Photoreactions of γ,δ-unsaturated chromium carbene complexes

Article abstract of DOI:10.1021/ja9537585

A number of functionalized γ,δ-unsaturated chromium carbene complexes were synthesized, and their photochemistry was studied. Photolysis of carbene complexes 5 and 17 induced intramolecular [2 + 2] cycloaddition to afford cyclobutanones 6 and 18, respectively. If the photoreactions were not run in thoroughly degassed solvents, small amounts of lactones 7 and 19 were obtained as well. Cyclobutanones 6 and 18 were stable once isolated, but underwent an acid-catalyzed Pinacol rearrangement/hydrolysis transformation in acidic solution to afford novel α-hydroxy-substituted bicyclo[3.1.0]hexanone compounds 20 and 21. Photolysis of cyclopropyl carbene complex 28 induced a vinylcyclopropyl rearrangement involving the photogenerated ketene moiety to provide α-alkoxy cyclopentenone 29.

Full text of DOI:10.1021/ja9537585

VOLUME 118, NUMBER 34
AUGUST 28, 1996
© Copyright 1996 by the
American Chemical Society
Photoreactions of γ,δ-Unsaturated Chromium Carbene
Complexes
William H. Moser and Louis S. Hegedus*
Contribution from the Department of Chemistry, Colorado State UniVersity,
Fort Collins, Colorado 80523
ReceiVed NoVember 8, 1995X
Abstract: A number of functionalized γ,δ-unsaturated chromium carbene complexes were synthesized, and their
photochemistry was studied. Photolysis of carbene complexes 5 and 17 induced intramolecular [2 + 2] cycloaddition
to afford cyclobutanones 6 and 18, respectively. If the photoreactions were not run in thoroughly degassed solvents,
small amounts of lactones 7 and 19 were obtained as well. Cyclobutanones 6 and 18 were stable once isolated, but
underwent an acid-catalyzed Pinacol rearrangement/hydrolysis transformation in acidic solution to afford novel
R-hydroxy-substituted bicyclo[3.1.0]hexanone compounds 20 and 21. Photolysis of cyclopropyl carbene complex
28 induced a vinylcyclopropyl rearrangement involving the photogenerated ketene moiety to provide R-alkoxy
cyclopentenone 29.
Introduction
The use of chromium carbene complexes as substrates in
pericyclic reactions has become accepted as an important method
for the synthesis of natural products. One of the most notable
developments has been the use of chromium carbene complexes
in benzannulation reactions, allowing for convergent syntheses
of complex aromatic systems.1 Thermally driven benzannula-
tion reactions based on alkyne cycloadditions to chromium
carbene complexes were first reported in 19752 and have found
many applications since then in the synthesis of p-alkoxyphenols
and 1,4-quinones (eq 1).3 More recently, photochemically
driven benzannulation reactions of chromium carbene complexes
have provided an efficient route to o-alkoxy- or amino-
substituted phenolic products (eq 2).4
The proposed reaction mechanisms of these benzannulation
reactions all involve as the key step the electrocyclic ring closure
of a dienyl ketene intermediate, leading to the formation of a
new aromatic ring. In contrast, pericyclic reactions of R,â-
saturated, γ,δ-unsaturated ketenes have remained relatively
unexplored.5 As shown in eq 3, it was envisioned that such an
intermediate, photochemically derived from chromium carbene
X Abstract published in AdVance ACS Abstracts, August 1, 1996.
S0002-7863(95)03758-9 CCC: $12.00 © 1996 American Chemical Society

7874 J. Am. Chem. Soc., Vol. 118, No. 34, 1996
Moser and Hegedus
complexes, would be an amenable substrate for sigmatropic
Cope rearrangement. A saturated ring system in the R,â-
position would result, not in a benzannulation process, but rather
in the opening of the cyclic moiety to form a larger ring system
as the product. The successful realization of this process would
thus provide a novel entry into a variety of medium-sized cyclic
compounds.
equatorial position, olefin-ketene [2 + 2] cycloaddition can
only occur from the energetically more favored exo rotamer of
the olefin (shown) leading to 6. The endo olefin rotamer would
not be able to achieve the requisite perpendicular transition state9
for cycloaddition and would suffer serious steric hindrance from
the axial hydrogen at the 3-position. The product was identified
Results and Discussion
Initial experiments made use of cis-vinylcyclohexyl chromium
carbene complex 5, which was prepared as shown in Scheme
1. Commercially available cis-1,2-cyclohexanedicarboxylic
by a characteristic cyclobutanone IR absorbance at 1787 cm-1
,
Scheme 1
as well as a 13C NMR signal for the carbonyl carbon at δ 200.
1
In addition, the H NMR signals for the bridging methylene
group and adjacent methine of 6 correlated well with those
reported for the parent bicyclo[2.1.1]hexan-5-one.10
Although similar intramolecular cycloadditions with longer
tethers are well-known,11 formation of 6 was unexpected, as
the use of two-atom tethers in attempted syntheses of oxabi-
cyclohexanones has been reported to fail.12 Furthermore, the
regiochemistry of the observed cycloaddition results from bond
formation between the internal olefin carbon and the central
carbon of the ketene; this is the opposite of what is expected
by electronic considerations.9 This reversal of regioselectivity
is most likely due to the strain inherent in a [2.2.0] bicyclo-
hexanone cis-fused to a cyclohexane ring. Attempts to favor
Cope rearrangement over intramolecular cycloaddition by use
of Pd(II) salts or Lewis acids as catalysts13 resulted only in
reduced yields of 6 and significant carbene complex decomposi-
tion. Conversely, attempts to disfavor cycloaddition by use of
electron rich aminocarbene complexes gave no reaction at all.
Although photolysis of 5 in thoroughly degassed THF, CH2-
Cl2, or benzene solvents resulted in the formation of 6 as the
sole product, the use of solvents which were not degassed
produced inseperable mixtures (approximately 6:1 ratio) of 6
and a new lactone 7, with 6 always predominating (eq 5).
anhydride (1) was reduced to hydroxy lactone 2 by LiAlH(Ot-
Bu)3.6 Subsequent ring opening and Wittig olefination with
methylenetriphenylphosphorane afforded cis-carboxylic acid 3,
which underwent reaction with oxalyl chloride to cleanly provide
cis-acid chloride 4. Published chromium dianion chemistry7,8
was then employed to afford the desired cis-carbene complex
5. Maintenance of the cis disposition of the groups on the
cyclohexane ring was verified by 1H NMR. The signal for the
methine proton R to the carbene carbon (δ 4.19) has coupling
constants of 3.8, 3.8, and 10.3 Hz, consistent with one axial-
axial coupling and two axial-equatorial couplings which are
necessitated by the cis stereochemistry, assuming the large
chromium moiety is in an equatorial position. Photolysis of
carbene complex 5 in THF solvent under 45 psi of CO did not
result in a Cope rearrangement, but rather in an intramolecular
[2 + 2] cycloaddition between the ketene and olefin moieties
to afford cyclobutanone 6 as a single diastereoisomer in 78%
yield (eq 4). With the large metal-bound ketene group in the
The structure of 7 was initially elusive since it is not merely
a constitutional isomer of 6 but contains an additional carbon
and oxygen atom, as evidenced by high-resolution exact mass
spectral analysis. The 13C chemical shift of δ 177 for the
(1) For reviews see: (a) Do¨tz, K. H. Angew. Chem. Int. Ed. Engl. 1984,
23, 587. (b) Wulff, W. D. Metal Carbene Cycloadditions. In ComprehensiVe
Organic Synthesis; Trost, B. M., Ed.; Pergamon: London, 1991; Vol. 5,
pp 1065-1113.
(2) Do¨tz, K. H. Angew. Chem., Int. Ed. Engl. 1975, 14, 644.
(3) Do¨tz, K. H. New J. Chem. 1990, 14, 433. For a recent, comprehensive
review see: Wulff, W. D. In ComprehensiVe Organometallic Chemistry
II; Abel, E. W., Stone, F. G. A., Wilkinson, G., Eds.; Pergamon: Oxford,
UK, 1995; Vol. 12, pp 469-547.
(4) (a) Merlic, C. A.; Xu, D. J. Am. Chem Soc. 1991, 113, 7418. (b)
Merlic, C. A.; Xu, D. J. Org. Chem. 1993, 58, 538.
(5) (a) Freeman, P. K.; Kuper, D. G. Chem. Ind. 1965, 424. (b) Meinwald,
J.; Wahl, G. H., Jr. Chem. Ind. 1965, 425.
(9) Valent´ı, E.; Perica`s, M. A.; Moyano, A. J. Org. Chem. 1990, 55,
3582.
(10) Wiberg, K. B.; Lowry, B. R.; Nist, B. J. J. Am. Chem. Soc. 1962,
84, 1594.
(11) For reviews see: (a) Snider, B. B. Chem. ReV. 1988, 88, 793. (b)
Ernst, B.; DeMesmaeker, A.; Hans, G.; Veenstra, S. J. NATO ASI Ser.,
Ser. C 1989, 273, 207. (c) Hyatt, J. A.; Raynolds, P. W. Org. React. 1994,
45, 159.
(6) Cannone, P.; Akssira, M. Tetrahedron 1985, 41, 3695.
(7) Semmelhack, M. F.; Lee, G. R. Organometallics 1987, 6, 1839.
(8) Schwindt, M. A.; Lejon, T.; Hegedus, L. S. Organometallics 1990,
9, 2814.
(12) (a) Snider, B. B.; Hui, R. A. H. F. J. Org. Chem. 1985, 50, 5167.
(b) Soderberg, B. C.; Hegedus, L. S.; Sierra, M. A. J. Am. Chem. Soc.
1990, 112, 4364.
(13) Lutz, R. P. Chem. ReV. 1984, 84, 205.

Photoreactions of Chromium Carbene Complexes
J. Am. Chem. Soc., Vol. 118, No. 34, 1996 7875
carbonyl carbon, together with an IR absorbance of 1792 cm-1
,
Scheme 2
suggested the 5-membered lactone ring as shown; the 13C
spectrum also has two quaternary carbon signals at δ 137 and
1
125, indicative of the olefin moiety. The H NMR spectrum
contains signals for the methylene protons adjacent to the lactone
(δ 2.64 and 2.21) which have geminal coupling constants of
17.1 and vicinal coupling constants with the adjacent methine
of 11.0 and 8.4, again consistent with the rigid tricyclic ring
structure of 7. The stereochemistry of 7 follows directly from
that of 6 (see Scheme 2). MM2 calculations14 indicated that
the isomer shown, with the lactone bridgehead hydrogen
“down”, was ≈8 kcal/mol more stable than the isomer with
this hydrogen “up”, and the calculated coupling constants for 7
(10.9, 7.2 Hz) more closely approximate those observed (11.0,
8.4 Hz) than do those calculated for the other isomer (12.0, 5.5
Hz).
Further evidence is provided by base hydrolysis of 7, followed
by treatment with diazomethane to produce methyl ester 8 (eq
6). DQF-COSY NMR techniques established the assignments
shown in eq 6, and HMBC techniques established that the ester
carbonyl carbon was strongly coupled to both protons of the
σ-CH2 group (δ 2.73, 2.56) while that of the ketone coupled to
the methine at δ 2.38 and much less strongly (3 bond coupling)
to only the upfield proton of the σ-CH2 group.15 This, along
with a ketone carbonyl infrared absorption at 1738 cm-1 (rather
than 1715 cm-1 expected for a cyclohexanone) is more con-
sistent with the structure shown in eq 8 than a regioisomer
having a fused cyclohexanone with a â-CO2Me group.15 The
coupling constant of 7.4 Hz between the ring-fused methine
and the proton geminal to the methoxy substituent is only
consistent with the methoxy group being anti to the bridgehead
methine, since MM214 calculations predict a value of 7.2 Hz
for this isomer and 0.8 Hz for the syn isomer. The relative
stereochemistry of the CH2CO2Me group could not be un-
equivocally assigned. That shown is for the isomer calculated
to be the more stable (≈3 kcal/mol) of the two possible isomers
having the OMe group “down”.
Scheme 3
The formation of lactone 7 is mechanistically interesting and
a possible pathway involving the same intermediate responsible
for the production of 6 is presented in Scheme 2. Chromium-
mediated ketene-olefin cycloaddition could proceed through
bicyclic intermediate 9, produced as shown in the scheme.16
Reductive elimination would directly form the major observed
product 6. Intermediate 9 is a chromium C-enolate. Rear-
rangement to the O-enolate 10, followed by insertion of CO
into the chromium carbon bond,17 would give 11. Reductive
elimination would then produce the minor product 7. Alter-
natively,15 traces of oxidized chromium residues might act as a
Lewis acid, catalyzing the Pinacol rearrangement/cyclopropyl-
carbynyl ring opening process shown in the lower half of the
scheme.
Further experiments made use of trans-carbene complex 16
which was prepared as shown in Scheme 3. The trans
disposition of the groups on the cyclohexane ring was obtained
by treatment of hydroxy lactone 2 with 1 N KOH which effected
ring opening and epimerization to produce compound 13. The
(14) Calculations were carried out on a Silicon Graphics Iris computer
using Micromodel Version 4.0. Allinger, N. L. J. Am. Chem. Soc. 1977,
99, 8124. Liljefor, T.; Tai, J. C.; Li, S.; Allinger, N. L. J. Comp. Chem.
1987, 8, 1051. Sprague, J. T.; Tai, J. C.; Yuh, Y.; Allinger, N. L. J. Comp.
Chem. 1987, 8, 581.
(15) NMR measurments were carried out and interpreted by Dr. Chris
Rithner of this department. We thank an astute referee for suggesting
structure 8 as a more reasonable structure than the 2-decalinone regioisomer
originally proposed by the authors, and for suggesting an alternate
mechanism for its formation.
(16) Chromium-mediated [2 + 2] cycloaddition in both ketene-olefin
and ketene-imine reactions has been previously proposed to rationalize
differences in stereochemistry between these reactions involving free ketenes
and those involving photogenerated chromium-ketene complexes. Hegedus,
L. S.; Montgomery, J.; Narukawa, Y.; Snustad, D. C. J. Am. Chem. Soc.
1991, 113, 5784.
(17) Slack, D. A.; Egglestone, D. L.; Baird, M. C. J. Organomet. Chem.
1978, 146, 71.

7876 J. Am. Chem. Soc., Vol. 118, No. 34, 1996
Moser and Hegedus
Scheme 4
Scheme 5
remainder of the steps were then carried out as previously
1
described to afford 16. The H NMR signal for the methine
proton R to the carbene carbon in 16 (δ 3.83) has coupling
constants of 2.9, 11.0, and 11.0 Hz, consistent with 2 axial-
axial couplings and 1 axial-equatorial coupling as expected
for the trans diequatorial disposition of the two groups on the
cyclohexane ring. Photolysis of 16 under the same conditions
as used for the cis-carbene complex did not result in the desired
Cope rearrangement, and in fact afforded a complex mixture
of products, with intramolecular cycloaddition products only
seen in trace amounts, and a lactone analogous to 7 not observed
at all.
Photolytic reactions of the acyclic γ,δ-unsaturated chromium
carbene complex 17 were also studied. To prepare 17, the
(benzyloxy)(methyl)chromium carbene complex18 was depro-
tonated with n-BuLi at -78 °C, followed by alkylation with
allyl bromide at 0 °C (eq 7).19 The results of photolysis
consistent with those for related [3.1.0] systems (1710-1730
cm-1),21 compared with the normal 1750 cm-1 for simple
cyclopentanones. A similar rearrangement took place with 6
to provide the tricyclic R-hydroxy ketone 21 (eq 9). Such
contractions of four-membered rings to three-membered rings
are rare, and have been of interest in the synthesis of compounds
containing functionalized cyclopropyl rings.22
At this point, attention was turned to vinylcyclopropyl carbene
complexes. It was anticipated that photogenerated vinylcyclo-
propyl ketene complexes would undergo more facile Cope
rearrangement than would vinylcyclohexyl ketene complexes,
since cis-1,2-divinylcyclopropanes undergo Cope rearrange-
ments much more readily than cis- or trans-divinylcyclohexanes
due to the strain present in the cyclopropyl ring.23 Accordingly,
cis-vinylcyclopropyl carbene complex 28 was prepared as shown
in Scheme 5.
experiments with 17 mirrored those of the cis-carbene complex
5. The use of carefully degassed solvents in the photolyses
provided cyclobutanone 18 as the sole product, whereas
photolyses using non-degassed solvents afforded inseparable
mixtures of 18 as the major product and lactone 19 in minor
amounts (approximately 6:1 ratio) (eq 8).
Ethyl chrysanthemate (22), commercially available as a
mixture of cis and trans isomers, was ozonized to produce
aldehyde 23. When heated at reflux in a NaOMe/MeOH
solution, 23 becomes trapped as the cis-methoxy lactone 24.24
Heating 24 at reflux in dioxane/H2O provides hydroxy lactone
25; ring opening and Wittig olefination with methylenetriphen-
ylphosphorane then affords carboxylic acid 26.24 Transforma-
tion to acid chloride 27 with oxalyl chloride followed by
chromium dianion chemistry7,8 provides carbene complex 28.
Photolysis of 28 in CH2Cl2 under 60 psi of CO, however,
afforded an 83% yield of R-alkoxycyclopentenone 29, the
product of a formal vinylcyclopropane rearrangement involving
the ketene moiety (eq 10).
The bicyclo[2.1.1]hexanone 18, while containing a strained
ring system, is stable once isolated. However, in the presence
of acidic aqueous media, 18 undergoes a facile acid-catalyzed
Pinacol rearrangement and hydrolysis process to afford the
R-hydroxy bicyclo[3.1.0]hexanone 20 in essentially quantitative
yield (Scheme 4). This bicyclo[3.1.0]hexane system showed
13C-H coupling constants characteristic for this system (t, JCH
) 164 Hz, cyclopropyl CH2; d, J ) 173 Hz, cyclopropyl CH;
t, J ) 131 Hz, cyclopentyl CH2; t, J ) 132 Hz, cyclopentyl
CH2 vs 161, 166, 130, and 130 Hz for the corresponding carbons
in the parent bicyclo[3.1.0]hexane itself).20 Similarly, the
observed infrared CO stretching frequency of 1722 cm-1 is quite
Although vinylcyclopropane rearrangements are thermally
forbidden [π2s + σ2s] transformations and generally require
temperatures of 200-300 °C to proceed,25 the presence of the
(18) Hafner, A.; Hegedus, L. S.; deWeck, G.; Hawkins, B.; Do¨tz, K. H.
J. Am. Chem. Soc. 1988, 110, 8413.
(19) This procedure results in some dialkylation: Casey, C. P.; Brunsvold,
W. R. J. Organomet. Chem. 1976, 118, 309. In our hands, typically <10%
of the dialkylated product was observed, which was not problematic when
carried on to subsequent steps.
(21) See, for examples: Ziegler, F. E.; Petersen, A. K. J. Org. Chem.
1994, 59, 2707.
(22) See: Ihara, M.; Taniguchi, T.; Tokunaga, Y.; Fukumoto, K. J. Org.
Chem. 1994, 59, 8092 and references therein.
(23) Brown, J. M.; Golding, B. T.; Stofko, J. J., Jr. J. Chem. Soc., Chem.
Commun. 1973, 319.
(20) Kalinowski, H.-O.; Berger, S.; Braun, S. Carbon-13 NMR Spec-
troscopy; John Wiley and Sons, Ltd.: New York, 1988; p 497.
(24) Dauben, W. G.; Dinges, J.; Smith, T. C. J. Org. Chem. 1993, 58 ,
7635.

Photoreactions of Chromium Carbene Complexes
J. Am. Chem. Soc., Vol. 118, No. 34, 1996 7877
carboxylic anhydride (1) (3.85 g, 25.0 mmol) was taken up in THF
(15 mL) and cooled to -20 °C in an ethylene glycol/CO2 bath. This
was added to a -20 °C solution of LiAlH(Ot-Bu)3 (7.95 g, 31.3 mmol)
in THF (25 mL) via a cannula, and the resultant solution was allowed
to slowly warm to room temperature with stirring over 7 h. Aqueous
10% HCl solution was then added until all solids were dissolved. The
solution was extracted with CH2Cl2 (4 × 15 mL) and the combined
organic layers were washed with brine (1 × 15 mL) and dried over
MgSO4. Filtration and removal of solvents under reduced pressure gave
the crude product as a yellow oil. Purification via flash chromatography
(SiO2, 1/1 hexanes/EtOAc) afforded 2 (2.52 g, 65% yield) as a clear,
carbonyl π orbitals of the ketene provides a thermally allowed
pericyclic [(π2s + π2s) + σ2s] reaction pathway for the
cyclopropyl ketene intermediate.26 To test the generality of this
reaction, (benzyloxy)(cyclopropyl) carbene complex 30a was
photolyzed, and did in fact afford cyclopentenone 31a as the
sole product in 68% yield (eq 11). The electron rich (dimeth-
1
colorless oil. The H spectrum was consistent with that reported in
the literature.6 1H NMR δ 5.5 (br s, 1H), 4.3 (br s, 1H), 2.96 (m, 1H),
2.42-2.36 (m, 1H), 2.11-2.07 (m, 1H), 1.86-1.82 (m, 1H), 1.63-
1.53 (m, 3H), 1.23-1.10 (m, 3H).
cis-Carboxylic Acid 3. Methyltriphenylphosphonium bromide (3.14
g, 8.80 mmol) was taken up in THF (15 mL) under argon atmosphere
and cooled to 0 °C. n-BuLi (5.9 mL of a 1.5 M solution in hexanes,
8.8 mmol) was added dropwise via syringe. The resultant red solution
was allowed to stir at 0 °C for 30 min, and a solution of hydroxy lactone
2 (624 mg, 4.00 mmol) in THF (10 mL) was added dropwise via
syringe. The solution was allowed to slowly warm to room temperature
with stirring over 4 h. Aqueous 10% NaOH solution was then added
until all solids had dissolved, and the solution was extracted with EtOAc
(3 × 15 mL). The combined aqueous layers were treated with 3 N
HCl to pH 3 and extracted with EtOAc (3 × 15 mL). The combined
organic layers were washed with brine (1 × 10 mL) and dried over
MgSO4. Filtration and removal of solvents under reduced pressure gave
the crude product as a yellow oil. Purification via flash chromatography
(SiO2, 4/1 hexanes/EtOAc) afforded 3 (372 mg, 60% yield) as a clear,
colorless oil. 1H NMR δ 11.6 (br s, 1H), 5.96 (ddd, J1 ) 7.9 Hz, J2 )
10.4 Hz, J3 ) 17.2 Hz, 1H), 5.06 (dd, J1 ) 1.0 Hz, J2 ) 16.8 Hz, 1H),
5.02 (dd, J1 ) 1.0 Hz, J2 ) 10.3 Hz, 1H), 2.67 (m, 1H), 2.59 (ddd, J1
) J2 ) 4.3 Hz, J3 ) 8.7 Hz, 1H), 1.82-1.67 (m, 4H), 1.59-1.52 (m,
2H), 1.43-1.32 (m, 2H); 13C NMR δ 181.1, 138.2, 115.7, 45.9, 41.1,
30.1, 24.5, 24.2, 22.0; IR (neat) ν 3100-2600, 1704 cm-1. Anal. Calcd
for C9H14O2: C, 70.10; H, 9.15. Found: C, 69.93; H, 8.96.
ylamino)(cyclopropyl) carbene complex 30b27 was likewise
examined, but in this case no reaction occurred. Similar
transformations of chromium carbene complexes have been
explored by Herndon, in which thermally induced Cope rear-
rangements involving the carbene complex dπ-pπ bond are
proposed as the key step in the preparation of R-alkoxy
cyclopentenones.28
In summary, photochemically driven Cope rearrangements
of chromium carbene complexes were not observed due to the
presence of more favorable pericyclic reaction pathways avail-
able to the intermediate ketene species. Photolysis of acyclic
and cyclohexyl γ,δ-unsaturated alkoxycarbene complexes re-
sulted in intramolecular [2 + 2] cycloadditions to afford bicyclo-
[2.1.1]hexanones. Photolytic reactions performed in non-
degassed solvents also afforded lactones in minor amounts as
well. The bicyclohexanone compounds underwent a Pinacol
rearrangement/hydrolysis transformation to afford R-hydroxy
ketones. Vinylcyclopropyl carbene complexes underwent pho-
tochemically driven ketenylcyclopropyl rearrangements to pro-
duce R-alkoxy cyclopentenones.
cis-Acid Chloride 4. cis-Carboxylic acid 3 (885 mg, 5.74 mmol)
was taken up in CH2Cl2 (10 mL), and oxalyl chloride (0.60 mL, 6.88
mmol) was added via syringe. The resultant solution was allowed to
stir at room temperature for 45 min and solvents were removed under
reduced pressure to give the crude product as a slightly brown oil.
Purification via Kugelrohr distillation afforded 4 (897 mg, 95% yield)
as a clear, colorless oil. 1H NMR δ 5.91 (ddd, J1 ) 8.1 Hz, J2 ) 10.3
Hz, J3 ) 17.2 Hz, 1H), 5.15 (dd, J1 ) 1.4 Hz, J2 ) 17.2 Hz, 1H), 5.09
(dd, J1 ) 1.4 Hz, J2 ) 10.4 Hz, 1H), 3.01 (ddd, J1 ) J2 ) 4.3 Hz, J3
) 8.9 Hz, 1H), 2.83 (m, 1H), 1.91-1.78 (m, 3H), 1.67-1.54 (m, 3H),
1.46-1.38 (m, 2H); 13C NMR δ 175.1, 136.7, 116.9, 58.4, 41.5, 30.0,
Experimental Section
1
General Procedures. The 300-MHz H NMR and 75.5 MHz 13C
NMR spectra were obtained on a Bruker ACE-300 spectrometer.
1
Chemical shifts are given in ppm relative to (CH3)4Si (0 ppm, H) or
25.6, 23.8, 21.9; IR (neat) ν 1795 cm-1
.
CDCl3 (77.0 ppm, 13C) unless otherwise noted. Elemental analyses
were performed by M-H-W Laboratories, Phoenix, AZ. All reactions
were performed under an atmosphere of argon except as specified.
Photoreactions were carried out using a 450-W 7825 medium-pressure
Hg lamp immersed in a Pyrex well. The crude reaction mixtures were
purified by column chromatography with silica gel (ICN Biomedicals
Silitech 32-63 µm).
cis-Carbene Complex 5. This carbene complex was prepared via
a modification of Semmelhack and Lee’s method.7 An airless flask
8
containing K2Cr(CO)5 (2.72 mmol) in THF (15 mL) was cooled to
-78 °C. cis-Acid chloride 4 (468 mg, 2.72 mmol) in THF (5 mL)
was added via syringe under argon atmosphere, and the resultant green-
black mixture was stirred at -78 °C for 15 min, at 0 °C for 1.5 h, and
at room temperature for 1 h. The solvents were removed under reduced
pressure and the residue was taken up in chilled, degassed H2O (20
Materials. cis-Cyclohexanedicarboxylic anhydride, methyltriphen-
ylphosphonium bromide, oxalyl chloride, ethyl chrysanthemate, and
acetyl bromide were purchased from Aldrich and used as received.
Trimethyloxonium tetrafluoroborate was purchased from Strem and
used as received.
-
mL). Me3O+BF4 (400 mg, 2.72 mmol) was added in portions over
15 min. The solution was filtered through Celite and extracted with
hexanes (5 × 15 mL). The combined organic layers were dried over
MgSO4, filtered, and concentrated to an orange oil. Purification via
flash chromatography (SiO2, hexanes) afforded 5 (673 mg, 72% yield)
as an orange solid. 1H NMR δ 5.94 (ddd, J1 ) 10.0 Hz, J2 ) 10.2 Hz,
J3 ) 16.9 Hz, 1H), 4.92 (dd, J1 ) 1.8 Hz, J2 ) 10.2 Hz, 1H), 4.87 (dd,
J1 ) 1.8 Hz, J2 ) 17.0 Hz, 1H), 4.70 (s, 3H), 4.19 (ddd, J1 ) J2 ) 3.8
Hz, J3 ) 10.3 Hz, 1H), 2.81 (m, 1H), 1.73-1.44+1.4-1.2 (m, 8H);
13C NMR δ 366.2, 223.1, 216.5, 138.4, 114.8, 73.6, 67.2, 41.8, 32.5,
24.9, 23.6, 21.3; IR (neat) ν 2060, 1918 cm-1; MS 344 (M+).
Hydroxy Lactone 2. This compound was prepared using a slight
modification of the reported literature procedure.6 cis-Cyclohexanedi-
(25) Hudlicky, T.; Kutchan, T. M.; Naqui, S. M. Org. React. 1984, 33,
247.
(26) Based on arguments in: (a) Zimmerman, H. E. In Pericyclic
Reactions; Marchand, A. P., Lehr, R. E., Eds.; Academic Press: New York,
1977; Vol. I, p 77. (b) Ghosez, L.; O’Donnell, M. J. In Pericyclic Reactions;
Marchand, A. P., Lehr, R. E., Eds.; Academic Press: New York, 1977;
Vol. II, p 87.
(27) Hegedus, L. S.; Schwindt, M. A.; De Lombaert, S.; Imwinkelried,
R. J. Am. Chem. Soc. 1990, 112, 2264.
(28) Herndon, J. W.; McMullen, L. A. J. Am. Chem. Soc. 1989, 111,
6854.
Cyclobutanone 6. Carbene complex 5 (57 mg, 0.166 mmol) was
taken up in THF (15 mL) in an airless flask equipped with a sidearm.
The resultant yellow-orange solution was degassed (freeze-pump-
thaw degassing using liquid N2, 3 cycles) and transferred to an Ace

7878 J. Am. Chem. Soc., Vol. 118, No. 34, 1996
Moser and Hegedus
pressure tube. The pressure tube was charged to 45 psi of CO (3 cycles)
and irradiated at 25 °C for 16 h. The solvents were removed under
reduced pressure, and the residue was taken up in Et2O and decanted
away from Cr(CO)6. Purification of the organic layers via flash
chromatography (SiO2, 9/1 hexanes/EtOAc) afforded 6 (24 mg, 78%
(m, 2H), 2.0-1.9 (m, 1H), 1.8-1.7 (m, 3H), 1.5-1.1 (m, 4H); 13C
NMR δ 181.9, 141.0, 114.5, 49.1, 43.5, 31.5, 29.3, 25.2, 25.0; IR (neat)
ν 3200-2800, 1706 cm-1. Anal. Calcd for C9H14O2: C, 70.10; H,
9.15. Found: C, 70.20; H, 8.92.
trans-Acid Chloride 15. trans-Carboxylic acid 14 (760 mg, 4.93
mmol) was taken up in CH2Cl2 (15 mL), and oxalyl chloride (0.54
mL, 6.16 mmol) was added via syringe. The resultant solution was
allowed to stir at room temperature for 1 h and solvents were removed
under reduced pressure to give the crude product as a slightly brown
oil. Purification via Kugelrohr distillation afforded 15 (798 mg, 94%
yield) as a clear, colorless oil. 1H NMR δ 5.67 (ddd, J1 ) 7.8 Hz, J2
) 10.2 Hz, J3 ) 17.9 Hz, 1H), 5.08 (dd, J1 ) 1.1 Hz, J2 ) 17.2 Hz,
1H), 5.02 (dd, J1 ) 1.1 Hz, J2 ) 10.3 Hz, 1H), 2.60 (ddd, J1 ) 3.5 Hz,
J2 ) J3 ) 10.8 Hz, 1H), 2.33 (m, 1H), 2.17-2.11 (m, 1H), 1.84-1.73
(m, 3H), 1.57-1.51 (m, 2H), 1.34-1.12 (m, 3H); 13C NMR δ 176.1,
1
yield) as a clear, colorless oil. H NMR δ 3.47 (s, 3H), 2.47 (m, 1H),
2.09 (m, 2H), 1.87 (dd, J1 ) 3.6 Hz, J2 ) 6.9 Hz, 1H), 1.62 (d, J )
6.9 Hz, 1H), 1.65-1.49 + 1.31-1.16 (m, 8H); 13C NMR δ 199.7, 95.7,
54.6, 50.3, 35.7, 35.5, 27.9, 23.4, 20.6, 19.2, 18.8; IR (neat) ν 1787
cm-1. Anal. Calcd for C11H16O2: C, 73.30; H, 8.95. Found: C, 73.46;
H, 8.72.
Lactone 7. The preceding procedure was followed, except that non-
degassed CH2Cl2 (7 mL) was used as the solvent. Irradiation for 16 h
at 25 °C produced an oil which was purified by flash chromatography
(SiO2, 6/1 hexanes/EtOAc) to afford 25 mg of a 6/1 mixture of 6 and
7. Spectral data for 7: 1H NMR δ 3.80 (s, 3H), 3.19 (m, 1H), 2.64
(dd, J1 ) 8.4 Hz, J2 ) 17.1 Hz, 1H), 2.30 (m, 1H), 2.21 (dd, J1 ) 11.0
Hz, J2 ) 17.1 Hz, 1H), the remaining cyclohexyl protons were obscured
by the signals for compound 6. 13C NMR δ 177.4, 137.1, 125.1, 58.6,
139.7, 115.8, 60.4, 44.0, 31.3, 29.1, 24.9, 24.7; IR (neat) ν 1794 cm-1
.
Anal. Calcd for C9H13ClO: C, 62.61; H, 7.59. Found: C, 62.42; H,
7.39.
trans-Carbene Complex 16. This carbene complex was prepared
44.5, 43.8, 41.1, 35.9, 29.2, 26.7, 23.5, 22.0; IR (neat) ν 1792 cm-1
.
via a modification of Semmelhack and Lee’s method.7 An airless flask
8
HRMS calcd for C12H16O3 208.1099, found 208.1096.
containing K2Cr(CO)5 (2.06 mmol) in THF (15 mL) was cooled to
-78 °C. trans-Acid chloride 15 (355 mg, 2.06 mmol) in THF (5 mL)
was added via syringe under argon atmosphere, and the resultant green-
black mixture was stirred at -78 °C for 25 min, at 0 °C for 1.5 h, and
at room temperature for 1 h. The solvents were removed under reduced
pressure and the residue was taken up in chilled, degassed H2O (20
Compound 8. A mixture of 6 and 7 (90 mg) was taken up in Et2O
(10 mL), and an aqueous 10% NaOH solution (10 mL) was added.
The resultant biphasic solution was allowed to stir vigorously for 2 h.
The layers were separated, and the aqueous layer was acidified to pH
2 with 1 N HCl, then extracted with EtOAc (3 × 10 mL). The
combined EtOAc layers were dried over MgSO4, filtered, and concen-
trated to afford 24 mg of a slightly pink oil. This oil was taken up in
freshly distilled Et2O (15 mL), and an excess of diazomethane (>3
equiv, generated by the addition of aqueous 10% NaOH to a solution
of Diazald in EtOH) was bubbled through the solution until a yellow
color persisted. Argon was then bubbled through the solution for 10
min to remove excess diazomethane. The solution was concentrated
to a yellowish oil and purified by flash chromatography (SiO2, 2/1
-
mL). Me3O+BF4 (304 mg, 2.06 mmol) was added in portions over
15 min. The solution was filtered through Celite and extracted with
hexanes (5 × 15 mL). The combined organic layers were dried over
MgSO4, filtered, and concentrated to an orange oil. Purification via
flash chromatography (SiO2, hexanes) afforded 16 (411 mg, 58% yield)
as an orange oil. 1H NMR δ 5.65 (ddd, J1 ) 9.0 Hz, J2 ) 11.3 Hz, J3
) 16.9 Hz, 1H), 4.86 (dd, J1 ) 1.9 Hz, J2 ) 11.1 Hz, 1H), 4.84 (dd,
J1 ) 1.9 Hz, J2 ) 16.9 Hz, 1H), 4.77 (s, 3H), 3.83 (ddd, J1 ) 2.9 Hz,
J2 ) J3 ) 11.0 Hz, 1H), 2.25 (m, 1H), 1.92 (m, 1H), 1.81-1.63 (m,
4H), 1.28-1.22 (m, 4H), 0.98-0.83 (m, 1H); 13C NMR δ 368.9, 223.3,
216.4, 141.6, 113.9, 75.6, 67.6, 46.2, 32.0, 29.5, 25.6, 25.5; IR (neat)
ν 2061, 1922 cm-1; MS 344 (M+).
Carbene Complex 17. [(Benzyloxy)(methyl)carbene]pentacarbonyl
chromium(0)16 (800 mg, 2.45 mmol) was taken up in THF (20 mL)
under argon and cooled to -78 °C. n-BuLi (1.52 mL of a 1.6 M
solution in hexanes, 2.45 mmol) was added via syringe, and the resultant
solution was allowed to stir at -78 °C for 30 min. Allyl bromide
(0.23 mL, 2.70 mmol) was added in one portion via syringe. The
solution was allowed to warm to 0 °C and stirred for 2 h. The reaction
was quenched by addition of wet Et2O (5 mL) and concentrated to an
orange oil. Purification via flash chromatography (SiO2, hexanes)
afforded 17 (779mg, 87% yield) as an orange oil. 1H NMR δ 7.46 (br
s, 5H), 6.01 (s, 2H), 5.71 (dddd, J1 ) J2 ) 6.5 Hz, J3 ) 10.2 Hz, J4 )
16.8 Hz, 1H), 4.97 (d, J ) 17.2 Hz, 1H), 4.96 (d, J ) 10.2 Hz, 1H),
3.46 (t, J ) 7.5 Hz, 2H), 2.21 (q, J ) 7.3 Hz, 2H); 13C NMR δ 360.0,
223.0, 216.3, 136.2, 133.9, 129.3, 128.9, 128.5, 115.8, 83.7, 62.0, 30.4;
IR (neat) ν 2061, 1951 cm-1; MS 366 (M+).
Bicyclo[2.1.1]hexanone 18. Carbene complex 17 (98 mg, 0.268
mmol) was taken up in freshly distilled THF (10 mL) in a flame-dried
airless flask equipped with a sidearm. The orange solution was
degassed (freeze-pump-thaw degassing using liquid N2, 3 cycles) and
transferred to a flame-dried Ace pressure tube. The pressure tube was
charged to 80 psi of CO and irradiated for 21 h at 25 °C. The solution
was concentrated to an oil and purified via flash chromatography (SiO2,
3/1 hexanes/EtOAc) to afford 18 (30 mg, 57% yield) as a clear, colorless
oil. 1H NMR δ 7.38-7.27 (m, 5H), 4.86 (d, J ) 11.4 Hz, 1H), 4.67 (d,
J ) 11.4 Hz, 1H), 2.56 (m, 1H), 1.92-1.84 (m, 5H), 1.80 (m, 1H),
1.58 (d, J ) 7.2 Hz, 1H); 13C NMR δ 200.1, 137.6, 128.3, 127.7, 127.5,
91.8, 69.3, 44.9, 30.1, 23.5, 21.6; IR (neat) 1791 cm-1. Anal. Calcd
for C13H14O2: C, 77.20; H, 6.98. Found: C, 77.43; H, 6.89.
Lactone 19. The preceding procedure was followed, except that
non-degassed CH2Cl2 (7 mL) was used as the solvent. Irradiation for
18 h at 25 °C produced an oil which was purified via flash
chromatography (SiO2, 5/1 hexanes/EtOAc) to afford 30 mg of a 6/1
mixture of 18 and 19. Spectral data for 19: 1H NMR δ 7.36-7.29
(m, 5H), 5.14 (d, J ) 11.7 Hz, 1H), 5.08 (d, J ) 11.7 Hz, 1H), 3.29
1
hexane/EtOAc) to afford 9 mg of 8 as a clear, colorless oil. H NMR
δ 4.01 (d, J ) 7.2 Hz, 1H), 3.63 (s, 3H), 3.48 (s, 3H), 2.73 (dd, J1 )
5.8 Hz, J2 ) 17.1 Hz, 1H), 2.56 (dd, J1 ) 3.9 Hz, J2 ) 17.1 Hz, 1H),
2.50-2.35 (m, 2H), 2.15-2.05 (m, 1H), 1.76-1.52 (m, 5H), 1.34-
1.11 (m, 2H), 0.97-0.79 (m, 1H); 13C NMR δ 215.9, 172.1, 87.4, 58.4,
51.8, 41.6, 37.3, 33.9, 32.9, 24.9, 24.3, 21.9, 20.2; IR (neat) ν 1738;
HRMS calcd for C13H20O4 240.1362, found 240.1362.
trans-Carboxylic Acid/Aldehyde 13. Hydroxy lactone 2 (2.80 g,
17.9 mmol) was taken up in Et2O (30 mL) and extracted with aqueous
1 N KOH solution (3 × 15 mL). The combined aqueous layers were
treated with aqueous 10% HCl solution to pH 3 and extracted with
CH2Cl2 (3 × 15 mL). These combined organic layers were washed
with brine (1 × 15 mL) and dried over MgSO4. Filtration and removal
of solvents under reduced pressure gave the crude product as a yellowish
solid. Purification via recrystallization from EtOAc afforded 13 (2.77
1
g, 99% yield) as a white crystalline solid, mp 217-220 °C. H NMR
δ 12.0 (br s, 1H), 9.61 (s, 1H), 2.58 (m, 2H), 2.06 (m, 2H), 1.79 (m,
2H), 1.5-1.1 (m, 4H); 13C NMR δ 202.6, 181.1, 50.8, 42.4, 28.5, 25.1,
25.0, 24.8; IR (neat) ν 3400-2700, 1705. Anal. Calcd for C8H12O3:
C, 61.52; H, 7.74. Found: C, 61.76; H, 7.76.
trans-Carboxylic Acid 14. Methyltriphenylphosphonium bromide
(5.69 g, 14.1 mmol) was taken up in THF (15 mL) under argon
atmosphere and cooled to 0 °C. n-BuLi (9.4 mL of a 1.5 M solution
in hexanes, 14.1 mmol) was added dropwise via syringe. The resultant
red solution was allowed to stir at 0 °C for 30 min, and a solution of
compound 13 (1.00 g, 6.40 mmol) in THF (10 mL) was added dropwise
via syringe. The solution was allowed to slowly warm to room
temperature with stirring over 6 h. Aqueous 10% NaOH solution was
then added until all solids had dissolved, and the solution was extracted
with EtOAc (3 × 15 mL). The combined aqueous layers were treated
with 3 N HCl to pH 3 and extracted with EtOAc (3 × 15 mL). The
combined organic layers were washed with brine (1 × 10 mL) and
dried over MgSO4. Filtration and removal of solvents under reduced
pressure gave the crude product as a yellow oil. Purification via flash
chromatography (SiO2, 4/1 hexanes/EtOAc) afforded 14 (632 mg, 64%
yield) as a clear, colorless oil. 1H NMR δ 11.0 (br s, 1H), 5.68 (ddd,
J1 ) 7.4 Hz, J2 ) 10.3 Hz, J3 ) 17.4 Hz, 1H), 5.02 dd, J1 ) 1.7 Hz,
J2 ) 17.3 Hz, 1H), 4.94 (dd, J1 ) 1.7 Hz, J2 ) 10.4 Hz, 1H), 2.3-2.1

Photoreactions of Chromium Carbene Complexes
J. Am. Chem. Soc., Vol. 118, No. 34, 1996 7879
(m, 1H), 2.69 (m, 1H), 2.67 (dd, J1 ) 8.2 Hz, J2 ) 16.9 Hz, 1H), 2.34
(ddd, J1 ) 1.7 Hz, J2 ) 9.2 Hz, J3 ) 15.0 Hz, 1H), 2.26 (dd, J1 ) 11.4
Hz, J2 ) 16.9 Hz, 1H), 2.14 (ddd, J1 ) J2 ) 6.2 Hz, J3 ) 12.4 Hz,
1H), 1.65 (m, 1H); 13C NMR δ 177.1, 136.9, 130.1, 128.0, 127.8, 127.4,
was taken up in H2O (5 mL) and dioxane (10 mL) and heated to reflux
for 2.5 h. The solvents were removed under reduced pressure, and the
residue was taken up in EtOAc and dried over MgSO4. Filtration and
removal of solvents under reduced pressure afforded the crude product
as a yellow oil. Purification via flash chromatography (SiO2, 2/1
hexanes/EtOAc) afforded 25 (525 mg, 93% yield) as a white crystalline
solid, mp 86-89 °C (lit.29 mp 83.5-87 °C). The 1H spectrum was
consistent with that reported in the literature.24 1H NMR δ 5.43 (s,
1H), 2.05 (s, 2H), 1.13 (s, 3H), 1.12 (s, 3H).
126.1, 72.6, 40.9, 37.3, 32.6, 28.5; IR (neat) ν 1792 cm-1
.
Bicyclic Ketone 20. Bicyclohexanone 18 (101 mg, 0.500 mmol)
was taken up in wet Et2O and added to a 10% aqueous HCl solution.
The resultant biphasic solution was allowed to stir vigorously overnight.
The solution was then extracted with Et2O (3 × 10 mL) and the
combined organic layers were dried over MgSO4. Filtration and
removal of solvents under reduced pressure gave the crude product as
a clear, slightly yellow oil. Purification via flash chromatography (SiO2,
3/1 hexanes/EtOAc) afforded 20 (54 mg, 96% yield) as a clear, colorless
Carboxylic Acid 26. This compound was prepared via a modifica-
tion of the literature procedure.24 Methyltriphenylphosphonium bromide
(2.90 g, 8.12 mmol) was taken up in dry THF (15 mL) and cooled to
0 °C. n-BuLi (5.42 mL of a 1.5 M solution in hexanes, 8.12 mmol)
was added via syringe, and the resultant red solution was allowed to
stir 30 min at 0 °C. A solution of hydroxy lactone 25 (525 mg, 3.69
mmol) was added dropwise via syringe, and the solution was allowed
to slowly warm to room temperature with stirring over 13 h. The
reaction was quenched by addition of 10% aqueous NaOH until all
the solids had dissolved. The solution was extracted with EtOAc (3
× 15 mL). The combined organic layers were washed with additional
10% aqueous NaOH. The combined aqueous layers were treated with
3 N HCl to pH 3 and extracted with EtOAc (3 × 15 mL). These
organic layers were washed with brine (2 × 10 mL) and dried over
MgSO4. Filtration and removal of solvent under reduced pressure
afforded the crude product as a yellow oil. Purification via flash
chromatography (SiO2, 3/1 hexanes/EtOAc) afforded 26 (413 mg, 80%
yield) as a white crystalline solid, mp 49-52 °C (lit.30 mp 47-51 °C).
1
oil. H NMR δ 4.24 (br s, 1H), 2.24-2.16 (m, 1H), 2.14-2.05 (m,
3H), 1.81-1.76 (m, 1H), 1.51 (dd, J1 ) 8.4 Hz, J2 ) 5.4 Hz, 1H),
1.18 (dd, J1 ) J2 ) 5.4 Hz, 1H); 13C NMR δ 214.1, 66.8, 30.4, 28.6,
21.1, 21.0; IR (neat) ν 3399, 1722 cm-1. Anal. Calcd for C6H8O2:
C, 64.27; H, 7.19. Found: C, 64.20; H, 7.00.
Tricyclic Ketone 21. Cyclobutanone 6 (26 mg, 0.144 mmol) was
taken up in Et2O (10 mL) and added to a 10% aqueous HCl solution
(10 mL). The resultant biphasic solution was allowed to stir vigorously
overnight. The solution was then extracted with Et2O (3 × 10 mL),
and the combined organic layers were dried over MgSO4. Filtration
and removal of solvents under reduced pressure gave the crude product
as a clear, slightly yellow oil. Purification via flash chromatography
(SiO2, 2/1 Et2O/hexanes) afforded 21 (23 mg, 96% yield) as a clear,
colorless oil. 1H NMR δ 3.59 (s, 1H), 2.30-2.26 (m, 1H), 2.18-2.07
(m, 2H), 2.01-1.92 (m, 2H), 1.56-1.47 (m, 3H), 1.45-1.41 (m, 1H),
1.34-1.23 (m, 1H), 1.08-0.97 (m, 3H); 13C NMR δ 213.4, 65.8, 38.8,
1
The H spectrum was consistent with that reported in the literature.23
1H NMR δ 11.9 (br s, 1H), 6.06 (ddd, J1 ) J2 ) 10.0 Hz, J3 ) 17.1
Hz, 1H), 5.19 (dd, J1 ) 2.1 Hz, J2 ) 17.1 Hz, 1H), 5.06 (dd, J1 ) 2.1
Hz, J2 ) 10.4 Hz, 1H), 1.88 (dd, J1 ) J2 ) 9.1 Hz, 1H), 1.68 (d, J )
8.6 Hz, 1H), 1.27 (s, 3H), 1.18 (s, 3H).
35.0, 34.4, 32.1, 23.8, 22.7, 22.1, 21.4; IR (neat) ν 3383, 1717 cm-1
.
Anal. Calcd for C10H14O2: C, 72.26; H, 8.49. Found: C, 72.17; H,
8.33.
Compound 23. This compound was prepared via a modification
of the literature procedure.24 Ethyl chrysanthemate (22) (2.00 g, 10.2
mmol) was taken up in freshly distilled CH2Cl2 (15 mL). The solution
was cooled to -78 °C and ozonized oxygen was bubbled through until
a blue color persisted (ca. 25 min). Argon was bubbled through until
the solution became colorless (ca. 15 min). The solution was then added
to a 0 °C stirring solution of thiourea29 (388 mg, 5.10 mmol) in MeOH.
After the solution was stirred for 3 h, the thiourea S-dioxide precipitate
was filtered off and the solvents were removed under reduced pressure.
The residue was taken up in Et2O and washed with 5% aqueous
NaHCO3 (2 × 15 mL) and H2O (2 × 15 mL). The organic layers
were dried over MgSO4, filtered, and concentrated to a yellow oil.
Purification via Kugelrohr distillation afforded 23 (1.58 g, 91% yield)
Acid Chloride 27. Carboxylic acid 26 (91 mg, 0.649 mmol) was
taken up in CH2Cl2 (5 mL) and oxalyl chloride (85 µL, 0.973 mmol)
was added via syringe. The solution was allowed to stir for 1 h, after
which time the solvents were removed under reduced pressure to afford
the crude product as a slightly brown oil. Purification via Kugelrohr
distillation afforded 27 (88 mg, 85% yield) as a clear, colorless oil. 1H
NMR δ 5.86 (ddd, J1 ) 9.5 Hz, J2 ) 10.3 Hz, J3 ) 17.0 Hz, 1H), 5.26
(dd, J1 ) 1.7 Hz, J2 ) 17.0 Hz, 1H), 5.15 (dd, J1 ) 1.7 Hz, J2 ) 10.3
Hz, 1H), 2.30 (d, J ) 8.2 Hz, 1H), 2.16 (dd, J1 ) J2 ) 8.8 Hz, 1H),
1.26 (s, 3H), 1.25 (s, 3H); 13C NMR δ 169.0, 130.6, 118.6, 43.1, 42.0,
33.1, 28.1, 14.6. Anal. Calcd for C8H11OCl: C, 60.57; H, 6.99.
Found: C, 60.80; H, 6.98.
Carbene Complex 28. This carbene complex was prepared via a
1
as a clear, colorless oil. The H spectrum was consistent with that
modification of Semmelhack and Lee’s method.7 An airless flask
reported in the literature.24 1H NMR δ trans: 9.53 (d, J ) 3.4 Hz,
1H), 4.12 (m, 2H), 2.40 (m, 2H), 1.30 (s, 3H), 1.26 (s, 3H), 1.23 (t, J
) 7.2 Hz, 3H); cis: 9.70 (d, J ) 6.5 Hz, 1H), 4.12 (m, 2H), 2.08 (d,
J ) 8.7 Hz, 1H), 1.79 (dd, J1 ) 6.5 Hz, J2 ) 6.6 Hz, 1H), 1.56 (s,
3H), 1.24 (t, J ) 7.2 Hz, 3H), 1.23 (s, 3H).
8
containing K2Cr(CO)5 (1.90 mmol) in THF (15 mL) was cooled to
-78 °C. Acid chloride 27 (301 mg, 1.90 mmol) in THF (3 mL) was
added via syringe under argon, and the resultant green-black mixture
was allowed to stir at -78 °C for 20 min. The mixture was warmed
to room temperature over 2 h, and the solvents were removed under
reduced pressure. The residue was taken up in chilled, degassed H2O
Methoxy Lactone 24. This compound was prepared via a slight
modification of the literature procedure.24 To an oven-dried 25-mL
two-necked round-bottomed flask equipped with a stirbar, reflux
condenser, and argon flow was added MeOH (10 mL). Sodium metal
(344 mg, 14.9 mmol) was added in small portions, and the solution
was heated to reflux for 30 min. A solution of 23 (1.25 g, 7.34 mmol)
in MeOH (3 mL) was added via syringe, and the solution was heated
to reflux for 3 h, during which time it became orange/brown in color.
The solution was cooled to 0 °C and 3 N HCl was slowly added to pH
4. The solution was extracted with Et2O (4 × 15 mL), and the
combined organic layers were washed with 5% aqueous NaHCO3 (3
× 15 mL) and H2O (2 × 10 mL), and dried over MgSO4. Filtration
and removal of solvents under reduced pressure afforded the crude
product as a yellow oil. Purification via flash chromatography (SiO2,
4/1 hexanes/EtOAc) afforded 24 (461 mg, 40% yield) as a clear,
-
(20 mL), and Me3O+BF4 (281 mg, 1.90 mmol) was added over 15
min. The solution was filtered through Celite and extracted with
hexanes (5 × 15 mL). The combined organic layers were dried over
MgSO4, filtered, and concentrated to an orange oil. Purification via
flash chromatography (SiO2, hexanes) afforded 28 (346 mg, 55% yield)
as an orange solid. 1H NMR δ 5.95 (ddd, J1 ) 9.5 Hz, J2 ) 10.2 Hz,
J3 ) 17.0 Hz, 1H), 5.14 (dd, J1 ) 1.6 Hz, J2 ) 17.0 Hz, 1H), 5.02 (dd,
J1 ) 1.6 Hz, J2 ) 10.2 Hz, 1H), 4.71 (s, 3H), 3.59 (d, J ) 7.7 Hz,
1H), 2.31 (dd, J1 ) 7.8 Hz, J2 ) 9.3 Hz, 1H), 1.38 (s, 3H), 1.15 (s,
3H); 13C NMR δ 354.2, 223.5, 216.7, 133.0, 116.4, 66.2, 61.3, 49.2,
39.7, 29.6, 15.3; IR (neat) ν 2059, 1918 cm-1; MS 330 (M+).
Cyclopentenone 29. Chromium carbene complex 28 (60 mg, 0.182
mmol) was taken up in CH2Cl2 (7 mL) in an airless flask equipped
with a sidearm. The resultant yellow-orange solution was degassed
(freeze-pump-thaw degassing using liquid N2, 3 cycles) and trans-
ferred to an Ace pressure tube. The pressure tube was charged to 70
psi of CO (3 cycles) and irradiated at 25 °C for 9 h. Solvents were
1
colorless oil. The H NMR was consistent with that reported in the
literature.24 1H NMR δ 5.01 (s, 1H), 3.46 (s, 3H), 2.01 (d, J ) 5.7 Hz,
1H), 1.97 (d, J ) 5.8 Hz, 1H), 1.14 (s, 3H), 1.12 (s, 3H).
Hydroxy Lactone 25. This compound was prepared according to
the literature procedure.24 Methoxy lactone 24 (621 mg, 3.98 mmol)
(30) Ortiz de Montellano, P. R.; Dinzio, S. E. J. Org. Chem. 1978, 43,
(29) Gupta, D.; Somar, R.; Dev, S. Tetrahedron 1982, 38, 3013.
4323.

7880 J. Am. Chem. Soc., Vol. 118, No. 34, 1996
Moser and Hegedus
removed under reduced pressure and the residue was taken up in Et2O
and decanted away from Cr(CO)6. Purification of the organic layers
via flash chromatography (SiO2, 3/1 hexanes/EtOAc) afforded 29 (25
mg, 83% yield) as a clear, colorless oil. 1H NMR δ 6.16 (s, 1H), 5.61
(ddd, J1 ) 9.2 Hz, J2 ) 10.2 Hz, J3 ) 16.9 Hz, 1H), 5.31 (dd, J1 ) 1.1
Hz, J2 ) 10.3 Hz, 1H), 5.20 (dd, J1 ) 0.9 Hz, J2 ) 16.9 Hz, 1H), 3.67
(s, 3H), 2.76 (d, J ) 8.9 Hz, 1H), 1.21 (s, 3H), 1.03 (s, 3H); 13C NMR
δ 201.7, 154.5, 135.5, 131.6, 121.0, 61.8, 56.8, 39.4, 28.7, 26.6; IR
(neat) ν 1721, 1626 cm-1. Anal. Calcd for C10H14O2: C, 72.26; H,
8.49. Found: C, 72.06; H, 8.29.
[(Benzyloxy)(cyclopropyl)carbene]pentacarbonylchromium (0)
(30a). Tetramethylammonium ate complex [(CO)5CrdC(O)CH-
(CH2)2]-NMe4+ 31 (2.00 g, 5.97 mmol) in 30 mL of CH2Cl2 was treated
with acetyl bromide (0.44 mL, 5.97 mmol) at -40 °C, and the resulting
mixture was stirred at -30 °C for 1 h. Benzyl alcohol (0.62 mL, 5.97
mmol) was added, and the mixture was stirred at -30 °C for an
additional 1 h and then warmed to 25 °C. Removal of the solvents
under reduced pressure gave the crude product as a yellow oil.
Purification via flash chromatography (SiO2, hexanes) afforded 30a
(1.67 g, 80% yield) as a yellow solid. 1H NMR δ 7.46-7.38 (m, 5H),
5.94 (s, 2H), 3.53 (m 1H), 1.40 (m, 2H), 1.19 (m, 2H); 13C NMR δ
351.8, 223.5, 216.8, 134.2, 129.1, 128.9, 128.2, 82.3, 41.6, 18.1; IR
(neat) ν 2060, 1908; MS 352 (M+).
Cl2 (7 mL) in an airless flask equipped with a sidearm. The resultant
solution was degassed (freeze-pump-thaw degassing using liquid N2,
3 cycles) and transferred to an Ace pressure tube. The pressure tube
was charged to 80 psi of CO (3 cycles) and irradiated at 25 °C for 5
h. Solvents were then removed under reduced pressure and the residue
was taken up in Et2O and decanted away from Cr(CO)6. Purification
of the organic layers via flash chromatography (SiO2, 3/1 hexanes/
EtOAc) afforded 31a (43 mg, 68% yield) as a white crystalline solid,
mp 62-63 °C. 1H NMR δ 7.35-7.29 (m, 5H), 6.37 (t, J ) 3.0 Hz,
1H), 4.94 (s, 2H), 2.46 (m, 2H), 2.39 (m, 2H); 13C NMR δ 202.4,
156.2, 135.8, 128.7, 128.5, 128.1, 127.4, 71.6, 33.0, 21.9; IR (neat) ν
1716, 1633 cm-1
. Anal. Calcd for C12H12O2: C, 76.57; H, 6.43.
Found: C, 76.70; H, 6.56.
Acknowledgment. Support for this research by National
Science Foundation Grant CHE-9224489 is gratefully acknowl-
edged. Mass spectra were obtained on instruments supported
by the National Institutes of Health shared instrumentation grant
GM49631. Additional research performed by National Science
Foundation Undergraduate Research Participant Molly Dal-
kiewicz is gratefully acknowledged. The authors thank an
anonymous referee for helpful suggestions regarding the struc-
tures and mechanism of formation of 7, 8, and 19 and Dr. Xiao
Yi for carrying out the MM2 calculations to help establish their
structures.
Cyclopentenone 31a. [(Benzyloxy)(cyclopropyl)carbene]pentacar-
bonylchromium(0) (30a) (168 mg, 0.477 mmol) was taken up in CH2-
(31) Prepared according to literature procedure: Fischer, E. O.; Maasbo¨l,
A. Chem. Ber. 1967, 100, 2445.
JA9537585