G. A. Brown et al. / Tetrahedron 56 (2000) 5579±5586
5585
478.1007); m/z (E.I.) (80Se) 478 (M1, 9%); nmax (CH2Cl2)/
cm21 1770, 1746; dH (300 MHz: CD3CN) 0.95 (3H, s, CH3),
1.05 (3H, s, CH3), 1.15 (3H, s, CH3), 1.17±1.45 (6H, m,
3£CH2), 1.94 (1H, quintet, J2.5 Hz, CH), 3.07 (1H, dd,
J15.5, 2.0 Hz, 60b-H), 3.43 (1H, dd, J15.5, 4.0 Hz,
60a-H), 4.71 (1H, s, 20-H), 5.11 (1H, dd, J4.0, 2.0 Hz,
50-H), 5.25 (2H, s, CH2Ar), 7.65 (2H, part of AA0BB0,
J9.0, Ar) and 8.23 (2H, part of AA0BB0, J9.0, Ar).
Due to the small sample available, no 13C NMR data is
available.
J4.0, 2.0 Hz, 5-H), 7.64 (2H, part of AA0BB0, J9.0 Hz,
Ar), 7.68 (2H, part of AA0BB0, J9.0 Hz, Ar) and 8.22
(4H, part of AA0BB0, J9.0 Hz, Ar); dC (75.5 MHz:
CD3CN) 14.2 (CH3), 14.3 (CH3), 23.1 (CH2), 23.2
(CH2), 27.2 (CH3), 31.7 (CH2), 32.0 (CH2), 33.7 (SCH2),
34.4 (SCH2), 34.8 (CH3), 49.5 (6-CH2), 51.3 (6-CH2),
58.3 (5-CH), 58.4 (5-CH), 67.0 (CH2Ar), 67.2 (CH2Ar),
70.6 (2-CH), 72.9 (2-CH), 124.9 (CH), 125.0 (CH),
130.2 (CH), 130.3 (CH), 168.0 (CvO), 168.1 (CvO),
171.6 (CvO) and 171.9 (CvO) (signals due to 2-C
were not observed and the aromatic carbons were not
completely resolved); dSe (57.25 MHz: CD3CN) 539.6
and 568.1.
(2S*,5R*)-7-Oxo-3,3-bis(4-methoxyphenyl)-4-selena-1-
azabicyclo[3.2.1]heptane-2-carboxylic acid PNB ester
7e. A solution of oxazolidinone 1 (0.200 g, 0.65 mmol)
and selenoketone 6e (0.256 g, 0.84 mmol) in MeCN
(5 cm3) [distilled and degassed] was heated at 808C for
21 h in a sealed tube. The solvent was removed in vacuo
and the residue was puri®ed by ¯ash column chromato-
graphy [60H silica gel, 1:9!1:4 EtOAc±P.E. 40±608C] to
give selenopenam 7e (0.0.94 g, 25%) as a pale yellow oil
(Found: M1H1, 563.0886. C27H25N2O7 74Se requires
563.0887); m/z (C.I.) (80Se) 566 (M2H1, 1%); nmax
(CH2Cl2)/cm21 1772, 1751, 1606; dH (300 MHz: C6D6)
2.32 (1H, dd, J16.0, 2.0 Hz, 6b-H), 2.52 (1H, dd,
J16.0, 4.0 Hz, 6a-H), 2.84 (3H, s, OCH3), 2.92 (3H, s,
OCH3), 3.96 (1H, part of AB, J13.0 Hz, CH2Ar), 4.02
(1H, part of AB, J13.0 Hz, CH2Ar), 5.20 (1H, dd,
J4.0, 2.0 Hz, 5-H), 5.58 (1H, s, 2-H), 6.09 (2H, part of
AA0BB0, J9.0 Hz, Ar), 6.17 (2H, part of AA0BB0,
J9.0 Hz, Ar), 6.41 (2H, part of AA0BB0, J9.0 Hz, Ar),
7.10 (2H, part of AA0BB0, J9.0 Hz, Ar), 7.15 (2H, part of
AA0BB0, J9.0 Hz, Ar) and 7.43 (2H, part of AA0BB0,
J9.0 Hz, Ar); dC (75.5 MHz: C6D6) 49.4 (6-CH2), 55.0
(OCH3), 55.2 (OCH3), 57.4 (5-CH), 65.8 (CH2Ar), 68.5
(2-CH), 80.6 (Cquat.), 113.6 (CH), 114.4 (CH), 123.7 (CH),
129.0 (CH), 129.8 (CH), 132.2 (CH), 134.5 (Cipso), 139.8
(Cipso), 141.8 (Cipso), 159.4 (Cipso), 159.6 (Cipso), 168.0
(CvO) and 168.8 (CvO). One signal due to a Cipso was
not observed.
(2S*,3R*5R*) and (2S*,3S*5R*)-7-Oxo-3-methoxy-3-phenyl-
4-selena-1-azabicyclo[3.2.1]heptane-2-carboxylic acid
PNB ester 10b. A solution of oxazolidinone 1 (0.163 g,
0.53 mmol) and selenoester 9b (0.110 g, 0.59 mmol) in
MeCN (5 cm3) [distilled and degassed] was heated at
808C for 13 h in a sealed tube. The solvent was removed
in vacuo and the residue was puri®ed by ¯ash column
chromatography [60H silica gel, 1:9!1:3 EtOAc±P.E.
40±608C] to give selenopenam 10b (0.096 g, 40%) as a
1:2 mixture of isomers (Found: M1, 462.0337.
C20H18N2O6 80Se requires 462.0330); m/z (E.I.) (80Se) 462
(M1, 4%); dC (75.5 MHz: CD3CNÐobtained on mixture
of isomers) 47.1 (6-CH2, minor), 51.8 (6-CH2, major),
54.4 (OCH3, major), 56.9 (5-CH, major), 57.8 (OCH3,
minor), 57.9 (5-CH, minor), 66.8 (CH2Ar, minor), 66.9
(CH2Ar, major), 75.1 (2-CH, minor), 75.3 (2-CH, major),
117.1 (Cquat.), 117.2 (Cquat.), 124.8 (CH), 124.9 (CH),
128.7 (CH), 129.7 (CH), 130.1 (CH), 130.2 (CH),
130.3 (CH), 130.4 (CH), 130.8 (CH), 137.3 (Cipso),
140.3 (Cipso), 143.7 (Cipso), 144.5 (Cipso), 149.2 (Cipso),
150.6 (Cipso), 167.3 (CvO), 167.4 (CvO), 171.8 (CvO)
and 172.4 (CvO);
The major isomer (as determined by NMR) crystallised and
the structure was determined (see text and Fig. 3 where the
numbering system used corresponds to the `penam' conven-
tion where 2-C and 3-C are switched).
(2S*,3R*5R*) and (2S*,3S*5R*)-7-Oxo-3-methyl-3-butyl-
thio-4-selena-1-azabicyclo[3.2.1]heptane-2-carboxylic
acid PNB ester 10a. A solution of oxazolidinone 1 (0.191 g,
0.62 mmol) and selenothio ester 9a (0.125 g, 0.64 mmol)
in MeCN (5 cm3) [distilled and degassed] was heated at
808C for 15 h in a sealed tube. The solvent was removed
in vacuo and the residue was puri®ed by ¯ash column
chromatography [60H silica gel, 0:1!1:4 EtOAc±P.E.
40±608C] to afforded selenopenam 10a (0.130 g, 45%) as
a pale yellow oil and as a 1:1 mixture of isomers which
were not separated. (Found: M1, 458.0424. C18H22N2O5S
80Se requires 458.0414); m/z (E.I.) (80Se) 458 (M1, 15%);
nmax (CH2Cl2)/cm21 1778, 1750, 1608; dH (300 MHz:
CD3CN) 0.81 (3H, t, J7.0 Hz, CH3), 0.89 (3H, t,
J7.0 Hz, CH3), 1.17±1.58 (8H, m, 4£CH2), 1.84 (3H, s,
CH3), 2.07 (3H, s, CH3), 2.53±2.69 (4H, m, 2£SCH2), 3.24
(1H, dd, J16.0, 2.0 Hz, 6b-H), 3.30 (1H, dd, J16.0,
2.0 Hz, 6b-H), 3.70 (1H, dd, J16.0, 4.0 Hz, 6a-H), 3.75
(1H, dd, J16.0, 4.0 Hz, 6a-H), 4.88 (1H, s, 2-H), 4.94 (1H,
s, 2-H), 5.26 (1H, part of AB, J 13.5 Hz, CH2Ar), 5.28 (1H,
part of AB, J13.5 Hz, CH2Ar), 5.33 (1H, part of AB,
J13.5 Hz, CH2Ar), 5.35 (1H, part of AB, J13.5 Hz,
CH2Ar), 5.63 (1H, dd, J4.0, 2.0 Hz, 5-H), 5.65 (1H, dd,
Data for (2Sp,3Rp5Rp) (major) isomer: dH (300 MHz:
CD3CN) 3.30 (1H, dd, J16.0, 1.5 Hz, 6b-H), 3.33 (3H,
s, OCH3), 3.81 (1H, dd, J16.0, 4.0 Hz, 6a-H), 4.83 (1H,
s, 2-H), 5.18 (1H, part of AB, J13.5 Hz, CH2Ar), 5.30 (1H,
part of AB, J13.5 Hz, CH2Ar), 5.61 (1H, dd, J4.0,
1.5 Hz, 5-H), 7.32±7.37 (2H, m, Ar), 7.52 (2H, part of
AA0BB0, J9.0 Hz, Ar), 7.56±7.60 (3H, m, Ar) and 8.21
(2H, part of AA0BB0, J9.0 Hz, Ar); dSe (57.25 MHz:
CDCl3) 507.8.
Data for (2Sp,3Sp5Rp) (minor) isomer (obtained by compar-
ison of NMR data for the mixture with that available from
the pure major isomer): dH (300 MHz: CD3CN) 3.17 (3H, s,
OCH3), 3.27 (1H, dd, J16.0, 2.0 Hz, 6b-H), 3.75 (1H, dd,
J16.0, 4.5 Hz, 6a-H),), 4.62 (1H, part of AB,
J13.5 Hz, CH2Ar), 4.87 (1H, part of AB, J13.5 Hz,
CH2Ar), 5.07 (1H, s, 2-H), 5.74 (1H, dd, J4.5, 2.0 Hz,
5-H), 7.17 (2H, part of AA0BB0 J9.0 Hz, Ar), 7.26±
7.31 (2H, m, Ar), 7.48±7.55 (3H, m, Ar) and 8.10 (2H,
part of AA0BB0, J9.0 Hz, Ar); dSe (95.35 MHz: CDCl3)
396.0.