Access to cyclopropyl cations via carbene fragmentation

Article abstract of DOI:10.1016/j.tetlet.2004.02.046

Photolysis of cyclopropyloxychlorodiazirines affords cyclopropyloxychlorocarbenes whose fragmentations provide access to ion pairs, which feature cyclopropyl cations.

Full text of DOI:10.1016/j.tetlet.2004.02.046

Tetrahedron
Letters
Tetrahedron Letters 45 (2004) 3321–3326
Access to cyclopropyl cations via carbene fragmentation
Robert A. Moss* and Gaosheng Chu
Department of Chemistry and Chemical Biology, Rutgers, The State University of New Jersey, New Brunswick, NJ 08903, USA
Received 12 November 2003; accepted 4 February 2004
Abstract—Photolysis of cyclopropyloxychlorodiazirines affords cyclopropyloxychlorocarbenes whose fragmentations provide access
to ion pairs, which feature cyclopropyl cations.
ꢀ 2004 Elsevier Ltd. All rights reserved.
1. Introduction
tates and trans-3-chloro-1-R-propene in acetic acid;
cyclopropyl products are absent.5
Cyclopropyl cations are high energy species due to ring
strain and geometric restrictions that prevent the
attainment of the optimal 120ꢁ angle at the cationic
carbon atom (angle strain). An isodesmic calculation
places the parent cyclopropyl cation ꢀ30 kcal/mol above
the 2-propyl cation.1 Solvolyses of sec-cyclopropyl
tosylates (1) do not afford cyclopropyl products; par-
ticipation of the ring’s distal C–C bond in the solvolytic
process leads directly to allylic cation intermediates and
then to allylic products.2
However, tert-cyclopropyl diazonium ions can give
cyclopropyl products.4 Methanolysis of 6, for example,
gives 4–5% of the corresponding cyclopropyl methyl
ether, with 95–96% inversion from either diastereomeric
precursor.4 It is unlikely that cyclopropyl cations are
intermediates here; the products are mostly derived from
ring-opened allylic cations, while the small quantities of
cyclopropyl products form with inversion, suggestive of
SN2 processes.4;5
With tert-cyclopropyl tosylates (2), however, cycloprop-
yl cations may participate in solvolysis, leading to
significant yields of cyclopropyl products.3 This is
especially evident when R is a decent cation stabilizing
group such as cyclopropyl or phenyl.3 Thus, solvolysis
of 2 in aqueous ethanol (containing CaCO3 buffer)
affords both cyclopropyl (3) and ring-opened allylic (4)
products. When R ¼ cyclopropyl, the 3:4 ratio is 68.5/
31.5, whereas it reverses to 32/68 when R ¼ phenyl.3
These results are interpreted as supporting more effec-
tive stabilization of a cyclopropyl cation intermediate by
the cyclopropyl as opposed to the phenyl substituent.3
Kinetics and activation parameters are in accord with
this interpretation.3
Substitution of a more effective cation stabilizing sub-
stituent permits greater cyclopropyl cation participation
in deaminative solvolyses, leading to substantial yields
of cyclopropyl products. Thus 7 (R¼cyclopropyl)
decomposes in MeOH to yield 81.7% of the cyclopropyl
methyl ether analogous to 3, and 18.3% of the allylic
methyl ether corresponding to 4.4 There is somewhat
more preservation of the reactant cyclopropyl ring from
diazonium ion 7 (ꢀ82%) than from tosylate 2 (ꢀ68%,
with R¼cyclopropyl). Stereochemical studies with
D-labeled 7 indicate the stereorandom formation of the
product cyclopropyl methyl ether, consistent with the
intermediacy of achiral cyclopropyl cation 8.4
We have found that photolyses (or thermolyses) of
alkoxychlorodiazirines (9) generate alkoxychlorocarb-
enes (10), which fragment to ion pairs (11).6 This process
serves as a nonsolvolytic portal to carbocations (or
related ion pairs) of special structural interest; for
example, the 2-norbornyl7 or 1-norbornyl8 cations. The
Cyclopropyl cations can also be approached by deami-
native reactions.4;5 Secondary cyclopropyl diazonium
ions (e.g., 5, R¼Ph or Me) readily open to allylic ace-
fragmentation of carbenes 4 with loss of CO is analo-
þ
with loss of nitrogen,9 a correspondence that has
gous to the decomposition of diazonium ions (RN2
)
* Corresponding author. Tel.: +1-732-445-2606; fax: +1-732-445-5312;
e-mail: moss@rutchem.rutgers.edu
0040-4039/$ - see front matter ꢀ 2004 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2004.02.046

3322
R. A. Moss, G. Chu / Tetrahedron Letters 45 (2004) 3321–3326
R
R
OTs
H
OTs
R
OH(OEt)
R
CH2=CRCH2OH(OEt)
1
2
3
4
R
D
H
Me
R
+
+
+
+
N2
N2
N2
8
5
6
7
N
N
RO
Cl
..
[R+ OC Cl-]
ROCCl
9
10
11
N
O
OCNH2
Cl
13
OCCl
..
NH2+ OTf-
N
14
12
recently been documented in the menthyl and neomen-
thyl series.10 Accordingly, we envisioned photochemical
access to cyclopropyl cations via fragmentation reac-
tions of 10, where R¼cyclopropyl. Here, we report
successful tests of this concept.
pentane then gave diazirine 13. The diazirine was extracted
into the pentane phase as it formed, and was subse-
quently purified by chromatography on silica gel with
pentane elution. The pentane was then evaporated and
replaced with 1,2-dichloroethane (DCE) or CDCl3.
Diazirine 13 was characterized by 1H and 13C NMR, IR
(1541 cmꢁ1, N@N), and UV (kmax 348, 360 nm in DCE).
2. Bicyclopropyl system
Photolysis of the diazirine (k > 300 nm, A352 ¼ 1:0)
afforded chlorides 15–17, derived from the fragmenta-
tion of carbene 14, as well as small quantities of
dichloride 19 and formate 20, formed by capture14 of the
carbene by HCl or H2O, respectively (Scheme 1). The
1-Cyclopropyl-1-cyclopropanol11 was converted to the
isouronium triflate 12 with cyanamide and triflic acid in
THF(50 ꢁC, 30 h).12 Oxidation13 of 12 with 12% aque-
ous NaOCl (saturated with NaCl) in LiCl–DMSO/
CH2
hν
-CO
13
14
+
CCH2Cl
+
Cl-
Cl
18
15
(58-62%)
16
(25-29%)
+ ClCH2CH2CH
OCHCl2
19
(3-6%)
OOCH
20
17
(8-11%)
(1-2%)
Cl-
+
+
Cl-
21
22
Scheme 1.

R. A. Moss, G. Chu / Tetrahedron Letters 45 (2004) 3321–3326
3323
1
identities of 15–17 were established by H NMR, GC–
3. 1-Phenyl-1-cyclopropyl system
MS, and capillary GC (CP-Sil 5CB, dimethyl poly-
siloxane, 30 m) comparisons with authentic samples.
1-Chlorobicyclopropyl (15) was prepared by reaction of
1-cyclopropyl-1-cyclopropanol with SOCl2 in dry ether
()10 ꢁC, 30 min) in the presence of (diethylamino-
methyl)polystyrene.15 Chloride 15 was isolated in 75%
yield after chromatography on silica gel (9:1 hexane–
EtOAc), accompanied by 22% of 16 and 3% of 17. The
1H NMR spectrum of 15 was in accord with the litera-
ture description.16 Similarly, the key 1H NMR reso-
nances of (16)17 and (17)16 could be discerned in the
product mixtures from carbene 14 and from (1-cyclo-
propyl-1-cyclopropanolþSOCl2). Dichloride 19 and
formate 20 were identified by their distinctive NMR
signals at d 7.39 (CHCl2) and 8.07 (OOCH), which were
augmented when the fragmentations of 14 were carried
out with added HCl or H2O, respectively.
1-Phenyl-1-cyclopropanol19 was converted12 to the iso-
uronium triflate and the latter was oxidized13 to diaz-
irine 23, as was described above for the preparation of
1
diazirine 13. Diazirine 23 was characterized by H and
13C NMR, and IR (1541 cmꢁ1), and UV spectroscopy
(348, 360 nm in DCE). Photolysis of 23 (k > 300 nm,
A352 ¼ 1:0) in DCE or CDCl3 gave chlorides 26 and 27,
derived from the fragmentation of carbene 24 (Scheme
2). In CDCl3, ꢀ4% of the dichloride (HCl trapping
product of 24) also formed.
The identities of 26 and 27 follow from GC–MS, 1H and
13C NMR, and capillary GC comparisons with
authentic materials: 26 was prepared by the LiCl/
Pb(OAc)4 decarboxylation of 1-phenyl-1-cyclopropane-
carboxylic acid,20 whereas the allylic chloride, 27, was
synthesized by Wittig olefination of phenacyl chloride.21
The product distribution ranges shown in Scheme 1
were obtained from four experiments, with analysis by
capillary GC and 1H NMR. The formation of chlorides
15–17 is most economically rationalized via the inter-
mediacy of ion pair 18, formed upon fragmentation of
carbene 14: chloride return yields 15; opening of the
cyclopropyl cation to allylic cation 21, followed by
chloride return, gives 16; and chloride attack on a
distal carbon of the substituent cyclopropyl ring of
18, coupled with opening of that ring, leads to 17 (see
22).
The fragmentation products of carbene 24 can be
understood with reference to ion pair 25. Chloride
return provides cyclopropane 26, while ring opening to
ion pair 28, followed by collapse with chloride, affords
2-phenyl-3-chloropropene (27). The product distribu-
tion shown in Scheme 2 (26/27 ꢀ 0.41) is similar to the
corresponding cyclopropyl/allyl product ratio (0.47)
obtained from the aqueous ethanolysis of tosylate 2
(R¼Ph).3 The greater preservation of the cyclopropyl
ring, relative to ring opening, in the fragmentation of
carbene 14 (ratio ꢀ 2.2, Scheme 1) versus carbene 24
(ratio ꢀ 0.41, Scheme 2) is consistent with the previously
noted3 greater stabilization of a cyclopropyl cation by a
1-cyclopropyl as opposed to a 1-phenyl substituent.
The formation of 15 and 16 from 18 in a ratio of ꢀ2.2
resembles the ethanolysis of tosylate 2 (R ¼ cycloprop-
yl), where 3 and 4, analogues of 15 and 16, also form in a
ratio of 2.2.3 Deaminative methanolysis of 7 (R ¼
cyclopropyl) affords a higher (4.5) cyclopropyl/allyl
product ratio.4 The formation of chloride 17 from car-
bene 14 is not precedented in either solvolysis of tosylate
2 or the methanolysis of diazonium ion 7, but can be
accounted for by distal chloride attack on cation 8 (22).
We note, however, that if the fragmentation of carbene
14 admixes any radical character,18 opening of a radical
pair analogous to 18 would be expected16 to furnish 17
(as well as 16).
4. 2-Phenyl-1-methylcyclopropyl system
E-2-phenyl-1-methylcyclopropanol22 was converted12 to
the isouronium triflate, which was oxidized13 to diazirine
1
29. The latter was characterized by H and 13C NMR,
IR (1542 cmꢁ1) and UV spectroscopy (350, 369 nm in
DCE). Photolysis (k > 300 nm, A352 ¼ 1:0) of 29 in DCE
or CDCl3 gave chlorides 32–34, derived from the
Ph
Ph
O
N
O
Ph
-CO
+
Cl-
hν
DCE
C:
Ph
Cl
Cl
Cl
N
23
24
25
26
(27-30%)
CH2
+
Ph
ClCH2CPh
Cl-
27
(65-73%)
28
Scheme 2.

3324
R. A. Moss, G. Chu / Tetrahedron Letters 45 (2004) 3321–3326
Ph
Me
O
Ph
Me
Ph
Me
Cl
hν
-CO
Ph
Me
N
N
O
C:
DCE
+
Cl-
Cl
Cl
29
30
31
32
(42-46%)
Cl-
CH2
Ph
Me
Ph
+
Me
+
CHCMe
CH2Cl
Cl
Ph
35
33
(26-27%)
34
(27-30%)
CH2
Me
Me
Me
Me
Me
N2
MeOH
+
CHCMe
+
CH2OMe
MeO
38
36
37
Scheme 3.
fragmentation of carbene 30 (Scheme 3). Carbene cap-
ture products (dichloride or formate) were not observed.
5. Kinetics
The fragmentation kinetics of carbenes 14, 24, and 30
were determined by laser flash photolysis (LFP)14;29
using the pyridine ylide method30 to visualize the carb-
enes. Thus, LFP of diazirine 13 at 351 nm (25 ꢁC, DCE)
in the presence of pyridine generated a transient at
420 nm, which was assigned to the ylide formed by the
addition of carbene 14 to pyridine. A correlation of the
apparent rate constants for ylide formation, kobs (2.0–
1
Product identities were established by GC–MS, H, and
13C NMR comparisons with independently prepared
samples. Cyclopropane 32 (and its Z stereoisomer) were
synthesized by the addition of photogenerated MeCCl23
to styrene. Structure E-32 was assigned to the frag-
mentation product of carbene 30 based on its ‘high-field’
1H NMR methyl resonance (d 1.32), relative to the
lower-field resonance (d 1.77) of its Z stereoisomer.24
Vicinal phenyl groups are known to shield cis methyl
relative to trans methyl groups in cyclopropanes.25
Chloride 33 was obtained by reacting a-methyl-trans-
cinnamyl alcohol with SOCl2 in dry ether.26 Similar
treatment of 1-phenyl-2-methyl-3-propene-1-ol gave a
mixture of chlorides 33 (67%) and 34 (33%).27
4.5 · 105 sꢁ1
)
versus pyridine concentration (2.47–
6.59 M) was linear (6 points, r ¼ 0:997) with a slope of
6.02 · 104 Mꢁ1 sꢁ1, taken as the rate constant for ylide
formation, ky. The Y-intercept of the correlation is taken
as the rate constant for fragmentation30 of carbene 14,
kfrag ¼ 5:27 ꢂ 104 sꢁ1 31
.
carbenes 14, 24, and 30 appear in Table 1.
Rate constants ky and kfrag for
The fragmentation products of carbene 30 (Scheme 3)
can be understood in terms of ion pair 31. Return of
chloride affords cyclopropane 32 with retention of con-
figuration relative to the carbene. The stereochemistry of
chloride return is known to be retention in related car-
bene fragmentation reactions.28 Disrotatory ring open-
ing of the cyclopropyl cation of 31 to ion pair 35,
followed by chloride return, gives allylic chlorides 33
and 34; there is no evidence for the Z isomer of 33.
Despite the high energy of cyclopropyl cations,1;2 frag-
mentations of their cyclopropyloxychlorocarbene pro-
genitors are rapid. The fragmentation of 14 in DCE is
about 8 orders of magnitude faster than the ethanolysis
of tosylate 2 (R¼cyclopropyl),3 with both reactions
leading to comparable ion pairs. ROCCl fragmentations
are generally rapid,6 even when the imposition of cat-
ionic character on R leads to considerable strain, for
example, the fragmentation of 1-norbornyloxychloro-
carbene in DCE occurs with kfrag ¼ 3:3 ꢂ 104 sꢁ1 8
.
The extent of cyclopropyl ring preservation in the
fragmentation of 30 (44% of product 32) is much greater
than the 0.02–0.07% of cyclopropyl methyl ether prod-
ucts observed in the methanolysis of diazonium ion 36.4
In this reaction, ring opening products 37 (39.8%) and
38 (60.1%) almost completely account for the fate of 36.
Possibly, the vic-phenyl group of 31 helps to stabilize the
adjacent developing carbocation and maintain the
cyclopropyl ring.
Table 1. Absolute rate constants for carbene fragmentationa
Carbene kfrag (sꢁ1 ky (Mꢁ1 sꢁ1
)
)
14
24
30
(5.22 0.05) · 104
(2.87 0.11) · 105
(5.52 0.39) · 105
(6.23 0.21) · 104
(3.56 0.12) · 105
(2.58 0.02) · 105
a Results are mean values ( average deviation from the mean) of two
determinations.

R. A. Moss, G. Chu / Tetrahedron Letters 45 (2004) 3321–3326
3325
19. Kulinkovich, O. G.; Sviridov, S. V.; Vasilevskii, D. A.;
Pritytskaya, T. S. J. Org. Chem. 1989, 25, 2027, USSR
(Engl. Trans.).
20. Ogle, C. A.; Riley, P. A.; Dorchak, J. J.; Hubbard, J. L.
J. Org. Chem. 1988, 53, 4409.
21. Pasto, D. J.; Garves, K.; Sevenair, J. P. J. Org. Chem.
1968, 33, 2975.
22. Corey, E. J.; Rao, S. A.; Noe, C. M. J. Am. Chem. Soc.
1994, 116, 9345.
An Arrhenius study was carried out for the fragmenta-
tion of carbene 14. A correlation of ln(kfrag) versus 1=T
over the temperature range 253–303 K was linear (6
points, r ¼ 0:991) and gave Ea ¼ 2:3 kcal/mol,
log A ¼ 6:6, DS2ꢃ98 ¼ ꢁ30 e.u. The low activation energy
for fragmentation is opposed by a sizable unfavorable
entropy of activation, suggesting that there might by
significant cyclic ‘SNi’ character to the fragmentations of
these cyclopropyloxychlorocarbenes.6;32
23. Moss, R. A.; Mamantov, A. J. Am. Chem. Soc. 1970, 92,
6951.
1
24. 400 MHz H NMR of E-32 (d, CDCl3): 1.22 (t, J ¼ 7 Hz,
In conclusion, photolysis of cyclopropyloxychlorodiaz-
irines affords cyclopropyloxychlorocarbenes whose
fragmentations provide access to ion pairs that feature
cyclopropyl cations. When ‘stabilized’ by electron
releasing a substituents, these cations collapse with their
chloride counterions yielding significant quantities of
ring-preserved cyclopropyl products. Preliminary stud-
ies show that the reaction can be extended to secondary
cyclopropyloxychlorocarbenes, although with a dimin-
ished yield of carbene fragmentation and increasing
carbene capture.33;34
1H, ring CH), 1.32 (s, 3H, Me), 1.51 (m, 1H, ring CH),
2.65 (dd, J ¼ 7:2, 2.8 Hz, 1H, PhCH), 7.1–7.4 (m, 5H, Ph).
Z-32: 1.28 (m, 1H, ring CH), 1.47 (t, J ¼ 7 Hz, 1H, ring
CH), 1.77 (s, 3H, Me), 2.17 (t, J ¼ 8 Hz, PhCH), 7.15–7.35
(m, 5H, Ph).
25. Closs, G. L.; Moss, R. A. J. Am. Chem. Soc. 1964, 86, 4042.
1
26. 400 MHz H NMR of 33 (d, CDCl3): 1.93 (s, 3H, CH3);
4.12 (s, 2H, CH2Cl), 6.52 (s, 1H, vinyl CH), 7.18–7.30 (m,
5H, Ph).
1
27. 400 MHz H NMR of 34 (d, CDCl3): 1.74 (s, 3H, CH3),
5.00 (s, 1H, PhCHCl), 5.17 (s, 1H, vinyl CH), 5.48 (s, 1H,
vinyl CH), 7.2–7.3 (m, 5H, Ph).
28. (a) Moss, R. A.; Kim, H.-R. Tetrahedron Lett. 1990, 31,
4175; (b) Moss, R. A.; Balcerzak, P. J. Am. Chem. Soc.
1992, 114, 9836.
Acknowledgements
29. Moss, R. A.; Johnson, L. A.; Yan, S.; Toscano, J. P.;
Showalter, B. M. J. Am. Chem. Soc. 2000, 122, 11256.
30. (a) Jackson, J. E.; Soundararajan, N.; Platz, M. S.; Liu,
M. T. H. J. Am. Chem. Soc. 1988, 110, 5595; (b) Platz, M.
S.; Modarelli, D. A.; Morgan, S.; White, W. R.; Mullins,
M.; Celebi, S.; Toscano, J. P. Progr. React. Kinet. 1994,
19, 93.
We are grateful to the National Science Foundation for
financial support.
References and notes
31. At [pyridine] ¼ 0, fragmentation of 14 accounts for >90%
1. Radom, L.; Hariharan, P. C.; Pople, J. A.; Schleyer, P. v. R.
J. Am. Chem. Soc. 1973, 95, 6531.
2. Schleyer, P. v. R.; Sliwinski, W. F.; Van Dine, G. W.;
of the carbene; cf. (Scheme 1).
32. Likhotvorik, I. R.; Jones, M., Jr.; Yurchenko, A. G.;
Krasutsky, P. Tetrahedron Lett. 1989, 30, 5089.
€
Schollkopf, U.; Paust, J.; Fellenberger, K. J. Am. Chem.
Soc. 1972, 94, 125.
33. For example, fragmentation of trans-2-phenyl-1-cycloprop-
yloxychlorocarbene in DCE affords 12% of trans-2-
phenyl-1-chlorocyclopropane, 9% of cis-2-phenyl-1-chloro-
cyclopropane, 11% of trans-1-phenyl-3-chloro-1-propene,
19% of 3-chloro-3-phenylpropene, 41% of the dichloride
due to HCl capture of the carbene, and 8% of the formate
due to water capture of the carbene.
€
3. Salaun, J. J. Org. Chem. 1978, 43, 2809.
4. Kirmse, W.; Rode, J.; Rode, K. Chem. Ber. 1986, 119,
3672.
5. Wiberg, K. B.; Osterle, C. G. J. Org. Chem. 1999, 64, 7756.
6. Moss, R. A. Acc. Chem. Res. 1999, 32, 969.
€
ꢀ
7. Moss, R. A.; Zheng, F.; Fede, J.-M.; Ma, Y.; Sauers,
R. R.; Toscano, J. P. J. Am. Chem. Soc. 2001, 123, 8109.
34. Preparation of compounds 12 and 13. 1-Cyclopropyl-1-
cyclopropylisouronium triflate (12). In a 50 mL round
bottom flask fitted with a stirring bar and reflux condenser
protected with a calcium chloride drying tube, were placed
1.00 g (23.8 mmol) of cyanamide, 4.67 g (47.6 mmol) of
1-cyclopropyl-1-cyclopropanol,11 and 15 mL of anhydrous
THF. Then 3.57 g (23.8 mmol) of trifluoromethanesulfonic
acid in 10 mL of THFwas slowly added. The mixture was
stirred magnetically at 50 ꢁC (oil bath) for 30 h, and then
cooled to room temperature. THFwas removed on the
rotary evaporator to give a yellow oil, which was washed
three times with pentane. The oil was characterized as
triflate 12 (containing some urea) by NMR, and was used
in the next step without further purification. 3-Chloro-3-
(1-cyclopropyl-1-cyclopropyloxy)diazirine (13). Isouro-
nium salt 12 (4.5 g) and 3.50 g of LiCl were added to a
mixture of 25 mL of DMSO and 50 mL of pentane. The
mixture was stirred magnetically and cooled to 20 ꢁC.
Then 100 mL of commercial 12% aqueous sodium hypo-
chlorite solution (pool chlorine), saturated with NaCl, was
slowly added while the temperature was kept below 30 ꢁC.
After the addition was complete, stirring was continued
for 15 min at 15 ꢁC. The reaction mixture was poured into
a separatory funnel containing 150 mL of ice water. The
ꢀ
8. Moss, R. A.; Zheng, F.; Fede, J.-M.; Ma, Y.; Sauers,
R. R.; Toscano, J. P.; Showalter, B. M. J. Am. Chem. Soc.
2002, 124, 5258.
9. Skell, P. S.; Starer, I. J. Am. Chem. Soc. 1959, 81, 4117.
10. Moss, R. A.; Johnson, L. A.; Kacprzynski, M.; Sauers,
R. R. J. Org. Chem. 2003, 68, 5114.
11. de Meijere, A.; Kozhushkov, S. I.; Spaeth, T.; Zefirov,
N. S. J. Org. Chem. 1993, 58, 502.
12. Moss, R. A.; Kaczmarcyk, G. M.; Johnson, L. A. Synth.
Commun. 2000, 30, 3233.
13. Graham, W. H. J. Am. Chem. Soc. 1965, 87, 4396.
14. Moss, R. A.; Ge, C.-S.; Maksimovic, L. J. Am. Chem. Soc.
1996, 118, 9792.
15. Weber, W.; de Meijere, A. Synth. Commun. 1986, 16, 837.
16. Landgrebe, J. A.; Becker, L. W. J. Am. Chem. Soc. 1968,
90, 395, This early report focuses on the generation of
cation 8 from chloride 15.
17. Cristol, S. J.; Daughenbaugh, R. J. J. Org. Chem. 1979, 44,
3434.
18. (a) Blake, M. E.; Jones, M., Jr.; Zheng, F.; Moss, R. A.
Tetrahedron Lett. 2002, 43, 3069; (b) Moss, R. A.; Ma, Y.;
Sauers, R. R. J. Am. Chem. Soc. 2002, 124, 13968.

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R. A. Moss, G. Chu / Tetrahedron Letters 45 (2004) 3321–3326
organic phase was removed and saved, the aqueous phase
evaporation and replaced by DCE or CDCl3. Residual
pentane was then removed by rotary evaporation at 0 ꢁC.
The yield of 13 was approximately 25%, based on
1-cyclopropyl-1-cyclopropanol.
1H NMR (400 MHz, d, CDCl3): 0.2–0.9 (m, 8H, ring
CH2), 1.61–1.65 (m, 1H, CH). 13C NMR (d, CDCl3):
70.35, 65.76, 13.73, 9.82, 4.85. IR (NaCl): 1543 cmꢁ1
(diazirine). UV (kmax, DCE): 352, 361 nm.
was washed with pentane (2 · 30 mL), and then discarded.
The pentane washings were back washed with 2 · 75 mL of
ice water. Then the combined organic phases were dried
for 1 h over calcium chloride at 0 ꢁC. The pentane/diazirine
solution was purified by column chromatography over
ꢁ
200–400 mesh, 60 A silica gel, eluted with pentane. The
pentane solution of product was reduced by rotary