9,9-Dimethyl-8,10-dioxapentacyclo[5.3.0.02,5.0 3,5.03,6]decane and naphthotetracyclo[5.1.0.0 1,6.02,7]oct-3-ene: New substituted [1.1.1]propellanes as precursors to 1,2,3,4-tetrafunctionalized bicyclo

Article abstract of DOI:10.1016/j.tet.2004.10.057

Two new substituted [1.1.1]propellanes have been generated from the corresponding bicyclo[1.1.0]butanes in either single-step (1a) or four-step procedures (1b). The observed degree of double lithiation of the bicyclo[1.1.0]butanes is discussed in the cont

Full text of DOI:10.1016/j.tet.2004.10.057

Tetrahedron 61 (2005) 89–95
9,9-Dimethyl-8,10-dioxapentacyclo[5.3.0.02,5.03,5.03,6]decane
and naphthotetracyclo[5.1.0.01,6.02,7]oct-3-ene: new
substituted [1.1.1]propellanes as precursors to
1,2,3,4-tetrafunctionalized bicyclo[1.1.1]pentanes
†
*
Baldur Stulgies, Dennis P. Pigg, Jr., Piotr Kaszynski and Zbigniew H. Kudzin
Organic Materials Research Group, Department of Chemistry, Vanderbilt University, Box 1822, Station B, Nashville, TN 37235, USA
Received 21 September 2004; revised 19 October 2004; accepted 20 October 2004
Available online 11 November 2004
Abstract—Two new substituted [1.1.1]propellanes have been generated from the corresponding bicyclo[1.1.0]butanes in either single-step
(1a) or four-step procedures (1b). The observed degree of double lithiation of the bicyclo[1.1.0]butanes is discussed in the context of DFT
computational results. Addition reactions across the central C(1)–C(3) bonds of the propellanes were studied. Only the propellane 1b gave
the biacetyl addition product.
q 2004 Elsevier Ltd. All rights reserved.
1. Introduction
Polyfunctionalized bicyclo[1.1.1]pentanes (BCPs)1 bearing
functional substituents in addition to the two bridgehead
ones are rare and sought-after as potential structural
elements for molecular electronics and architecture.2–4
Figure 1. Retrosynthetic analysis for preparation of 1,2,3,4-tetrafunction-
alized bicyclo[1.1.1]pentanes A through propellanes B.
Among a handful of such derivatives are 2,2-dichloro-5
and polyfluoro derivatives,6,7 which were obtained by direct
propellane11 introduces a carbonyl group amenable to
halogenation of bicyclo[1.1.1]pentane-1,3-dicarboxylic
further functional group manipulation.12–14
acid or its esters.8 Further transformations of the halogens
to other groups have not been successful. In contrast,
transformations of the carboxyl groups proceeded
smoothly,7,9 which enable the generation of 2,2-
dichloro[1.1.1]propellane.9 Recently, chlorination of the
2,4-dimethylene derivative of bicyclo[1.1.1]pentane-1,3-
dicarboxylic acid and subsequent transformations of the
halogenated products led to bicyclo[1.1.1]pentane-1,2,3,4-
tetracarboxylic acid, the first example of tetrafunctionalized
BCP A.10
Most [1.1.1]propellanes prepared to date are mono or
geminally disubstituted derivatives of the parent [1.1.1]pro-
pellane or its 2,4-dimethylene or 2,4-trimethylene deriva-
tives.1,15 Only a handful of [1.1.1]propellanes are
substituted with aryl,16–18 vinyl18 or alkoxymethyl19,20
groups which are inert to propellane generation conditions
and can be converted to the versatile carboxyl group. To
our knowledge there is only one propellane with a benzyl
group bridging the 2 and 4 positions,16 which is a
potential precursor to 1,2,3,4-tetrafuctionalized BCPs A.
Unfortunately, the chemistry of this propellane has not been
investigated.
A more versatile and general approach to polyfunction-
alized BCPs A may, in principle, involve appropriately
substituted [1.1.1]propellanes B (Fig. 1). Subsequent
addition of biacetyl across the central bond of the
Keywords: Substituted bicyclo[1.1.0]butanes and [1.1.1]propellanes;
Theoretical models; Radical reactions.
* Corresponding author. Tel.: C1 615 322 3458; fax: C1 615 343 1234;
e-mail: piotr.kaszynski@vanderbilt.edu
† On leave from University of Lodz, Poland.
0040–4020/$ - see front matter q 2004 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2004.10.057

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B. Stulgies et al. / Tetrahedron 61 (2005) 89–95
In order to develop synthetic access to tetrafunctionalized
BCPs A, we focused on two new propellanes 1a and 1b.
Here, we report the generation of the two substituted
propellanes and some reactions at the central C–C bond with
the emphases on the addition of biacetyl.
decomposition of the precursor 2b. This necessitated the use
of the four-step route16 shown in Scheme 2. Thus,
hydroxymethylation of 2b gave alcohol 3b as a mixture of
two isomers in about 2:1 ratio contaminated with a more
polar compound presumably the corresponding
bis(hydroxymethyl) derivative. After purification on
alumina, the isomeric mixture of alcohols 3b was
brominated and the resulting 4b was subsequently converted
to the dihalide 5b using the general literature conditions.16
To improve the separation of the pure 5b, small amounts of
EtOH were added in the end of the reaction to convert the
residual Ph3P to the oxide. The overall average yield for the
three steps was about 25%.
2. Results and discussion
2.1. Preparation of propellanes
Propellanes 1a and 1b were prepared from appropriate
bicyclo[1.1.0]butanes 2a and 2b using the methodology
developed by Szeimies.16 The former propellane was
prepared in a single annelation step with ClCH2I taking
advantage of the almost quantitative double deprotonation
of 2a (Scheme 1). The propellane 1a was prepared in yields
estimated at 30–40% and used as crude solutions in
subsequent reactions.
To assign stereochemistry of the two isomers formed during
hydroxymethylation of 2b, the minor isomer of 3b was
isolated chromatographically and the solid alcohol was
purified by sublimation. NOESY experiments were incon-
clusive and the stereochemistry of the isomers was assigned
based on a comparison of computational and experimental
NMR data (Fig. 2). The analysis shows that the differences
in theoretical chemical shifts Dd (theor) for the anti and syn
isomers follows the trend in the differences in experimental
chemical shifts Dd (exp) between the minor and major
isomers. Perhaps the most diagnostic are the bridgehead
positions of the bicyclo[1.1.0]butane ring and the hydroxy-
methyl group, which are most affected by the structural
variation in the two isomers. Thus, the bridgehead carbon
atom C(3) is significantly shielded, while C(4) is deshielded
in the major and syn isomers relative to the minor and anti.
Also, the CH2 protons are significantly deshielded and the
13C nucleus is shielded in the major and syn isomers relative
to the minor and anti. This is consistent with general trends
in exo/endo stereoisomers of bicycloalkanes.
Scheme 1.
In contrast, propellane 1b could not be prepared in the
single-step procedure since the double deprotonation of 2b
was inefficient. Using n-BuLi, sec-BuLi or tert-BuLi at
different temperatures, the double deprotonation occurred to
less than 20%, as determined by quenching with D2O and
GCMS analysis.21 Also prolonged reaction times led to
Scheme 2.
Figure 2. Optimized gas phase geometries for 3b-anti and 3b-syn isomers and comparison of the difference in experimental and computed NMR chemical
shifts: Dd (exp)Zd (3b-minor)Kd (3b-major); Dd (theor)Zd (3b-anti)Kd (3b-syn). Theoretical results obtained at the B3LYP/6-31G(d,p) level of theory.

B. Stulgies et al. / Tetrahedron 61 (2005) 89–95
91
0.6 ppm relative to that in the parent [1.1.1]propellane.16
For comparison, the CH2 group in 1a is shielded by about
0.25 ppm.
The bicyclo[1.1.0]butane 2a was prepared from 1H-
phenalene (6), obtained by dehydration of 2,3-dihydro-1H-
phenalen-1-ol23 (7), following closely the literature pro-
cedure.24 The alcohol 7 was conveniently prepared from
2,3-dihydro-1H-phenalen-1-one by substituting NaBH4 for
LiAlH4 used in the original procedure25 (Scheme 3).
Bicyclo[1.1.0]butane 2b was prepared from benzvalene in
two steps and 35% average overall yield (Scheme 4). Thus,
2b was obtained by the reaction of glycol26,27 8 with 2,2-
dimethoxypropane in the presence of TsOH for 30 min at
0 8C. Benzoic acid in benzene used in a similar procedure26
was found to be ineffective in the present case. The
preparation of benzvalene followed a literature procedure28
except that a larger than recommended amount of MeLi was
used in the third part of the reaction. When the second
portion of MeLi was stoichiometric relative to CH2Cl2, the
yields of benzvalene established by NMR29 were 36–57%
and similar to those reported in the literature.28
Scheme 3.
Scheme 4.
Thus, the comparison indicates that the major isomer of 3b
has syn stereochemistry. This conclusion, however, is in
contrast with previous reports on regioselectivity of
methylation of a related carbocyclic system, where
configuration of the major product was established to be
anti based on independent synthesis.22 Perhaps the domi-
nance of the syn isomer in the present case results from the
complexing ability of the 1,3-dioxolane ring oxygen atoms
and preferential deprotonation of the pro-syn position.
2.2. Molecular geometry and strain of 1 and 2
Structural effects on molecular geometry and strain
energy of the parent [1.1.1]propellane (1c) and
bicyclo[1.1.0]butane (2c) rings in 1 and 2 were assessed at
the B3LYP/6-31G(d,p) level of theory and results are
collected in Table 1. Analysis shows that the central C(1)–
C(3) bond has virtually the same length in all three
propellanes 1, while in bicyclo[1.1.0]butanes 2a and 2b is
Propellane 1b was generated by treatment of a mixture of
stereoisomers 5b with MeLi and used as crude Et2O/pentane
solutions without further purification. 1H NMR of 1b shows
that the propellane CH2 group is deshielded by about
˚
shorter by about 0.02 A than in the parent 2c. The latter is
A
consistent with experimental results for 2a30 and 2c.31
comparison of the angles a indicates a modest contraction of
Table 1. Selected structural parameters and strain energies of propellanes 1 and bicyclo[1.1.0]butanes 2
aa (deg)
bb (deg)
SEc (kcal/mol)
˚
dC1–C3 (A)
1
a
b
1.576
1.576
1.578
118.6
112.4
120.0
124.3
112.2
122.6
94
92.5
98
c, RZH
1.596(5)d
98e
2
a
1.471
1.47(3)f
1.472
1.491
1.497(3)g
118.0
120(2)f
110.9
121.9
122.7(5)g
124.6
124(2)f
113.0
124.7
121.6(9)g
62
b
60
66
c, RZH
64e
a Angle between the two cyclopropane rings defined as C(2)-*-C(4), where * is the C(1)–C(3) midpoint.
b Angle defined as R-C(2)-*, where * is the C(1)–C(3) midpoint.
c Homodesmotic strain energies (SE) calculated according to Figure 3.
d Electron diffraction data; Hedberg, L.; Hedberg, K. J. Am. Chem. Soc. 1985, 107, 7257–7260.
e Ref 31.
f
Solid state data; Ref. 30.
g Infrared data; Ref. 31.

92
B. Stulgies et al. / Tetrahedron 61 (2005) 89–95
Figure 3. Homodesmotic reactions. Strain energies are listed in Table 1.
the angle between the cyclopropyl faces in the naphthalene
derivatives 1a and 2a relative to the parent systems 1c and
2c. In contrast, the angle a in the dioxolane derivatives is
smaller by about 78 for 1b and 118 for 2b, relative to the
parent hydrocarbons. Similar results are obtained for the
exocyclic bond angle b, which indicates a generally larger
distortion of the propellane and bicyclobutane rings in the
dioxolane (b) than in the naphthalene (a) derivatives.
enhanced C–H acidity of the bridgehead positions in the
former and a more facile double deprotonation than in 2a.
For comparison, in the parent BCB the exocyclic orbital is
sp1.93 hybridized. Thus, the origin of the problem with the
double deprotonation of 2b is not clear.
2.3. Reaction of propellanes 1
Initially, we investigated addition reactions to 1a. Unfortu-
nately, no radical or photochemical addition to this
propellane gave a characterizable product (Scheme 5).
Thus, the photochemically-induced addition of biacetyl11 to
1a in cyclohexane gave only highly colored decomposition
products, even when a uranium glass filter was used to limit
excitation of the naphthalene ring.34 The colored products
presumably resulted from the light-induced rearrangement
of 1a and subsequent polymerization of the olefins.35
Addition of I2 to 1a in ether36 resulted only in a black tar.
Similarly, radical addition of PhSH or PhSSPh36 to 1a in
ether at ambient temperature led to a brown complex
mixture of unidentified products. Finally, attempts to
introduce a carboxyl group at the bridgehead positions in
1a first by lithiation either with t-BuLi37 or lithium 4,40-di-t-
butylbiphenyl13 followed by carboxylation with CO2 was
unsuccessful, and only a complex mixture of products was
obtained.
In spite of significant deformation of the parent rings in the
ketal derivatives 1b and 2b, the strain energies (SE) calculated
using homodesmotic reactions32 shown in Figure 3 are similar
(within 6 kcal/mol) to those calculated in this work and
previously reported33 for the parent hydrocarbons.
The theoretical models for 1 and 2 provide an opportunity to
analyze factors that may affect the efficiency of the double
deprotonation of 2a and 2b. Previous studies concluded that
a high degree of lithiation occurs for bicyclo[1.1.0]butanes
carrying an sp2 substituent, such as a phenyl ring, or those
having a small angle between the cyclopropane faces.21
Thus, the ease of double deprotonation of 2a is in agreement
with these empirical observations. In contrast, the low
efficiency of complete deprotonation of 2b is inconsistent
with the previous conclusions and the 95% of double
deprotonation observed21 for 2,4-dimethylenebicyclo-
[1.1.0]butane (tricyclo[3.1.0.02,6]hexane), a close analog
of 2b; both compounds have very similar small angle a of
about 1118. Also, the computational analysis of the
electronic structure of the bicyclobutanes is inconsistent
with the deprotonation results. The NBO population
analysis shows that the hybridization of the C(1/3) exocyclic
hybrid is sp1.81 in 2b which has more s-character than the
analogous orbital found in 2a (sp1.90). This would suggest
Scheme 5.

B. Stulgies et al. / Tetrahedron 61 (2005) 89–95
93
In contrast, propellane 1b underwent a smooth addition of
biacetyl to form the diketone 9 in good yield (Scheme 6).
The pure diketone 9 was separated from other by-products
using column chromatography. The formation of polar by-
products is promoted by large amounts of ether used as
solvent, presumably due to light-induced radical reactions
between biacetyl, ether and propellane.
unless specified otherwise. Chemical shifts were referenced
to TMS (1H) or solvent (13C). IR spectra were recorded for
neat samples on NaCl plates. Mass spectrometry data were
acquired using a GCMS instrument. FAB/HRMS spec-
trometry was performed at Notre Dame University, IN.
Elemental Analysis was provided by Atlantic Microlabs,
GA. All reactions with organometallic reagents were
performed under nitrogen and strictly anhydrous conditions.
In these cases the glassware used was heated in vacuo to
remove all residual moisture. All workup operations with
propellanes 1a and 1b were performed in an inert
atmosphere.
5.1.1. Naphthotetracyclo[5.1.0.01,6.02,7]oct-3-ene (1a). To
a solution of the bicyclobutane24 2a (145 mg, 0.814 mmol)
in Et2O (10 mL), n-BuLi solution in hexane (0.74 mL,
1.79 mmol, 2.44 M) was added at ambient temp and stirred
for 6 h. The reaction mixture was cooled to K30 8C and
chloroiodomethane (174 mg, 0.984 mmol) was added drop-
wise and stirred for 2 h at ambient temp. Then a 2 N aqueous
NH3 (5 mL) was added at 0 8C and stirred for 25 min. The
aqueous layer was extracted with benzene (2!8 mL), the
combined organic layers were dried (Na2SO4), and
concentrated at reduced pressure. In case of visible
precipitation, the solution can be filtered through a
microfilter to remove polymeric materials. The resulting
Scheme 6.
3. Summary and conclusions
The preparation of both propellanes 1a and 1b was
accomplished in about 5% overall yield starting from
commercial 1-chloromethylnaphthalene (for 1a) and cyclo-
pentadiene (for 1b) and using demanding seven-step
procedures. Of the two propellanes, only 1b proved useful
for the formation of tetrasubstituted bicyclo[1.1.1]pentanes,
and the diketone 9 was obtained in high yield from 1b. In
contrast, neither the photochemically- or thermally-induced
radical additions to the central C(1)–C(3) bond in 1a, nor a
reaction with organometallic reagents led to isolable
bicyclo[1.1.1]pentane derivatives.
1
solid 1a was about 90% pure by NMR: H NMR (C6D6)
major signals d 1.81 (s, 2H), 3.57 (s, 2H), 6.86 (d, JZ
6.8 Hz, 2H), 7.06 (dd, J1Z8.4 Hz, J2Z6.8 Hz, 2H), 7.37 (d,
JZ8.4 Hz, 2H). The crude solid propellane was dissolved in
an appropriate solvent and used in subsequent reactions.
The stereochemistry of the main isomer formed in
hydroxymethylation of bicyclobutane 2b was assigned as
syn based on the comparison of experimental and theoretical
chemical shifts for the syn and anti isomers. Simple analyses
of molecular geometry and the hybridization of the C(1/3)
exocyclic bond orbital in bicyclo[1.1.0]butanes 2a and 2b
could not explain the observed marked difference in their
ability to form dianions.
5.1.2. 9,9-Dimethyl-8,10-dioxapentacyclo[5.3.0.02,5
.03,5.03,6]decane (1b). To a solution of dihalide 5b
(231 mg, 0.83 mmol) in Et2O/pentane (15 mL, 2:1), MeLi
in Et2O (1.6 M, 0.62 mL, 0.99 mmol) was added at K30 8C
and stirred for 2 h at ambient temp. Then a 2 N aqueous NH3
(10 mL) was added at 0 8C and stirred for 20 min. The
aqueous layer was extracted with Et2O (2!10 mL) and the
combined organic layers were dried (Na2SO4). The resulting
solution of propellane 1b was used directly for the next
transformation to form 9: 1H NMR (ether/pentane/CDCl3) d
2.64 (s, 2H), 2.66 (s, 2H), 4.64 (s, 2H), the Me groups
are obscured by the solvent peaks; MS, m/z (%) 163 (1)
[MKH]C, 149 (100) [MKCH3]C.
Thus, propellane 1b is a promising precursor to 1,2,3,4-
tetrafunctionalized bicyclo[1.1.1]pentanes. The functional
group transformations of diketone 9 will be reported
elsewhere.
4. Computational details
5.1.3. 8,8-Dimethyl-7,9-dioxatetracyclo[4.3.0.02,4.03,5]no-
nane (2b). To a solution of the diol 8 (16.2 g, 145 mmol)
and 2,2-dimethoxypropane (500 mL) in CHCl3 (500 mL),
p-TsOH$H2O (350 mg, 1.84 mmol) was added at K5 to
0 8C and the mixture was stirred for 30 min at the
temperature below 0 8C. The reaction mixture was diluted
with CHCl3 (500 mL), washed with NaHCO3 (2!300 mL)
and brine (300 mL), dried (Na2SO4) and volatiles were
removed under reduced pressure. Kugelrohr distillation (bp
40–44 8C/0.4–0.5 Torr) gave 19.9 g (90% yield) of the
acetonide 2b as a colorless low melting solid. For other four
runs in 4–150 mmol scale the yields were 70–89%. Mp 19–
All quantum-mechanical calculations were carried out at the
B3LYP/6-31G(d,p) level of theory38,39 using the Linda–
Gaussian 98 package40 on a Beowulf cluster of 16
processors. Geometry optimizations were undertaken
using appropriate symmetry constraints and default
convergence limits. The isotropic shielding factors were
obtained by using the GIAO algorithm.
5. Experimental
5.1. General
1
21 8C; H NMR d 1.28 (s, 3H), 1.47 (s, 3H), 2.02 (dt, J1Z
8.4 Hz, J2Z2.0 Hz, 1H), 2.29 (br s, 2H), 2.33–2.38 (m, 1H),
4.49 (br s, 2H); 13C NMR d 2.9, 8.6, 25.4, 26.9, 37.6, 82.4,
114.1; MS, m/z (%) 152 (2) [M]C, 137 (100); HRMS, calcd
1
Melting points are uncorrected. H and 13C NMR spectra
were obtained at 300 and 75 MHz, respectively, in CDCl3,

94
B. Stulgies et al. / Tetrahedron 61 (2005) 89–95
for C9H11O2: 151.0759, found 151.0763. Anal. Calcd for
C9H12O2: C, 71.03; H, 7.95. Found: C, 70.51: H, 7.62.
solution was concentrated and the residue sublimed to give
1.19 g (66% yield) of 5b as a white solid. For other four runsin
1–14 mmol scale the yields were 58–67%. Mp 55–65 8C; 1H
NMR d major/minor 1.27/1.25 (s, 3H), 1.49/1.45 (s, 3H), 2.72/
2.73 (s, 2H), 4.05/4.30 (s, 2H), 4.58/4.62 (s, 2H); 13C NMR d
major/minor 22.7/22.9, 25.5/24.9, 27.0/26.7, 29.6/25.3, 40.0/
39.4, 47.2, 82.2/81.7, 115.0/114.5; MS, m/z (%) 280/278 (3/2)
[M]C, 265/263 (10/8) [MKCH3]C, 77 (100). Anal. Calcd for
C10H12BrClO2: C, 42.96; H 4.33. Found: C, 43.19; H, 4.39.
5.1.4. 8,8-Dimethyl-7,9-dioxatetracyclo[4.3.0.02,4.03,5]no-
nan-3-ylmethanol (3b). To a solution of the bicyclobutane
2b (6.00 g, 39.4 mmol) in Et2O (50 mL), n-BuLi solution in
hexane (18.5 mL, 43.4 mmol, 2.35 M) was added at ambient
temperature and stirred for 4 h. Gaseous formaldehyde,
prepared by depolymerization of paraformaldehyde (6.00 g)
at 170 8C, was introduced into the reaction mixture. After
additional stirring for 1 h, water (25 mL) was added at ice
bath cooling. The organic layer was washed with water (3!
10 mL) and the combined aqueous phases were extracted
with ether (2!10 mL). The organic layer was dried
(Na2SO4) and concentrated in vacuo. Column chromato-
graphy (Al2O3, Grade IV; CH2Cl2/MeOH 19:1 ratio
containing 1% Et3N, RfZ0.35) gave 4.09 g (57% yield) of
alcohol 3b as a 2:1 mixture of regio-isomers. For other four
runs in 2–50 mmol scale the yields were 40–60%. The
minor isomer was isolated as a slightly less polar fraction in
the chromatographic purification of the mixture.
5.1.7. 2,3-Dihydro-1H-phenalen-1-ol.25 (7) 2,3-Dihydro-
1H-phenalen-1-one42 (3.64 g, 20.0 mmol) was added in one
portion to a solution of NaBH4 (984 mg, 26.0 mmol) in
MeOH (50 mL) at 0 8C. The reaction mixture was stirred for
24 h at ambient temperature and quenched with 5% aq HCl
(5 mL) and H2O (200 mL). The precipitate was filtered and
dissolved in Et2O (80 mL). The organic phase was washed
with H2O (10 mL), dried (Na2SO4) and concentrated to
yield the crude product. Flash column chromatography
(SiO2 3.5!30 cm, CH2Cl2, RfZ0.35) gave 3.17 g (86%
yield) of alcohol 7 as an off-white light-sensitive solid: mp
81–83 8C (lit.25 85–86 8C); 1H NMR d 1.89 (br s, 1H), 2.09–
2.26 (m, 2H), 3.07 (dt, J1Z16.4 Hz, J2Z5.9 Hz, 1H), 3.31
(ddd, J1Z16.4 Hz, J2Z8.2 Hz, J3Z5.4 Hz, 1H), 7.29 (dd,
J1Z6.8 Hz, J2Z0.7 Hz, 1H), 7.39 (dd, J1Z7.7 Hz, J2Z
6.8 Hz, 1H), 7.45 (dd, J1Z7.7 Hz, J2Z7.1 Hz, 1H), 7.54 (d,
JZ7.1 Hz, 1H), 7.69 (d, JZ7.7 Hz, 1H), 7.78 (d, JZ
7.1 Hz, J2Z0.9 Hz, 1H).
Minor isomer (3b-anti): mp 60.5–62 8C; 1H NMR d 1.26 (s,
3H), 1.45 (s, 3H), 2.42 (br s, 1H), 2.43 (s, 2H), 4.04 (s, 2H),
4.54 (s, 2H); 13C NMR d 7.0, 24.7, 25.3, 26.8, 40.7, 59.5,
82.1, 113.9; IR 3400 (br, OH), 1212 (C–O) cmK1; GC/MS,
rt 11.6 min, m/z (%) 182 (2) [M]C, 167 (23) [MKCH3]C,
107 (55), 95 (100). Anal. Calcd for C10H14O3: C, 65.91; H
7.74. Found: C, 65.79; H, 7.79.
5.1.8. 3,5-Diacetyl-9,9-dimethyl-8,10-dioxatetracyclo-
[5.3.0.02,5.03,6]decane (9). Freshly distilled 2,3-butanedione
(2 mL) was added to a solution of propellane 1b in Et2O/
pentane prepared from 231 mg (0.83 mmol) of dihalide 5b.
The mixture was stirred at about 5 8C and irradiated with a
450 W medium-pressure Hanovia mercury lamp for 5 h.
Volatiles were removed and the residue was short-path
distilled (110 8C/0.01 Torr) giving 175 mg (85% based on
5b) of hygroscopic diketone 9. Alternatively, diketone was
purified by column chromatography (neutral Alumina,
Grade 1, hexane/CH2Cl2 9:1). For other three runs in
0.5–3 mmol scale the yields were 50–68% based on 5b. 1H
NMR d 1.28 (s, 6H), 2.08 (s, 3H), 2.21 (s, 3H), 2.42 (s, 2H),
3.33 (t, JZ0.8 Hz, 2H), 4.85 (t, JZ0.8 Hz, 2H); 13C NMR d
24.1, 24.3, 27.0, 27.4, 43.1, 47.7, 55.2, 65.0, 81.1, 114.7,
204.4; MS, m/z (%) 235 (100) [MKCH3]C; HRMS, calcd
for C14H19O4: 251.1283, found 251.1286.
Major isomer (3b-syn) assigned from the mixture: 1H NMR
d 1.25 (s, 3H), 1.44 (s, 3H), 2.19 (br s, 1H), 2.37 (s, 2H), 4.24
(s, 2H), 4.48 (s, 2H); 13C NMR d 13.5, 18.9, 25.1, 27.0, 40.6,
58.6, 82.6, 114.3; GC/MS, rt 10.9 min, m/z (%) 182 (1)
[M]C, 167 (100) [MKCH3]C, 95 (55).
5.1.5. 4-Bromo-8,8-dimethyl-7,9-dioxatetracyclo[4.3.
0.02,4.03,5]nonan-3-ylmethanol (4b). To a solution of the
isomeric mixture of alcohols 3b (1.79 g, 9.83 mmol) in Et2O
(10 mL), n-BuLi solution in hexane (10 mL, 23.0 mmol,
2.3 M) was added and the mixture was stirred for 5 h. Solid
p-toluenesulfonyl bromide41 (2.70 g, 11.6 mmol) was added
at 0 8C and the mixture was stirred for 1 h at ambient
temperature. Then 10% NaOH (5 mL) was added dropwise.
The aqueous layer was washed with Et2O (3!20 mL), the
combined organic layers were dried (Na2SO4) and concen-
trated in vacuo to give 2.23 g (87% yield) of 85% pure
(GCMS) 4b as a yellowish oil, which was used without
further purification for the next transformation. For other
Acknowledgements
1
four runs in 1–15 mmol scale the yields were 60–82%. H
NMR d (major signals) 1.26 (s, 3H), 1.44 (s, 3H), 2.67 (br s,
2H), 4.36 (br s, 2H), 4.62 (br s, 2H); MS, m/z (%) 260/262
(10/8) [M]C, 187/185 (38/42), 67 (100); HRMS, calcd for
C10H13BrO3: 260.0048, found 260.0051.
Financial support for this work was received from the
Petroleum Research Fund (37174-AC1).
5.1.6. 3-Bromo-4-(chloromethyl)-8,8-dimethyl-7,9-dioxa-
tetracyclo[4.3.0.02,4.03,5]nonane (5b). A solution of crude
bromo alcohol 4b (1.69 g, 6.47 mmol) and Ph3P (3.54 g,
13.5 mmol) in CCl4 (35 mL) was stirred for 10 h at 80 8C.
EtOH (2 mL) was added and stirring was continued for
additional 3 h. After cooling, Celite (w5 g) was added and the
mixture concentrated in vacuo. The solid residue was washed
with petroleum ether containing CH2Cl2 (10%), the resulting
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