixture was added to a
solution of saturated aqueous sodium hydrogen carbonate (50
ml) and extracted with ethyl acetate (4 × 30 ml). The combined
organic extracts were washed with water (50 ml), dried
(MgSO4), filtered and concentrated under reduced pressure to
give the crude product. Purification by flash chromatography
on silica gel [3:1 petrol–EtOAc] afforded the ketone 7a (115 mg,
72%) as a white solid, λmax/nm (εmax) (CH2Cl2) 232 (22600), 294
(6111); Rf 0.39 [2:1 petrol–EtOAc]; νmax (film)/cmϪ1 2996, 2978,
2928, 1691, 1621; δH(300 MHz, CDCl3) 7.81 (1H, d, J 8.1,
ArH), 7.76 (1H, d, J 8.0, ArH), 7.48 (1H, d, J 7.0, ArH), 7.41–
7.30 (3H, m, ArH), 4.18 (1H, septet, J 6.6, NCH), 3.46 (1H,
septet, J 6.9, NCH), 2.63 (3H, s, COCH3), 1.54 (3H, d, J 6.7,
NCHCH3), 1.41 (3H, d, J 6.7, NCHCH3), 1.36 (3H, d, J 6.6,
NCHCH3), 1.22 (3H, d, J 6.6, NCHCH3); δC(75 MHz, CDCl3)
203.6, 171.5, 140.0, 135.3, 135.2, 131.1, 129.8, 126.8, 125.4,
125.1, 124.9, 124.5, 51.5, 45.8, 29.7, 20.8, 20.7 and 20.3; m/z
(CI) 298 (100%, M ϩ Hϩ), 254 (4%, M Ϫ COCH3) and 197
(11%, M Ϫ NiPr2); m/z (EI) 254 (10%, M Ϫ COCH3) and 197
(49%, M Ϫ NiPr2) (Found: M ϩ Hϩ, 298.1806. C19H23NO2
requires M ϩ H, 298.1807).
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N,N-Diisopropyl-8-benzoyl-1-naphthamide 7c
In the same way, a solution of alcohols 4c (175 mg, 0.49 mmol)
in acetone (5 ml) at 0 ЊC was treated with Jones’ reagent (0.78
ml). Work-up and purification by flash chromatography [3:1
petrol–EtOAc] afforded the ketone 7c (140 mg, 81%) as a white
solid, mp 143–145 ЊC, Rf 0.35 [3:1 petrol–EtOAc]; νmax (film)/
cmϪ1 3056, 2973, 2930, 2876, 1663, 1624; δH(300 MHz, CDCl3)
8.1–7.9 (5H, m, ArH), 7.7–7.4 (6H, m, ArH), 4.36 (1H, septet,
J 6.6, NCH), 3.50 (1H, septet, J 6.9, NCH), 1.58 (3H, d, J 6.6,
CH3), 1.40 (3H, d, J 6.9, CH3), 1.34 (3H, d, J 6.6, CH3), 1.28
(3H, d, J 6.9, CH3); δC(75 MHz, CDCl3) 196.4, 171.0, 137.6,
137.3, 135.5, 135.4, 132.5, 131.1, 130.1, 129.8, 128.5, 127.9,
127.8, 125.3, 125.0, 124.1, 51.5, 45.7, 20.9, 20.9, 20.5 and 20.2;
m/z (CI) 360 (100%, M ϩ Hϩ) and 259 (86%, M Ϫ NiPr2); m/z
(EI) 359 (6%, Mϩ) and 259 (100%, M Ϫ NiPr2) (Found: Mϩ,
359.1882. C24H25NO2 requires M, 359.1885).
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‡ CCDC reference number 207/414. See http://www.rsc.org/suppdata/
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J. Chem. Soc., Perkin Trans. 1, 2000, 1379–1385
1385