The required differentiation of the diacid functionality of compound 7 is achieved by selective lactam formation with the terminal acid to yield the 8-membered lactam 8. A modified Curtius reaction then affords the rearranged diurethane 18 through a series of acyl transfers. Finally,
![Carbamic acid,(4,5,6,7,8,9-hexahydro-5-oxothieno[3,2-b]azocin-3-yl)-, methyl ester (9CI) Structure](https://image.chemsrc.com/caspic/317/59851-15-9.png)
![5-oxo-4,5,6,7,8,9-hexahydro-thieno[3,2-b]azocine-3-carboxylic acid methyl ester Structure](https://image.chemsrc.com/caspic/431/59851-12-6.png)
![5-oxo-4,5,6,7,8,9-hexahydro-thieno[3,2-b]azocine-3-carboxylic acid hydrazide Structure](https://image.chemsrc.com/caspic/393/59851-13-7.png)
