Benzyl 2-[4(R)-(Prop-2-enylsulfonyl-3(S)-chloro-2-oxoazetidinyl-1]-2(isopropyliden)acetate (4e)
and Benzyl 2-[4(R)-(trans-Prop-1-enylsulfonyl-3(S)-chloro-2-oxoazetidinyl-1]-2(isopropyliden)acetate (4f).
The mixture of isomers was obtained by the interaction of 1b and 3c in 23% yield. According to HPLC
(Ultrasphere Si, 20:80 chloroform–hexane) the ratio of 4e to 4f is 1:3, their overall content in the substance
isolated was >97%. Found, %: C 54.54; H 4.99; N 3.76. C18H20NO5S. Calculated, %: C 54.34; H 5.07; N 3.52.
1H NMR spectrum (CDCl3), δ, ppm (J, Hz): 4e: 2.09 (3H, s, CH3); 2.31 (3H, s, CH3); 3.42-3.74 (2H, m,
CH2-allyl); 4.88 (1H, d, J = 2, 4-H); 5.01 (1H, d, J = 2, 3-H); 5.24-5.44 (4H, m, CH2Ph, =CH2); 5.44-5.80 (1H,
m, CH-allyl); 7.33 (5H, s, C6H5). 4f: 1.84 (3H, dd, J = 7, J = 1.6, CH3 propenyl); 2.06 (3H, s, CH3); 2.27 (3H, s,
CH3); 4.88 (1H, d, J = 2, 4-H); 5.01 (1H, d, J = 2, 3-H); 5.11 and 5.33 (2H, AB-system, J = 12, CH2Ph); 5.90
(1H, dd, J = 14, J = 1.6, 1-H propenyl); 6.82 (1H, dd, J = 14, J = 7, 2-H propenyl); 7.33 (5H, s, C6H5).
Benzyl
2-[3-tert-Butoxycarbonylamino-4(R)-(methylsulfonyl)-2-oxoazetidinyl-1]-2-(isopropyliden)-
1
acetate (4g) was obtained as an amorphous substance from the reaction of 1b and 3a in 40% yield. H NMR
spectrum (CDCl3), δ, ppm (J, Hz): 1.46 (9H, s, t -Bu); 2.07 (3H, s, CH3); 2.31 (3H, s, CH3); 2.71 (3H, s,
SO2CH3); 5.02 (1H, br. s, 4-H); 5.09 (1H, br. s, 3-H); 5.15 and 5.40 (2H, AB-system, J = 12, CH2Ph); 5.65-5.75
(1H, m, NH); 7.40 (5H, s, C6H5). Found, %: C 55.87; H 6.32; N 6.30. C28H20N2O7S. Calculated, %: C 55.74;
H 6.24; N 6.19.
Benzyl 2-[3(R)-Amino-4(R)-methylsulfonyl-2-oxazetidinyl-1]-2-(isopropyliden)acetate (4h) and
Benzyl 2-[3(S)-Amino-4(R)-methylsulfonyl-2-oxazetidinyl-1]-2-(isopropyliden)acetate (4i). Compound 4g
(650 mg, 1.43 mmol) was dissolved at 0°C in dichloromethane (2 ml) and trifluoroacetic acid (3 ml). The
solution was stirred for 2 h at 0°C and for 1 h at room temperature, diluted with dichloromethane (70 ml),
washed with 5% potassium carbonate (50 ml) until neutral, with water, and then dried over anhydrous Na2SO4.
The solvent was removed at reduced pressure and the residue was fractionated by column chromatography with
1
ethyl acetate as eluent. The fraction with Rf 0.48 contained ester 4h (100 mg, 20%); mp 90-92°C. H NMR
spectrum (CDCl3), δ, ppm (J, Hz): 2.06 (2H, br. s, NH2); 2.15 (3H, s, CH3); 2.26 (3H, s, CH3); 2.88 (3H, s,
SO2CH3); 4.53 (1H, d, J = 5, 4-H); 4.95 (1H, d, J = 5, 3-H); 5.11, 5.31 (2H, AB-system, J = 13, CH2Ph); 7.37
(5H, s, C6H5). Found, %: C 54.81; H 5.62; N 7.60. C16H20N2O5S. Calculated, %: C 54.53; H 5.72; N 7.95.
The fractions with Rf 0.31 contained ester 4i (51 mg, 10%) as an oily substance, 98% pure according to
HPLC (Zorbax RxC18, mobile phase 45:55 acetonitrile-water). 1H NMR spectrum (CDCl3), δ, ppm (J, Hz): 1.69
(2H, br. s, NH2); 2.04 (3H, s, CH3); 2.26 (3H, s, CH3); 2.66 (3H, s, SO2CH3); 4.57 (1H, d, J = 2, 4-H); 4.66 (1H,
d, J = 2, 3-H); 5.11 and 5.33 (2H, AB-system, J = 13, CH2Ph); 7.37 (5H, s, C6H5).
4-Sulfonylthio-substituted Azetidinones-2 8a-d. Silver nitrate (105 mg, 0.5 mmol) was added to
benzhydryl 2-[4-(2-benzothiazolyldithio)-2-oxoazetidinyl-1]-2-(isopropenyl)acetate (0.5 mmol) (6a) in 9:1
acetone–water (5 ml), the mixture was stirred for 30 min at room temperature and then a sodium sulfinate 7a-d
(0.5 mmol) in 9:1 acetone–water (5 ml) was added. The mixture was stirred for 2 h at room temperature and then
filtered through of Celite. The filtrate was dried over anhydrous Na2SO4. The solvent was evaporated under
reduced pressure and the residue was fractionated on a silica gel column with 3:2 ethyl acetate–hexane as eluent.
The fractions containing the desired product were collected and evaporated.
Benzhydryl 2-(4-Methylsulfonylthio-2-oxoazetidinyl-1]-2-(isopropenyl)acetate (8a) was obtained as
an amorphous substance from the interaction of compounds 6a and 7a in 21% yield. 1H NMR spectrum (CDCl3),
δ, ppm (J, Hz): 1.88 (3H, s, CH3); 3.24 (1H, dd, J = 16, J = 2, 3-H, trans); 3.31 (3H, s, SO2CH3); 3.71 (1H, dd, J
= 16, J = 5, 3-H cis); 4.93 (2H, d, J = 7, =CH2); 5.11 (1H, d, J = 1, NCHCOO); 5.68 (1H, dd, J = 5, J = 2, 4-H);
7.00 (1H, s, CHPh2); 7.35 (10H, s, 2C6H5). Found, %: C 59.46; H 5.37; N 3.16. C22H23NO5S2. Calculated, %: C
59.30; H 5.20; N 3.14.
Benzhydryl 2-[4-(4-Tolylsulfonylthio-2-oxoazetidinyl-1]-2-(isopropenyl)acetate (8b) was obtained as
an amorphous substance from the interaction of compounds 6a and 7b in 35% yield. 1H NMR spectrum (CDCl3),
δ, ppm (J, Hz): 1.62 (3H, s, CH3); 2.31 (3H, s, CH3Ph); 2.91 (1H, dd, J = 2, J = 16, 3-H trans); 3.53 (1H, dd, J
=16, J = 5, 3-H cis); 4.66 (2H, d, J = 7, =CH2); 4.89 (1H, d, J = 1, NCHCOO); 5.37 (1H, dd, J = 5,
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