Studies in the cycloproparene series: Chemistry of 1-acyl-1H-cyclopropa[b]naphthalenes and synthesis of cyclopropa[b]naphthalenylidene enol ethers

Article abstract of DOI:10.1016/S0040-4020(01)00234-4

The 1H-cyclopropa[b]naphthalenyl anion reacts with N,N-dimethylamides to provide C-1 acyl derivatives in good yield in what are rare examples of mono-substitution in the cycloproparene series. The availability of these acylcycloproparenes provides for subsequent benzylic proton abstraction and enolate ion interception to give O-silyl and O-phosphinate derivatives. This reaction sequence leads to the first cyclopropa[b]naphthalenylidene enol ethers and provides the only example of exocyclic alkene formation taking place in one step from the benzylic centre. Protonation of the acyl derivatives by mineral acid triggers three-membered ring opening to 2,3-disubstituted naphthalenes rather than 2-monosubstituted analogues that typically arise from protonation at the aromatic ring. Upon thermolysis ring expansion to a naphthofuran occurs.

Full text of DOI:10.1016/S0040-4020(01)00234-4

TETRAHEDRON
Pergamon
Tetrahedron 57 92001) 3529±3536
Studies in the cycloproparene series: chemistry of
1-acyl-1H-cyclopropa[b]naphthalenes and synthesis of
cyclopropa[b]naphthalenylidene enol ethers
Brian Halton,a,p Carissa S. Jonesa and Davor Margeticb
aSchool of Chemical and Physical Sciences, Victoria University of Wellington, P.O. Box 600, Wellington, NewZealand
bCentre for Molecular Architecture, Central Queensland University, Rockhampton, Queensland 4702, Australia
Received 12 September 2000; accepted 16 November 2000
AbstractÐThe 1H-cyclopropa[b]naphthalenyl anion reacts with N,N-dimethylamides to provide C-1 acyl derivatives in good yield in what
are rare examples of mono-substitution in the cycloproparene series. The availability of these acylcycloproparenes provides for subsequent
benzylic proton abstraction and enolate ion interception to give O-silyl and O-phosphinate derivatives. This reaction sequence leads to the
®rst cyclopropa[b]naphthalenylidene enol ethers and provides the only example of exocyclic alkene formation taking place in one step from
the benzylic centre. Protonation of the acyl derivatives by mineral acid triggers three-membered ring opening to 2,3-disubstituted naphtha-
lenes rather than 2-monosubstituted analogues that typically arise from protonation at the aromatic ring. Upon thermolysis ring expansion to
a naphthofuran occurs. q 2001 Elsevier Science Ltd. All rights reserved.
Although the chemistry of the cycloproparenes, e.g. 1, has
received signi®cant attention over the past years,1±6 the
number of examples of compounds carrying a single C-1
substituent are remarkably few. Thus while Eaborn and
co-workers7,8 were able to isolate the monosilyl cyclo-
propabenzene derivative 3a, all attempts to obtain the
equivalent naphthalene analogue 3b led to the disilane 5b
instead 9Scheme 1).6,9,10 Base-induced proton abstraction of
3a and desilylation of 5a and 5b gives the silicon-stabilized
anions 4a and 4b that have been used in a range of Peterson
ole®nations to provide C-1 exocyclic alkenes 6 9alkylidene-
cycloproparenes) in what has become the major pathway to
this class of compounds.6,11±13 An alternative route to such
compounds14 involves trapping 4b with a modi®ed carbonyl
R
R
R
R
R
R
SiMe3
H
Me3SiCl
BuLi
H
1
2
3
R'CONMe2
a: R = H
b: RR = benzo fused
BuLi
R
R
R
R
R
R
COR'
H
SiMe3
SiMe3
KOBu-t
Me3SiCl
SiMe3
9
5
7
4
R1R2CO
R3COX
R
R
R
R
R
R
R3
R4
SiMe3
COR3
R1
R2
[R4]-
-Me3SiO-
8
6
Scheme 1.
Keywords: arenes; alkenes; bicyclic aromatics; carbonyl compounds; enol ethers; enolates; fulvenes; molecular modelling; naphthalenes; phosphonic acid
ester; rearrangements; silicon compounds; strained compounds.
Corresponding author. Tel.: 164-4-463-5954; fax: 164-4-463-5241; e-mail: brian.halton@vuw.ac.nz
p
0040±4020/01/$ - see front matter q 2001 Elsevier Science Ltd. All rights reserved.
PII: S0040-4020901)00234-4

3530
B. Halton et al. / Tetrahedron 57 22001) 3529±3536
O
OH
+H+
-H+
R
R
1b
2b
H
H
10: R = Ph
11: R = Me
H+
HO
R
H
O
CH2
H
NMe2
NMe2
O
12
HCl
Cl-
Cl-
O
O
NMe2
R
H
H
NMe2
Cl
O
H
Cl
Cl
15
13: R = Ph
14: R = Me
Scheme 2.
compound to give a 1-acyl-1-trimethylsilyl derivative 7b
which, in turn, reacts with an appropriate nucleophile at
the carbonyl carbon atom to induce deoxysilylation and
formation of alkene 8b.
ment with HCl these compounds undergo easy ring opening
but do not provide the monosubstituted arenes expected on
the basis of typical protonation of the cycloproparene p
framework 9Scheme 2).21±23 Rather, it is the electrophilic
carbonyl group that is protonated, thereby facilitating
cleavage of the three-membered ring which, in turn, requires
capture of the nucleophile at the arene site; the 2-chloro-3-
[9substituted)methyl]naphthalenes 13±15 are formed in
yields of 60±74%. Although 20-chlorophenylpropan-2-
one24±26 and 2-920-chlorophenyl)-1-phenylethanone27,28 are
known, the naphthalene analogues 13±15 have not been
recorded previously. Their structures are assigned with
con®dence from the spectroscopic data 9Section 1) and
especially the appearance of broadened singlets for the
9now) non-equivalent para protons H-1 97.70±7.85 ppm)
and H-4 97.88±7.93 ppm), with their corresponding carbon
resonances in the ranges 130.2±130.6 and 127.4±
127.7 ppm, respectively. The benzylic protons for 13
and 14 appear at 4.59 and 4.00 ppm whereas the tertiary
ArCH9CONMe2)2 of 15 is at 5.56 ppm. The methyl groups
of the bis9dimethylamido) derivative 15 appear as two six-
proton singlets at 2.94 and 3.02 ppm, respectively, as is
expected on the basis of restricted rotation about such
The capture of 2 or 4 with electrophilic species other than
those described above has proved more dif®cult. The studies
have attracted less attention but they have shown that the
chemistry of the C-1 cyclopropanaphthalenyl anion is
frustrated by its fast protonation and by the formation of
monosubstituted derivatives that are dif®cult to isolate.15±17
Nonetheless, monosilyl 3b has been isolated from the
desilylation of 5b and protonation of 4b, although particular
care was needed.15 A modi®cation of the reaction procedure
from 1b also provided15 1-acetyl and 1-benzoyl 9and 1,1-
dicarboxamido) derivatives, cf. 9b, via the interception of
2b 9Scheme 2). It is the chemistry of these last compounds
that forms the basis of the present paper. The location of
electron withdrawing functionality adjacent to the cyclo-
proparenyl C-1 centre in 9 opens up the possibility of
chemistry in which the electron demand is reversed from
that normally observed in the electrophilic opening of the
cycloproparene three-membered ring; this last path is
illustrated for the formation of 2-9chloromethyl)naphthalene
from 1b in Scheme 2.1±4 Furthermore, the presence of a
benzylic a hydrogen atom in 9 augurs well for enolate ion
formation from C-1 with direct formation of an exocyclic
ole®n, while the location of the carbonyl group suggests that
thermolysis and/or photolysis will provide naphtho[b]furans
from cleavage of the three-membered ring.18±20 We report
herein on the ring opening reactions of 1-acylcyclo-
propa[b]naphthalenes and on the formation and characteri-
zation of cycloproparenylidene enol ethers.
29±32
CO±Nbonds.
In contrast to the behaviour described above, treatment of
the cycloproparenes 10 and 11 with base 9BuLi) is expected
to effect the removal of the benzylic proton H-1 and
generate the enolate anions 16 and 17 9Scheme 3). As
enolates can be captured by electrophiles at both carbon
and oxygen, we sought to effect the latter since this would
provide new and novel alkylidenecycloproparenes
generated for the ®rst time in one step from the cyclo-
proparene simply by proton removal at C-1. As discussed
above, the conventional method for preparation of methyl-
idenecycloproparenes is by Peterson ole®nation from
the silyl derivatives employing a carbonyl-containing
1-Benzoyl- 910), 1-acetylcyclopropa[b]naphthalene 911),
and the dicarboxamide derivative 12 were prepared from
1b in moderate yields, as described previously.15 On treat-

B. Halton et al. / Tetrahedron 57 22001) 3529±3536
3531
O
O
H
O
BuLi
H+
R1
R1
R1
10: R1 = Ph
11: R1 = Me
16: R1 = Ph
17: R1 = Me
(t-Bu)2PCl
R2Cl
O
3
6
2
O-P(Bu-t)2
O-P(Bu-t)2
OR2
R1
O2
1
8
Ph
Ph
7
18: R1 = Ph; R2 = Me3Si
24
23
19: R1 = Ph; R2 = t-BuMe2Si
20: R1 = Ph; R2 = t-BuPh2Si
21: R1 = Me; R2 = t-BuMe2Si
22: R1 = Me; R2 = t-BuPh2Si
Scheme 3.
compound and it has yielded almost one hundred exocyclic
alkene derivatives.6,10,33 In the event, use of the base with 10
followed by addition of chlorotrimethylsilane led to an
unstable solid that provided spectroscopic data compatible
with enol ether 18. In particular, the C-1 benzylic proton of
10 95.34 ppm) was absent, the formerly equivalent H-2/7
97.78 ppm) were non-equivalent and shifted to 7.31 and
7.41 ppm and the protons of the new trimethylsiloxy
group appeared at 0.46 ppm. The 13C NMR spectrum
showed the absence of the carbonyl carbon of the substrate
10 9189.6 ppm) but provided characteristically shielded and
distinct signals for C-2 9Z with respect to the silyloxy group)
and C-7 9E with respect to the silyloxy group) of 18 at 104.2
and 104.9 ppm, respectively, that provide adequate proof for
retention of the cyclopropanaphthalene framework.1±6,11,12
In addition, a shielded C-1 ole®nic resonance was recorded
at 96.0 ppm and the trimethylsiloxy carbons resonated at
0.90 ppm. Unfortunately all attempts to isolate the pure
compound resulted in its decomposition, likely from traces
of water, as it is well known that trimethylsilyl enol ethers
are very sensitive to it and to acid.34
By employing sterically more demanding t-butyldimethyl-
and t-butyldiphenyl-chlorosilanes with 10 the siloxyalkenes
19 and 20 were isolated in yields of 57 and 60%, respec-
tively; the acetyl derivative 11 is likewise transformed into
enol ethers 21 and 22 but they are markedly less stable
9Section 1). The structures of these methylidenecyclopro-
panaphthalenes follow from their spectroscopic data. The
bright yellow t-butyldimethyl derivative 19 displays methyl
proton resonances at d 0.48 9OSiMe2) and 1.19 9OSiBu-t)
while the C-8 silyl ether and phenyl substituents cause non-
equivalence in H-2/7 which appear at d 7.29/7.40; the corre-
sponding carbon resonances are at 104.1/104.9 while C-1
and C-8 appear at 95.9 and 135.8 ppm, respectively. The
data recorded for the yellow t-butyldiphenyl derivative 20
have many similarities and show an OSiBu-t 9d 1.30) and
shielded and deshielded ole®nic carbons 9C-1 and C-8: d
97.5 and 136.9), but it is the non-equivalence of H-2 and
H-7 that shows the most dramatic change; H-2 9Z to the O
atom) resonates 1.5 ppm to higher ®eld than H-7 9d 5.78 vs
7.27). The C-2/7 resonances differ in chemical shift by
1 ppm 9d 104.9/103.9), a value somewhat larger than
normal.6 Because of the large chemical shift difference
between H-2 and H-7, HMBC correlations for the assign-
ment of H-3 and H-6 9and their respective carbon
resonances) are straightforward 9Section 1). It is abundantly
clear that the dramatic difference in the environment of H-2
and H-7 in 20 is a result of the sterically very demanding
diphenyl9t-butyl)silyl group. Semiempirical calculations
at the restricted Hartree±Fock level using the AM1
Figure 1. Two views of the favoured conformation of siloxyalkene 20
showing the shielding of H-2 by an Si-Ph group; the distance H-2 to ring
centre is 411 ppm.

3532
B. Halton et al. / Tetrahedron 57 22001) 3529±3536
R1
R1
O
R2
∆
R2
R2
or hν
R1
O
O
25
10: R1 = H; R2 = Ph
11: R1 = H; R2 = Me
12: R1 = CONMe2; R2 = NMe2
26: R1 = H; R2 = Ph
27: R1 = H; R2 = Me
28: R1 = CONMe2; R2 = NMe2
Scheme 4.
method35,36 place H-2 in the shielding cone of one of the
silicon phenyl substituents in the most favoured conformer
9546 kJ mol21), as shown in Fig. 1. The distance from the
centre of this pendant phenyl ring to H-2 is 411 ppm and it is
twisted 708 with respect to the plane carrying the cycloprop-
arenyl moiety. The range of isomers derived from rotations
about the C-8±O, O±Si, and Si±Cipso bonds of this ¯exible
molecule all fall within ca. 12 kJ mol21. The electronic
absorption spectra of these brightly coloured compounds
show little solvatochromy between hexane and acetonitrile
but there seems little doubt that the molecules typify the
polar alkylidenecycloproparenes and have charge separa-
tion.6 The assignment of structure to the analogous, though
sterically somewhat less crowded, t-butyldimethylsilyl enol
ether 21 from the acetyl-substituted 11 follows by analogy
but the compound undergoes easy oxidation during
attempted puri®cation. In contrast, the more bulky diphenyl
derivative 22 9dH 5.99, H-2; 7.04, H-7) is formed in only
low yield and could not be obtained pure prior to its decom-
position. It seems likely that the presence of the enolizable
MeCO-centre also provides for alternative, competing
reaction pathways.
9dH 3.18 and 3.19; dC 35.2 and 39.3). In the same way, the
C-1 acetyl derivative 11 provides the known38,39 analogous
product 27 but the yield is only 20%. With this and the
phenyl substituted substrate 10, added scope likely exists
for alternative reactions at least formally through diradical
25. Thus dimerizations40,41 and involvement of the C-8
phenyl group of 10 through radical insertions42±44 become
relevant. It is not surprisingly, therefore, that the 2-phenyl-
naphthofuran 26 is isolated in low 97%) yield but it proved
to be the only identi®able product from a multi-component
mixture formed upon thermolysis of 10 at 808C. In contrast,
reaction in the solid state at 1018C gives some 17% of 26
while the photo-rearrangement 9254 nm) provides the same
product in a meagre 5% yield.
In conclusion, we have demonstrated that the novel C-1
acylcycloproparenes 10±12 undergo ring opening in an
acid medium. The ortho-disubstituted products are formed
in reactions triggered by enol formation. This contrasts with
electrophilic addition to the aromatic p framework and
opening to a benzylic cation as observed in simpler cyclo-
proparenes. The formation of enolate ion upon base removal
of the C-1 hydrogen atom has been demonstrated from trap-
ping with sterically congested chlorosilanes. This has
provided the ®rst example of cycloproparenylidene enol
ethers whose ultraviolet absorptions are compatible with
extended conjugation and `push±pull' character within the
molecules. The thermal behaviour of these acyl derivatives
compares well with that of C-1 esters reported some 30
years ago and has provided new and novel naphthofurans.
We continue to explore the chemistry of the cycloproparene
framework and in particular the development of more
extended conjugation through less common functionality
at C-1.
Despite the drawbacks associated with acetylcycloprop-
arene 11, di-t-butylchlorophosphine intercepts phenyl
substituted enolate 16. Work-up in a manner analogous to
that employed for the siloxy ethers 19 and 20 provides
product, but it is not the phosphinous acid ester 23 that is
isolated. Rather the phosphonic acid ester 24 is the bright
yellow solid obtained and its formation is presumed to result
from aerial oxidation37 of initially formed 23. The two
t-butyl groups exhibit a phosphorus-coupled proton doublet
93JP±Hˆ14.7 Hz) in the 1H NMR spectrum and the C±H92/7)
groups appear at d 7.53/106.6 and 7.65/108.6; the phos-
phorus resonance is at 68.6 ppm.
Upon thermolysis and/or photolysis 1,1-diester-substituted
cycloproparenes are known to provide benzofurans from
ring expansion involving the carbonyl group.18±20 Compar-
able reactions of the acylcycloproparenes 10±12 described
herein, therefore, should result in novel and new
naphtho[b]furans 9Scheme 4). This is borne out from re¯ux-
ing a solution of the diamide 12 in benzene. Rearrangement
occurs to give the aminofuran 28 quantitatively 9Section 1).
At ambient temperature rotation about the CO±Nbond 29±32
in this compound is comparable with the time-scale of NMR
measurement in d-chloroform solution as the CONMe2
protons appear as a broad singlet 9d 3.17) but the resonance
of the methyl carbons is not discernible above the baseline.
HSQC and HMBC experiments allow for the location of this
chemical shift at d ca. 35.2. At 2208C rotation is slowed
and the signals are clearly evident in the expected 1:1 ratios
1. Experimental
1.1. General
Microanalyses were performed by the Analytical Facility of
Otago University, Dunedin. Accurate mass measurements
were recorded by Mr O. Zubkov on a PE Biosystems
Mariner spectrometer operating in electrospray mode except
1
where stated otherwise. H and 13C NMR spectra were
recorded on a Varian Unity INOVA 300 MHz instrument
for d-chloroform solutions using the residual solvent peak as
internal standard; the 31P NMR spectrum 9same instrument)
used the P atom of 10% phosphoric acid in D2O as
0.00 ppm. NMR multiplicities are de®ned by the usual nota-
tion and coupling constants are in hertz. The assignments of
1
13C and H NMR resonances were made with the aid of

B. Halton et al. / Tetrahedron 57 22001) 3529±3536
3533
1
1
DEPT and H±1H COSY and 13C±1H HSQC experiments,
93.67), 281 93.67), 290 nm 9log e 3.49). H N MRd 2.26
9s, Me), 4.00 9s, CH2), 7.47±7.50 9m, H6/7), 7.70 9bs, H1),
7.73±7.80 9m, H5/8), 7.90 9bs, H4); 13C N MRd 29.7 9Me),
48.6 9CH2), 126.4/126.792) 9C6 and C7), 126.797)/127.4 9C5
and C8), 127.7 9C4), 130.6 9C1), 130.7 9C2 or C3), 131.9
9C8a or C4a), 132.2 9C3 or C2), 133.2 9C4a or C8a), 205.3
9CO).
and heteronuclear multiple bond connectivity 9HMBC)
experiments. IR spectra of solid samples were recorded
for KBr disks using a Biorad FTS 7 spectrophotometer.
UV measurements were acquired from a Hewlett±Packard
8452A diode array spectrophotometer. Melting points were
determined on a Reichert hot-stage melting point apparatus
and are uncorrected.
9c) From 1215 9100 mg, 0.35 mmol) after 168 h was
Thin layer chromatographic 9TLC) analyses were
performed using Merck Kieselgel 9Alufoilen) 60 F254 to a
thickness of 0.2 mm. Components were detected under an
ultraviolet lamp at 254 or 350 nm, or in an iodine chamber.
Preparative TLC plates were coated with Merck Kieselgel
GF254 to a thickness of 0.75 mm and radial chromatography
plates were coated with Merck Kieselgel 60 GF254 to a
thickness of 2.0 or 4.0 mm. Column chromatography
obtained
2-chloro-3-[bis-N,N-dimethylcarboxamido)-
methyl]naphthalene -15) 984 mg, 74%) as a pale yellow
solid from radial chromatography 9ethyl acetate elution); an
analytical sample was obtained from dichloromethane/light
petroleum 91:1) as colourless blocks, mp 145±1468C
9Found: C, 63.7; H, 6.0; N, 8.8; Cl, 10.9; [M1H]1
319.1223. C17H19O2N2Cl requires: C, 64.0; H, 6.0; N, 8.8;
Cl, 10.0%; [M1H]1 319.1208). nmax 3059, 2924, 2854,
1656, 1495, 1455, 1439, 1385, 1352, 1271, 1205, 1129,
1054, 1017, 959, 880, 851, 755 cm21. lmax 9MeCN) 231
È
employed Riedel de Haen silica gel S 9230±400 ASTM)
unless otherwise stated.
1
94.67), 276 nm 9log e 3.55). H N MRd 2.94 9s, 2£NMe),
1.1.1. Reaction of the 1-acyl-1H-cyclopropa[b]naphtha-
lenes with mineral acid. To the stirred 1-acyl-1H-cyclo-
propa[b]naphthalene 957±100 mg, 0.31±0.41 mmol) in
THF 95 ml) under nitrogen was added HCl 92 M, 1 ml,
2 mmol) and the stirring continued at ambient temperature
until the reaction was complete 9TLC). The yellow product
mixture was poured into CH2Cl2/H2O 91:1; 100 ml), the
phases were separated, and the aqueous phase extracted
9CH2Cl2, 3£15 ml). The combined organic layers were
washed 9H2O, 50 ml), dried 9MgSO4), and concentrated
under reduced pressure to an oily yellow solid that was
puri®ed by radial chromatography.
3.02 9s, 2£NMe), 5.56 9s, ArCH), 7.42±7.49 9m, H6/7),
7.70±7.73 9m, H5), 7.79±7.83 9m, H8), 7.84 9bs, H1),
7.88 9bs, H4); 13C N MRd 36.0 92£NMe), 37.2 92£NMe),
51.3 9ArCH), 126.3/126.9 9C6 and C7), 126.4 9C5), 127.4
9C4), 128.1 9C8), 129.9/131.0 9C2 and C3), 130.2 9C1),
131.9/133.3 9C4a and C8a), 167.7 92£CO).
1.1.2. Preparation of enol ethers from 1-acyl-1H-cyclo-
propa[b]naphthalenes. To a stirred solution of the 1-acyl-
1H-cyclopropa[b]naphthalene
9100±150 mg,
0.41±
0.61 mmol) in anhydrous THF 915 ml) at 2788C under
argon was added BuLi 92.5 M, 0.16±0.25 ml, 1 mol
equiv.). The dark mixture was stirred at this temperature
for 30 min prior to the dropwise addition of alkyl halide
91 mol equiv.). The mixture was warmed to ambient
temperature overnight, poured into Et2O/H2O 91:1;
100 ml) and the phases separated. The aqueous phase was
extracted 9ether, 3£15 ml) and the combined organic layers
were washed 9H2O, 50 ml), dried 9MgSO4) and concentrated
under reduced pressure to a thick yellow oil which was
puri®ed by radial chromatography.
9a) From 1015 9100 mg, 0.41 mmol) after 40 h was obtained
2-phenylnaphtho[2,3-b]furan -26) 93.8 mg, 4%Ðsee
below) as a white solid from radial chromatography 9light
petroleum elution). Further elution 9dichloromethane)
gave 2--3-chloro-2-naphthalenyl)-1-phenylethanone -13)
990 mg, 79%) as a white solid and the major component; an
analytical sample was obtained 9THF) as lustrous, ¯uffy
white needles, mp 164±1668C 9Found: C, 76.8; H, 4.6; Cl,
12.6; [M1H]1 281.0728. C18H13ClO requires: C, 77.0; H,
4.7; Cl, 12.6%; [M1H]1 281.0739). nmax 3055, 3034, 3025,
1694, 1319, 1209, 976, 764, 750, 687 cm21. lmax 9MeCN)
229 94.80), 250 sh 94.26), 271 93.84), 280 93.82), 290 nm
9log e 3.62). 1H N MRd 4.59 9s, CH2), 7.44±7.54 9m, H6/7
and H13/15), 7.59±7.64 9app tt, Jˆ7.3, 1.7 Hz, H14), 7.74
9bs, H1), 7.75±7.79 9m, H5/8), 7.93 9bs, H4), 8.08±8.12 9m,
H12/16); 13C N MRd 43.5 9CH2), 126.3/126.6 9C6 and C7),
126.7/127.5 9C5 and C8), 127.6 9C4), 128.4 9C12/16), 128.7
9C13/15), 130.6 9C1), 131.0 9q), 132.0 9q), 132.3 9q),
133.295) 9q), 133.392) 9C14), 136.5 9C11), 196.6 9CO).
9a) From 1-benzoyl-1H-cyclopropa[b]naphthalene 910)15
9120/150 mg, 0.49/0.61 mmol): 9i) with trimethylsilyl
chloride 90.08 ml, 0.61 mmol) was obtained a bright yellow
solid 984 mg) after radial chromatography 9dichloro-
methane/light petroleum, 1:1) that contained 91H N MR)1-
[-trimethylsiloxy)phenylmethylidene]-1H-cyclopropa[b]-
naphthalene -18) and unchanged 10 in a 17:3 ratio.
Attempts to obtain the pure compound resulted in its decom-
position. Partial NMR data for 18 abstracted from spectra
are: 1H N MRd 0.55 9s, Me3Si), 7.30±7.31 9d, J,1 Hz, 1H),
7.37±7.43 9app tt, Jˆ7.3, 1.7 Hz, 1H), 7.41±7.42 9d,
J,1 Hz, 1H), 7.47±7.50 9BB0, 2H), 7.51±7.57 9app t,
Jˆ7.6 Hz, 2H), 7.84±7.89 9AA0, 2H), 8.05±8.09 9app d,
Jˆ8.5 Hz, 2H); 13C N MRd 0.90 9Me3Si), 96.0 9q), 104.2
9CH), 104.9 9CH), 124.7 92£CH), 127.0 9CH), 126.2
9CH), 127.8 9CH), 128.195) 9CH), 128.296) 9CH), 128.3
92£CH).
9b) From 1115 957 mg, 0.31 mmol) after 36 h was obtained
1--3-chloro-2-naphthalenyl)propan-2-one -14) 941 mg,
60%) as a pale yellow solid from radial chromatography
9dichloromethane/light petroleum elution, 1:1). An analyti-
cal sample was obtained 9same solvent mixture) as colour-
less plates, mp 87±888C 9Found: C, 71.5; H, 5.1; [M1H]1
219.0571. C13H11OCl requires: C, 71.4; H 5.1%; [M1H]1
219.0571). nmax 3045, 2922, 2903, 2853, 1721, 1588, 1492,
1402, 1361, 1334, 1319, 1165, 1135, 1006, 966, 888,
763 cm21. lmax 9MeCN) 229 95.00), 263 93.58), 272
9ii) With t-butyldimethylsilyl chloride 993 mg, 0.61 mmol)
in THF 92 ml) was obtained 1-[-t-butyldimethylsiloxy)-
phenylmethylidene]-1H-cyclopropa[b]naphthalene -19)

3534
B. Halton et al. / Tetrahedron 57 22001) 3529±3536
9125 mg, 57%) as a bright yellow solid from radial chroma-
tography 9dichloromethane/light petroleum, 1:4). An
analytical sample was obtained as bright yellow plates
from dichloromethane/light petroleum 91:1), mp 104±
1068C 9Found: C, 80.5; H, 7.295); [M1H]1 9APCI)
359.1826. C24H26OSi requires: C, 80.4; H, 7.4%; [M1H]1
359.1807). nmax 3041, 2948, 2925, 2854, 1785, 1592, 1549,
1509, 1487, 1419, 1311, 1292, 1251, 1177, 1160, 1138,
1074, 841, 783, 763, 747, 689, 608, 553 cm21. lmax
9hexane) 230 94.58), 246 sh 94.25), 254 94.15), 291 94.28),
368 94.07), 374 94.14), 393 94.56), 422 nm 9log e 4.82); UV
lmax 9MeCN) 230 94.56), 246 sh 94.25), 254 94.14), 291
94.26), 368 94.03), 372 94.07), 392 94.49), 420 nm 9log e
822, 748, 692, 672, 594, 476 cm21. lmax 9hexane) 230
94.73), 252 sh 94.31), 290 94.43), 3.71 sh 94.25), 392
94.63) 420 nm 9log e 4.75); UV lmax 9MeCN) 230 94.73),
252 sh 94.30), 290 94.41), 3.69 sh 94.22), 391 94.57), 418 nm
9log e 4.71). 1H N MRd 1.44 9d, 3JP±Hˆ14.7 Hz, 2£Me3C),
7.33±7.37 9app tt, Jˆ7.3, 1.2 Hz, H12), 7.42±7.47 9BB0,
H4/5), 7.48±7.54 9app t, Jˆ7.7 Hz, H11/13), 7.53 9d,
Jˆ1.7 Hz, H2 or H7), 7.65 9d, Jˆ1.7 Hz, H7 or H2),
7.85±7.89 9AA0, H3/6), 7.95±7.99 9app d, Jˆ8.5 Hz, H10/
1
14); 13C N MRd 26.7 92£Me3C), 37.2 9d, JP±Cˆ80.6 Hz,
2£Me3C), 99.9 9C1), 106.6/108.6 9C2 and C7), 124.0 9C10/
14), 126.0 9d, 4JP±Cˆ1.0 Hz, C1a or C7a), 126.393)/126.398)
4
9C4 and C5), 127.0 9d, JP±Cˆ1.0 Hz, C7a or C1a), 127.7
1
4.72). H N MRd 0.48 9s, Me2Si), 1.19 9s, Me3CSi), 7.29
9C12), 128.4 9C3 or C6), 128.6 9C11/13), 128.9 9C6 or C3),
132.4 9d, 2JP±Cˆ12.6 Hz, C8), 135.5 9d, 3JP±Cˆ4.5 Hz, C9),
138.3/138.9 9C2a and C6a); 31P N MRd 68.6.
9d, Jˆ1.5 Hz, H2 or H7), 7.37±7.42 9app tt, Jˆ7.3, 1.7 Hz,
H12), 7.40 9d, Jˆ1.5 Hz, H7 or H2), 7.45±7.50 9BB0, H4/5),
7.51±7.56 9t, Jˆ7.6 Hz, H11/13), 7.84±7.88 9AA0, H3/6),
8.07±8.10 9app d, Jˆ8.6 Hz, H10/14); 13C N MRd 23.7
9Me2Si), 18.4 9Me3C), 25.9 9Me3CSi), 95.9 9C1), 104.1/
104.9 9C2 and C7), 114.6 9C1a or C7a), 124.7 9C10/14),
126.195)/126.2 9C4 and C5), 126.4 9C7a or C1a), 127.8
9C12), 128.1/128.2 9C3 and C6), 128.3 9C11/13), 135.8
9C8), 137.1 9C9), 137.7/137.8 9C2a and C6a).
9b) From 1-acetyl-1H-cyclopropa[b]naphthalene 911)15
9100 mg, 0.55): 9i) with t-butyldimethylsilyl chloride
984 mg, 0.55 mmol) in THF 92 ml) was obtained after radial
chromatography 9dichloromethane/light petroleum elution,
1:4) a bright yellow oil 960 mg) that contained predomi-
nantly 1-[-1-t-butyldimethylsiloxy)ethylidene]-1H-cyclo-
propa[b]naphthalene -21) 9ca. 55 mg, ca. 35%). Sub-
sequent attempts to purify compound 21 resulted in its
decomposition. NMR data abstracted from the spectra of
9iii) With t-butyldiphenylsilyl chloride 90.13 ml, 0.49
mmol) was obtained from radial chromatography 9dichloro-
methane/light petroleum, 1:4) an analytical sample of 1-[-t-
butyldiphenylsiloxy)phenylmethylidene]-1H-cyclopro-
pa[b]naphthalene -20) 9150 mg, 63%) as a viscous tar
which solidi®ed after scratching, mp 134±1408C 9Found:
C, 84.595); H, 6.5; [M1H]1 9APCI) 483.2139. C34H30OSi
requires: C, 84.6; H, 6.3%; [M1H]1 483.2140). nmax 3071,
3050, 2927, 2855, 1589, 1547, 1506, 1486, 1471, 1445,
1418, 1386, 1287, 1151, 1132, 1114, 1073, 1025, 886,
1
the crude product are: H N MRd 0.37 9s, Me2Si), 1.05 9s,
Me3CSi), 2.29 9s, vCMe), 7.09/7.10 92£bs, H2 and H7),
7.38±7.41 9BB0, H4/5), 7.73±7.77 9AA0, H3/6); 13C N MRd
23.9 9Me2Si), 18.0 9Me3CSi), 22.3 9vCMe), 25.6
9Me3CSi), 95.4 9C1), 103.4/103.6 9C2/7), 125.6/125.7 9C4/
5), 127.9/128.1 9C3/6), 126.2, 128.4, 136.7, 137.3, 137.5 9all q).
9ii) With t-butyldiphenylsilyl chloride 90.143 ml, 0.55
mmol) was obtained a thick yellow tar 9150 mg) as the
828, 762, 742, 701, 620, 602, 552, 503, 490, 469 cm21
.
1
crude product of reaction. H NMR analysis indicated the
lmax 9hexane) 227 94.73), 254 sh 94.33), 282 94.23), 292
94.39), 369 94.16), 374 94.22), 394 94.64), 422 nm 9log e
4.90); lmax 9MeCN) 228 94.58), 254 sh 94.19), 282 94.09),
292 94.24), 368 94.01), 374 94.08), 393 94.47) 421 nm 9log e
4.71). 1H N MRd 1.30 9s, Me3CSi), 5.78 9d, Jˆ1.2 Hz, H2),
7.27 9d, Jˆ1.2 Hz, H7), 7.33±7.52 9m, 10H), 7.61±7.66 9bd
t, Jˆ7.7 Hz, H11/13), 7.74 9bd d, Jˆ8.1 Hz, H6), 7.99±8.03
9m, 4H), 8.27±8.31 9bd d, Jˆ7.3 Hz, H10/14); 13C N MRd
19.5 9Me3CSi), 26.5 9Me3CSi), 97.5 9C1), 103.9 9C7), 104.9
9C2), 124.6 9C10/14), 125.5 9C1a or C7a), 125.7/125.8 9C4
and C5), 126.4 9C7a or C1a), 127.7 92£CH), 127.8 9CH),
127.9 9CH), 128.2 9CH), 128.5 9C11/13), 129.8 9C18), 133.3
9C15), 134.6 9C8), 135.1 92£CH), 136.9 9C9), 137.5/137.7
9C2a and C6a).
presence of ole®n 22 from the presence of doublets 9ca.
Jˆ1 Hz) at d 5.99 9H2) and 7.04 9H7) with the shielding
caused by a phenyl group in analogy with the lowest energy
conformer of 20. Attempts to isolate this product resulted in
its decomposition.
1.1.3. Preparation of naptho[2,3-b]furans 26±28. 9a) A
solution of the requisite 1-acyl-1H-cyclopropa[b]naphtha-
lene 9100±340 mg, 0.35±1.87 mmol) was re¯uxed in dry
benzene 95 ml) under argon for 16 h. The residue obtained
by concentration to dryness was puri®ed as described.
9i) 1-Benzoyl-1H-cyclopropa[b]naphthalene 910) 9120 mg,
0.49 mmol) gave 2-phenylnaphtho[2,3-b]furan -26)
98 mg, 7%) as cream plates from radial chromatography
9light petroleum elution), mp 2048C 9sub.), 225±2338C
9sublimate vapourizes) 9Found: C, 86.8; H, 4.8; [M1H]1
245.0953. C18H12O requires: C, 88.5; H, 4.9 95)%;
[M1H]1 245.0961). nmax 3059, 3039, 1564, 1490, 1448,
1264, 1018, 902, 867, 761, 742, 719, 689, 478 cm21. lmax
9MeCN) 222 94.77), 272 94.77) 279 94.71), 330sh 94.59),
9iv) With di-t-butylchlorophosphine 90.09 ml, 0.49 mmol)
was obtained after radial chromatography 9ethyl acetate
elution) a mixture of di-t-butylphosphinic acid 8-[1-
-phenylmethylidene)-1H-cyclopropa[b]naphthalene]-O-
ether -24) together with an unidenti®ed phosphorous-
containing compound as a yellow oil. Subsequent radial
chromatography 9ethyl acetate/dichloromethane elution,
6:1) gave an analytical sample of 24 932 mg, 16%) as a
bright yellow oil which solidi®ed on standing, mp 158±
1618C 9Found: C, 76.7; H, 7.3; [M1H]1 405.1978.
C26H29O2P requires: C, 77.2; H, 7.2%; [M1H]1 405.1990).
1
340 94.64), 356sh nm 9log e 4.25). H N MRd 7.15 9d,
J,1 Hz, 1H), 7.41±7.52 9m, 5H), 7.92±7.97 9m, 5H),
8.04 9bs, 1H); 13C N MRd 100.7 9CH), 106.6 9CH) 118.5
9CH) 124.0 9CH), 124.7 9CH), 125.3 92£CH), 127.8 9CH),
127.9 9CH), 128.8 92£CH), 129.1 9CH), 130.1 9C), 130.2
9C), 130.7 9C), 131.5 9C), 153.9 9C), 158.1 9C).
nmax 3053, 2924, 2854, 1770, 1742, 1713, 1632, 1469, 1448,
1423, 1384, 1274, 1231, 1143, 1115, 1074, 1011, 939, 889,

B. Halton et al. / Tetrahedron 57 22001) 3529±3536
3535
When 10 950 mg, 0.20 mmol) was slowly heated to its melt-
Acknowledgements
ing point 91018C) the sample decomposed violently. The
cooled black residue was dissolved in acetone and ®ltered
though silica gel in a micropipette. The eluent was puri®ed
by radial chromatography 9light petroleum) to give naphtho-
furan 26 98.6 mg, 17%) identical to the sample obtained
above.
The work has received generous ®nancial support from the
Victoria University Science Faculty Leave and Grants
Committee 9B. H., C. S. J.), and the Curtis-Gordon and
VUW Alumni Scholarship Funds 9C. S. J.).
9ii) 1-Acetyl-1H-cyclopropa[b]naphthalene 911) 9340 mg,
1.87 mmol) gave 2-methylnaphtho[2,3-b]furan 927)
967 mg, 20%) from radial chromatography 9dichloro-
methane/light petroleum elution, 1:1) as a white solid, mp
73±748C 9lit.39 71±728C). 1H N MRd 2.54 9d, J,1 Hz, Me),
6.50 9t, J,1 Hz, H3), 7.43±7.47 9m, H6/7), 7.84 9bs, H9),
7.93±7.96 9m, H4 and H5/8); 13C N MRd 14.3 9Me), 102.2
9C3), 106.0 9C9), 117.4 9C4), 123.7/124.3 9C6 and C7),
127.7 96)/127.7 99) 9C5 and C8), 130.4 9C3a and C4a or
C8a), 130.8 9C8a or C4a), 154.0 9C9a), 158.1 9C2).
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N
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È
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