Addition of hexacarbonyldicobalt-stabilized propargyl cations to alkenes

Full text of DOI:10.1021/jo952160c

3912
J . Org. Chem. 1996, 61, 3912-3915
Sch em e 1
Ad d ition of
Hexa ca r bon yld icoba lt-Sta bilized P r op a r gyl
Ca tion s to Alk en es
Marie E. Krafft,* Y. Y. Cheung, Colin Wright, and
Ron Cali
Department of Chemistry, The Florida State University,
Tallahassee, Florida 32306-3006
Received December 5, 1995
Reaction of the hexacarbonyldicobalt-stabilized prop-
argylic cation, the Nicholas cation, with a variety of
nucleophiles is a versatile process which results in the
formation of carbon-heteroatom and carbon-carbon
bonds.1 The list of nucleophiles that react efficiently
includes alcohols,2 hydrides,3 amines,4 sulfonamides,5 and
activated carbon nucleophiles such as allyl silanes,6 silyl
enol ethers,7 enamines,8 and electron rich aromatic rings.9
We have found that hexacarbonyldicobalt-stabilized pro-
pargylic cations react with unactivated alkenes10 to give
a mixture of alkene isomers upon proton loss or, if an
oxygenated functional group is in a position to react with
the resulting cation, lactones or ethers. Heterocycliza-
tions to form lactones generally occur via alkene activa-
tion by reaction with a non-carbon electrophile such as
bromonium ion. In the cyclizations illustrated below, a
carbon electrophile, the Nicholas cation, has been used
to provide an overall one-step carbolactonization11 or
carboalkoxylation.12
Our original goal was to investigate the electrophilic
addition of cation 2, derived from cobalt complex 1, to
an unfunctionalized terminal alkene such as 2-methyl-
1-octene, (3). Treatment of a mixture of cobalt complex
1 and alkene 3 in methylene chloride at 0 °C with BF3‚
Et2O gave, after demetalation using N-methylmorpholine
N-oxide monohydrate (NMO),13 a mixture of regioiso-
meric olefins 4a -c in 53% overall yield. Similar results
were obtained with 1-heptene which furnished olefins 5a
and 5b in 44% overall yield as an approximately 1:1
mixture of alkene regioisomers (Scheme 1). In order to
avoid the formation of olefinic products and to increase
the synthetic utility of this reaction, we used terminal
alkenes bearing oxygen functionality oriented in such a
way that it could trap the putative intermediate carboca-
tion intramolecularly. Initial results with alkenyl meth-
oxymethyl ether 6 gave the corresponding methoxy
alcohol 9 in 20% yield after demetalation. We rational-
ized the formation of 9 as follows (Scheme 2): reaction
of 6 with the cobalt-stabilized cation 2 yields intermediate
(1) Nicholas, K. M. Acc Chem. Res. 1987, 20, 207. Caffyn, A. J . M.;
Nicholas, K. M. In Comprehensive Organometallic Chemistry-II; He-
gedus, L. S., Ed.; Pergamon: Oxford, 1995; Volume 12, p 685. Mukai,
C.; Hanaoka, M. Synlett 1996, 11.
(2) Smit, W. A.; Gybin, A. S.; Shaskov, A. S.; Strychkov, Y. T.;
Kyzmina, L. G.; Mikaelian, G. S.; Caple, R. E.; Swanson, E. D.
Tetrahedron Lett. 1986, 27, 1241. Pandmanabhan, S.; Nicholas, K. M.
Tetrahedron Lett. 1982, 23, 2555.
(3) Nicholas, K. M.; Siegel, J . J . Am. Chem. Soc. 1985, 107, 4999.
(4) Roth, K.-D.; Muller U. Tetrahedron Lett. 1993, 34, 2919.
(5) J eong, N.; Yoo, S. E.; Lee, S. J .; Lee, S. H.; Chung, Y. K.
Tetrahedron Lett. 1991, 32, 2137.
(6) O’Boyle, J . E.; Nicholas, K. M. Tetrahedron Lett. 1980, 21, 1595.
Schreiber, S. L.; Sammakia, T. Crowe, W. E. J . Am. Chem. Soc. 1986,
108, 3128. Tyrell, E.; Heshmati, P.; Sarrazin, L. Synlett 1993, 769.
(7) J u, J .; Reddy, B. R.; Khan, M.; Nicholas, K. M. J . Org. Chem.
1989, 54, 5426. Mukai, C.; Nagami, K.; Hanaoka, M. Tetrahedron Lett.
1989, 30, 5623. Tester, R.; Varghese, V.; Montana, A. M.; Khan, M.;
Nicholas, K. M. J . Org. Chem. 1990, 55, 186. Nicholas, K. M; Mulvaney,
M.; Bayer, M. J . Am. Chem. Soc. 1980, 102, 2508. Mukai, C.; Kataoka,
O.; Hanaoka, M. J . Org. Chem. 1993, 58, 2946. Tyrell, E.; Heshmati,
P.; Sarrazin, L. Synlett 1993, 769.
Sch em e 2
(8) Roth, K.-D. SynLett 1992, 435.
(9) Lockwood, R. F.; Nicholas, K. M. Tetrahedron Lett. 1977, 18,
4163. Grove, D. D.; Miskevich, F.; Smith, C. C.; Corte, J . R. Tetrahedron
Lett. 1990, 31, 6277.
(10) For an example of an aliphatic Friedel Crafts alkene alkylation,
see: Mayr, H.; Striepe, W. J . Org. Chem. 1983, 48, 1159.
(11) For an example of a two-step carbolactonization, see: Burke,
S. D.; Fobare, W. F.; Armistead, D. M. J . Org. Chem. 1982, 47, 3348.
(12) For an example of an intramolecular carboalkoxylation, see:
Hoye, T. R.; Kurth, M. J . J . Org. Chem. 1978, 43, 3693.
(13) NMO monohydrate was prepared from N-methylmorpholine:
VanRheenen, V.; Cha, D. Y.; Hartley, W. M. Organic Syntheses;
Wiley: New York, 1988; Coll. Vol. VI, p 342. N-Methylmorpholine
N-oxide monohydrate exhibits a sharp melting point at 75 °C. Purifica-
tion of the N-oxide by precipitation from acetone (2×), as described in
the Organic Synthesis procedure, gives highly crystalline monohydrate.
S0022-3263(95)02160-8 CCC: $12.00 © 1996 American Chemical Society

Notes
J . Org. Chem., Vol. 61, No. 11, 1996 3913
Ta ble 1. Rea ction of Hexa ca r bon yld icoba lt-Sta bilized
P r op a r gylic Ca tion s w ith Alk en yl Aceta tes
Ta ble 2. Rea ction of Hexa ca r bon yld icoba lt-Sta bilized
P r op a r gylic Ca tion s w ith Alk en yl Acid s a n d Ester s
entry
R1
n
R2
Ac
H/Ac
H/Ac
H
% yieldd
product
1
2
3
4
10a
10b
10c
10d
Me
Me
Me
H
0
1
2
1
47b
54a,c
0
12a
12b/12b′
entry
R1
R2 R3
R4
n
product % yieldd
1
2
3
4
5
6
7
8
9
13a TMS
13b TMS
13c TMS
13d TMS
13e TMS
13f TMS
13g TMS
13h TMS
H
H
H
H
H
H
H
H
H
H
Me CH2CH2TMS
1
1
1
1
2
2
2
2
1
1
1
15a
15a
15b
15b
15c
15c
15d
15d
15e
15f
15g
65a
82a
20
37
53b
40
2
7a
12d
Me
H
H
H
a
b
CH2CH2TMS
H
Demetalation with ceric ammonium nitrate. Demetalation
with NMO‚H2O. c 12b, R2 ) H, 29%; 12b′, R2 ) Ac, 25%. Yields
refer to isolated, chromatographed material.
d
Me CH2CH2TMS
Me
H
H
H
CH2CH2TMS
H
7, subsequent trapping of 7 by the remote oxygen of the
methoxymethyl ether14 gives the cyclic intermediate 8
which is then hydrolyzed upon workup. To demonstrate
that the resulting methyl ether most likely came from
the original methoxymethyl ether protecting group, ad-
dition of EtOH to the reaction mixture prior to workup
yielded methyl ether 9. Our next goal was to establish
which oxygenated functional groups would be most
effective as intramolecular trapping agents.
To evaluate the efficiency of the process we chose
alkenyl acetates 10a -d and alkenyl esters or acids
13a -k which would proceed through the intermediacy
of cations 11 and 14, respectively, upon trapping of the
initially formed cation. The results of these reactions are
summarized in Tables 1 and 2.
6
13i
13j Et
13k
H
Me CH2CH2TMS
Me CH2CH2TMS
52
49
41c
10
11
H
Me Me CH2CH2TMS
a
b
5-15% of 16 was also formed. Using 2 equiv of cobalt
complex and 2 equiv of BF3‚OEt2. c Isolated as a mixture of
diastereomers. Yields refer to isolated, chromatographed mate-
rial.
d
are formed more efficiently than six-membered lactones
(entries 5-8) regardless of whether the incipient cation
is secondary or tertiary. The results of these lactoniza-
tions also suggest that, for best results, the intermediate
carbocation should be tertiary (R3 ) Me) for formation
of both five- and six-membered lactones. In addition,
t
modification of the ester alkyl group (Me, Et, Bu) had
little effect on the yield of lactone 15. From separate
experiments we noted that, for the trimethylsilylethyl
esters, hydrolysis to the corresponding acid did not occur
at any appreciable rate under the reaction conditions. We
therefore concluded that cyclization, in the case of the
TMS ethyl esters, most likely occurs via the ester, not
the corresponding acid.
Furthermore, we have synthesized other oxygen het-
erocycles such as carbonates 18 and 19 and furan 21 by
modification of the trapping functionality on the alkene
(Scheme 3). Methoxymethyl ethers are a poor choice as
trapping agents, and low yields were obtained in the
corresponding coupling/cyclization processes, i.e. 20 to 21
in Scheme 3 and 6 to 9 in Scheme 2.
The yields for the “Nicholas reaction” with allylic and
homoallylic acetates where R1 ) Me (entries 1 and 2,
Table 1) suggest there is little difference in the efficiency
of reactions which proceed via five- and six-membered
cyclic transition states. With the bishomoallylic acetate
10c no products corresponding to intramolecular trapping
of the intermediate carbocation were observed; instead,
a mixture of olefinic products was isolated as in the case
of reaction with 2-methyl-1-octene (Scheme 1). This
result is not surprising since trapping of the correspond-
ing intermediate carbocation would lead to the formation
of a seven-membered cyclic intermediate. With the
homoallylic acetate 10d (where R1 ) H), the reaction
proceeded in very poor yield which is attributed to the
intermediate carbocation being secondary.
In summary, we have established some of the struc-
tural features of the olefinic substrate that are required
for successful carbon-carbon bond formation between
hexacarbonyldicobalt-stabilized propargylic cations and
unactivated alkenes.
Reaction of cobalt complex 1 with alkenes 13a -k gave
a series of lactones 15a -g, and, where R3 ) Me and n )
1 (entries 1 and 2), small amounts of lactone 16 from
protolactonization. Results in Table 2 indicate that, in
general, five-membered lactones (entries 1-4 and 9-11)
Exp er im en ta l Section
(14) For examples of participation by internal nucleophiles, see:
Muks, E.; Loiveke, I.; Pehk, T. Tetrahedron Lett. 1993, 34, 4717. Wipf,
P.; Xu, W. J . Org. Chem. 1993, 58, 5880. Mikami, K.; Shimizu, M.
Tetrahedron Lett. 1992, 33, 6315. Gopalan, A. S.; Prieto, R.; Mueller,
B.; Peters, D. Tetrahedron Lett. 1992, 33, 1679. Miura, K.; Okajima,
S.; Hondo, T.; Hosomi, A. Tetrahedron Lett. 1995, 36, 1483.
(15) Krafft, M. E.; Scott, I. L.; Romero, R. H.; Feibelmann, S.; Van
Pelt, C. E. J . Am. Chem. Soc. 1993, 115, 7199-7207.
Gen er a l P r oced u r e. For general information and prepara-
tion of the hexacarbonyldicobalt alkyne complexes, see reference
15. All cobalt complexes were filtered through a plug of Celite
with low boiling petroleum ethers immediately before use. To
a
stirred solution of cobalt complex (1 mmol) and alkene
substrate (1 mmol) in dry methylene chloride (10 mL) under
nitrogen at 0 °C was added dry boron trifluoride etherate (1.1

3914 J . Org. Chem., Vol. 61, No. 11, 1996
Notes
4.2 Hz, 1H, CHHOH), 2.38 (ABdd, J AB ) 17.4, J ) 7.3, 7.3 Hz,
1H, CtCCHH), 2.36 (ABdd, J AB ) 17.4, J ) 8.3, 6.7 Hz, 1H,
CtCCHH), 1.87 (ddd, J )14.0, 7.8, 7.8 Hz, 1H, CtCCH2CHH),
1.81 (ddd, J ) 14.5, 7.8, 4.2 Hz, 1H, CHHCH2OH), 1.73 (ddd, J
)14.0, 7.8, 6.2 Hz, 1H, CtCCH2CHH), 1.67 (ddd, J )14.5, 6.7,
4.2 Hz, 1H, CHHCH2OH), 1.27 (s, 3H, CH3), 0.14 (s, 9H,
Si(CH3)3).
Sch em e 3
12d : 1H NMR (500 MHz, CDCl3) δ 4.02 (dddd, J ) 12.4, 7.8,
5.2, 5.2 Hz, 1H, CHOH), 3.88 (ABdd, J AB ) 10.9, J ) 5.2, 5.2
Hz, 1H, CHHOH), 3.87 (ABdd, J AB ) 10.9, J ) 5.7, 5.7 Hz, 1H,
CHHOH), 2.39 (ABdd, J ) 17.2, 14.3, 7.0 Hz, 1H, CtCHH), 2.36
(ABdd, J ) 17.2, 14.0, 6.7 Hz, 1H, CtCHH), 1.72 (m, 4H, CH2-
CH2OH, CtCCH2CH2), 0.15 (s, 9H, Si(CH3)3).
1
15a : H NMR (500 MHz, CDCl3) δ 2.625 (ABdd, J AB ) 18.2,
J ) 8.3, 8.3 Hz, 1H, CHHCO2), 2.617 (ABdd, J AB ) 18.2, J )
7.1, 7.1 Hz, 1H, CHHCO2), 2.37 (ABdd, J AB ) 17.1, J ) 8.8, 6.2
Hz, 1H, CtCCHH), 2.35 (ABdd, J AB ) 17.1, J ) 8.3, 6.8 Hz,
1H, CtCCHH), 2.20 (ABdd, J AB ) 13.0, J ) 9.3, 8.3 Hz, 1H,
CHHCH2CO2), 2.00 (ABdd, J AB ) 13.0, J ) 9.3, 6.8 Hz, 1H,
CHHCH2CO2), 1.95 (ABdd, J AB ) 14.0, J ) 7.8, 7.8 Hz, 1H,
CtCCH2CHH), 1.93 (ABdd, J AB ) 14.0, J ) 8.3, 8.3 Hz, 1H,
CtCCH2CHH), 1.40 (s, 3H, CH3), 0.14 (s, 9H, Si(CH3)3).
15b: 1H NMR (500 MHz, C6D6) δ 3.89 (dddd, J ) 7.8, 7.8, 6.5,
4.7 Hz, 1H, CHOCO), 2.04 (dd, J ) 7.8, 6.8, 2H, CH2CO2), 1.77
(ddd, J ) 17.6, 9.9, 4.7 Hz, 1H, CtCCHH), 1.66 (ddd, J ) 17.1,
9.3, 9.3 Hz, 1H, CtCCHH), 1.34 (dddd, J ) 14.0, 8.8, 6.8, 6.8
Hz, 1H, CHHCH2CO2), 1.22 (obscured dddd, J ) 13.0, 8.3, 6.8,
4.7 Hz, 1H, CtCCH2CHH), 1.18 (dddd, J ) 14.0, 7.7, 7.7, 4.7
Hz, 1H, CHHCH2CO2), 0.82 (dddd, J ) 12.4, 9.3, 9.3, 7.8 Hz,
1H, CtCCH2CHH), 0.20 (s, 9H, Si(CH3)3).
mmol). The reaction was monitored by TLC and upon comple-
tion the reaction was quenched with saturated sodium bicarbon-
ate and extracted with methylene chloride (3×). The combined
organic layers were dried over MgSO4, and the solvent was
removed in vacuo. The crude reaction product was demetalated
using either of two procedures. N-Meth ylm or p h olin e N-
Oxid e Mon oh yd r a te: To the reaction mixture in dry THF (20
mL) under nitrogen was added NMO‚H2O (10 mmol) in one
portion, and the reaction was monitored by TLC. When the
reaction was complete, the reaction mixture was filtered through
a plug of silica gel eluting with a 1:1 mixture of hexane and ethyl
acetate. The solvent was removed in vacuo, and the crude
product was purified by silica gel chromatography. Cer ic
Am m on iu m Nitr a te:7 To the stirred reaction mixture and
triethylamine (1 mmol) in acetone (20 mL) under nitrogen was
added ceric ammonium nitrate (5 × 0.8 mmol) every 5 min, and
the reaction was monitored by TLC. When the reaction was
complete, the reaction mixture was concentrated and the residue
was treated with saturated sodium bicarbonate and extracted
with ethyl acetate (3×). The organic layers were combined and
dried over MgSO4. The solvent was removed in vacuo, and the
crude product was purified by silica gel chromatography. All
yields in Tables 1 and 2 refer to isolated, chromatographed
materials. Many of the products were volatile, thus, the yields
are lower than the actual reaction efficiency. Unless otherwise
noted, i.e. by the presence of a mp, all compounds were liquids.
P r oton NMR d a ta :
15c: 1H NMR (500 MHz, C6D6) δ 2.18 (ddd, J )17.1, 10.4, 5.7
Hz, 1H, CtCCHH), 2.05 (ddd, J ) 16.1, 9.9, 6.2 Hz, 1H,
CtCCHH), 1.97 (br dt, J ) 18.2, 6.2 Hz, 1H, CHHCO2), 1.87
(br dt, J ) 18.3, 7.3 Hz, 1H, CHHCO2), 1.60 (ddd, J ) 14.0, 10.4,
5.7 Hz, 1H, CtCCH2CHH), 1.48 (ddd, J ) 14, 10.2, 6.2 Hz, 1H,
CtCCH2CHH) 1.00 (br m, 3H, CHHCH2CO2), 0.84 (br m, 1H,
CHHCH2CO2), 0.81 (s, 3H, CH3), 0.22 (s, 9H, Si(CH3)3).
15d : 1H NMR (500 MHz, CDCl3) δ 4.52 (dddd, J ) 7.8, 7.8,
5.1, 5.1 Hz, 1H, CHOCO), 2.55 (ABd, J AB ) 17.1, J ) 9.6 Hz,
1H, CHHCO2), 2.54 (ABd, J AB ) 17.1, 8.3 Hz, 1H, CHHCO2),
2.35 (ddddd, J ) 12.6, 7.5, 6.5, 6.1, 1.4 Hz, 1H, CHHCH2CH2-
CO2), 1.95-1.65 (m, 6H, CHHCH2CH2CO2, CtCCH2CHH), 1.62
(dddd, J ) 13.1, 7.9, 6.0, 2.1 Hz, 1H, CtCCH2CHH), 0.14 (s,
9H, Si(CH3)3).
15e: 1H NMR (500 MHz, CDCl3) δ 2.64 (ABdd, J AB ) 18.1, J
) 9.3, 7.8 Hz, 1H, CHHCO2), 2.62 (ABdd, J AB ) 18.1, J ) 9.2,
6.1 Hz, 1H, CHHCO2), 2.34 (ABddd, J AB ) 17.1, J ) 8.8, 6.2,
3.0 Hz, 1H, HCtCCHH), 2.32 (ABddd, J AB ) 17.1, J ) 9.5, 5.0,
3.0 Hz, 1H, HCtCCHH), 2.18 (ddd, J ) 13.0, 9.3, 8.3 Hz, 1H,
CHHCH2CO2), 2.02 (ddd, J ) 13.0, 9.3, 5.6 Hz, 1H, CHHCH2-
CO2), 1.97 (partly obscured, br t, J ) 3 Hz, HCtCCH2), 1.96
(partly obscured, ABdd, J AB )14.5, J ) 8.3, 8.3 Hz, 1H,
HCtCCH2CHH), 1.95 (partly obscured, ABdd, J AB )14.5, J )
8.8, 8.8 Hz, 1H, HCtCCH2CHH), 1.41 (s, 3H, CH3).
9: 1H NMR (500 MHz, CDCl3) δ 3.82 (ddd, J )11.2, 8.0, 4.7
Hz, 1H, CHHOH), 3.74 (ddd, J ) 11.2, 5.8, 5.1 Hz, 1H, CHHOH),
3.19, (s, 3H, OCH3), 2.26, (ABdd, J AB ) 17.0, J ) 9.4, 6.5 Hz,
1H, CtCCHH), 2.24 (ABdd, J AB ) 17.0, J ) 9.4, 6.2 Hz, 1H,
CtCCHH), 1.87 (ddd, J ) 14.1, 8.0, 5.1 Hz, 1H, CHHCH2OH),
1.85 (obscured ABdd, J AB ) 14.5, J ) 9.4, 6.5 Hz, 1H,
CtCCH2CHH), 1.77 (ABdd, J AB ) 14.5, J ) 9.8, 6.9 Hz, 1H,
CtCCH2CHH), 1.60 (ddd, J ) 14.5, 5.8, 4.5 Hz, 1H, CHHCH2-
OH), 1.21 (s, 3H, CH3), 0.14 (s, 9H, Si(CH3)3).
1
15f: H NMR (500 MHz, CDCl3) δ 2.62 (ABdd, J AB ) 18.2, J
) 8.3, 8.3 Hz, 1H, CHHCO2), 2.60 (ABdd, J AB ) 18.2, J ) 7.3,
7.3 Hz, 1H, CHHCO2), 2.28 (ABddt, J AB ) 14.5, J ) 9.6, 6.8, 2.6
Hz, 1H, EtCtCCHH), 2.27 (ABddt, J AB ) 14.5, J ) 9.6, 6.8, 2.6
Hz, 1H, EtCtCCHH), 2.20 (ddd, J ) 13.0, 8.3, 8.3 Hz, 1H,
CHHCH2CO2), 2.14 (qt, J ) 7.3, 2.6 Hz, 2H, CH3CH2), 1.99 (ddd,
J ) 13.0, 9.3, 7.6 Hz, 1H, CHHCH2CO2), 1.91 (ABdd, J AB ) 14.2,
J ) 7.8, 7.8 Hz, 1H, EtCtCCH2CHH), 1.89 (ABdd, J AB ) 14.2,
J ) 8.3, 8.3 Hz, 1H, EtCtCCH2CHH), 1.40 (s, 3H, CH3), 1.10
(t, J ) 7.3 Hz, 3H, CH3CH2).
12a : 1H NMR (500 MHz, CDCl3) δ 3.99 (s, 2H, CH2OAc), 2.38
(ABdd, J AB ) 17.1, J ) 8.3, 6.7 Hz, 1H, CtCCHH), 2.36 (ABdd,
J AB ) 17.1, J ) 7.8, 6.8 Hz, 1H, CtCCHH), 2.11 (s, 3H,
OCOCH3), 1.82 (ABdd, J AB ) 14.5, J ) 8.3, 7.3 Hz, 1H,
CtCCH2CHH), 1.74 (ABdd, J AB ) 14.0, J ) 8.3, 7.3 Hz, 1H,
CtCCH2CHH), 1.22 (s, 3H, CH3), 0.14 (s, 9H, Si(CH3)3).
12b′: 1H NMR (500 MHz, CDCl3) δ 4.24 (t, J ) 6.8 Hz, 2H,
CH2OAc), 2.37 (ABdd, J AB ) 17.0, J ) 9.3, 7.3 Hz, 1H,
CtCCHH), 2.35 (ABdd, J AB ) 17.0, J ) 7.0, 7.0 Hz, 1H,
CtCCHH), 2.05 (s, 3H, COCH3), 1.86 (ABdd, J AB ) 14, J ) 7.3,
6.7 Hz, 1H, CHHCH2OAc), 1.84 (ABdd, J AB ) 14, J ) 7.3, 6.7
Hz, 1H, CHHCH2OAc), 1.76 (ABdd, J AB ) 14.0, J ) 7.3, 7.3 Hz,
1H, CtCCH2CHH), 1.75 (ABdd, J AB ) 14.0, J ) 7.8, 7.8 Hz,
1H, CtCCH2CHH), 1.23 (s, 3H, CH3), 0.14 (s, 9H, Si(CH3)3).
12b: 1H NMR (500 MHz, CDCl3) δ 3.93 (ABdd, J AB ) 10.9, J
) 7.8, 4.2 Hz, 1H, CHHOH), 3.88 (ABdd, J AB ) 10.9, J ) 6.2,
18: 1H NMR (500 MHz, CDCl3) δ 4.40 (d, J ) 8.3 Hz, 1H,
CHHOCO2), 4.12 (d, J ) 8.3 Hz, 1H, CHHOCO2), 2.41 (ABdd,
J AB ) 17.1, J ) 7.3, 6.2 Hz, 1H, CtCCHH), 2.39 (ABdd, J AB
)
17.1, J ) 7.8, 7.8 Hz, 1H, CtCCHH), 2.03 (ABdd, J AB ) 14.5, J
) 7.8, 7.8 Hz, 1H, CtCCH2CHH), 2.02 (ABdd, J AB ) 14.5, J )
8.3, 6.7 Hz, 1H, CtCCH2CHH), 1.53 (s, 3H, CH3), 0.15 (s, 9H,
Si(CH3)3).
19: 1H NMR (500 MHz, CDCl3) δ 4.45 (ABdd, J AB ) 11.4, J )
5.5, 5.5 Hz, 1H, CHHOCO2), 4.43 (ABdd, J AB ) 11.4, J ) 7.7,
4.8 Hz, 1H, CHHOCO2), 2.41 (ABdd, J AB ) 17.2, J ) 8.8, 6.6
Hz, 1H, CtCCHH), 2.29 (ABdd, J AB ) 17.2, J ) 8.4, 7.3 Hz,
1H, CtCCHH), 2.12 (ddd, J ) 13.9, 7.6, 5.7 Hz, 1H, CHHCH2-
OCO2), 2.02 (ABdd, J AB
CtCCH2CHH), 2.00 (ABdd, J AB ) 14.3, J ) 8.8, 6.2 Hz, 1H,
) 14.3, J ) 8.4, 6.2 Hz, 1H,

Notes
J . Org. Chem., Vol. 61, No. 11, 1996 3915
CtCCH2CHH), 1.96 (obscured ddd, J ) 14.0, 5.5, 5.5 Hz, 1H,
CHHCH2OCO2), 1.47 (s, 3H, CH3), 0.14 (s, 9H, Si(CH3)3).
21: 1H NMR (500 MHz, CDCl3) δ 3.82 (ABdd, J AB ) 15.0, J )
8.8, 6.2 Hz, 1H, CHHO), 3.80 (ABdd, J AB ) 15.6, J ) 8.3, 7.3
Hz, 1H, CHHO), 2.30 (ABdd, J AB ) 16.6, J ) 9.3, 6.7 Hz, 1H,
CtCCHH), 2.28 (ABdd, J AB ) 16.6, J ) 8.8, 6.7 Hz, 1H,
CtCCHH), 1.93 (ABdddd, J AB ) 18.5, J ) 12.7, 12.7, 7.0, 7.0
Hz, CHHCH2O), 1.90 (ABdddd, J AB ) 18.5, J ) 11.9, 11.9, 6.2,
6.2 Hz, CHHCH2O), 1.78 (ddd, J )12.4, 9.0, 6.7 Hz, 1H,
CHHCH2CH2O), 1.76 (obscured ABdd, J AB ) 13.5, J ) 8.8, 6.2
Hz, 1H, CtCCH2CHH), 1.74 (ABdd, J AB ) 13.5, J ) 8.8, 6.2
Hz, 1H, CtCCH2CHH), 1.64 (ddd, J ) 12.4, 8.8, 6.2, 1H,
CHHCH2CH2O), 1.18 (s, 3H, CH3), 0.14 (s, 9H, Si(CH3)3).
Ack n ow led gm en t. This work has been partially
supported by the National Science Foundation, the
National Institutes of Health, and the Dreyfus Founda-
tion.
Su p p or tin g In for m a tion Ava ila ble: Complete charac-
terization data (2 pages). This material is contained in
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J O952160C