Chlorosulfonyl isocyanate → 2-(4-Oxoazetidin-2-yl)propyl acetate

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Reaction Steps

In words relative to the above diagram for the preparation of 3 (where R2 =H), the 4-(1-substituted-2-acetoxyvinyl)acetidinone-2-one (3') is prepared by reacting, for example (R1 =CH3): chlorosulphonyl isocyanate and acyloxybutadiene (1') such as 1-acetoxy-2-methylbutadiene in a solvent such as anhydrous diethyl ether at a temperature of from about 31 30° C. to 0° C. under a nitrogen atmosphere. The reaction intermediate 2' is converted to 3' by hydrolysis. The reduction of 3' to provide 4-(1-methyl-2-acetoxyethyl)-2-azetidinone (4') is conducted by any convenient means such as hydrogenation in the presence of a catalyst such as platinum, palladium or oxides thereof under a hydrogen pressure of from 1 to 20 atmospheres in a solvent such as ethanol, ethylacetate, or the like at a temperature of from 0° to 25° C. for from 5 minutes to 1 hour. The 4-(2-hydroxy-1-methyl-ethyl)-2-azetidinone species 5' is obtained from 4' by hydrolysis. The 8-oxo-2,2,5-trimethyl-3-oxa-1-azabicyclo[4.2.0]octane species 6' is obtained on treatment of 5' with 2,2-dimethoxypropane in the presence of a catalyst such as boron trifluoride etherate in a solvent such as methylene chloride at a temperature of from 0° to 40° C. for from 1 to 40 minutes. Alkylation of 6' provides 7'. Typically, 6' is treated with a strong base such as lithium diisopropylamide, sodium hydride, phenyl lithium or butyl lithium and the like in a solvent such as tetrahydrofuran (THF), ether, dimethoxyethane, and the like at a temperature of from -80° to 0° C., whereupon the alkylating agent of choice, R6X is added (R6 is as described above and X is chloro or bromo; alternatively, the alkylating agent may be R6 tosylate, R 6 -mesylate or an aldehyde or ketone such as acetaldehyde and the like) to provide mono-alkylated species 7'. When the desired dialkylated species 8' may be obtained from 7' by repeating the alkylating procedure, 6'→7'.

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