Bimanes. 14. Synthesis and Properties of 4,6-Bis(carboalkoxy)-1,5-diazabicycloocta-3,6-diene-2,8-diones . Preparation of the Parent syn-Bimane, syn-(Hydrogen,hydrogen)bimane.

Article abstract of DOI:10.1021/jo00341a007

The 3-(carboalkoxy)pyrazolin-5-ones derived from dialkyl oxaloacetates or diethyl α-methyloxaloacetate through reaction with hydrazine can be converted into the strongly fluorescent 4,6-bis(carboalkoxy)-1,5-diazabicyclo<3.3.0>octa-3,6-diene-2,8-diones <4,6-bis(carboalkoxy)-9,10-dioxa-syn bimanes, syn-(COOR,R₁)B (6), R=CH3 or CH3CH2, R₁=CH3, Cl, Br> by base treatment of the corresponding chloro or bromo derivative.The structure of one bis ester, 4,6-bis(carbomethoxy)-3,7-dimethyl-1,5-diazabicyclo<3.3.0>octa-3,6-diene-2,8-dione <6f, syn-(COOCH3,CH3)B>, has beendetermined by X-ray crystallography.Lithium bromide and the esters in CH3CN or DMF yield via dealkylation and decarboxylation the corresponding syn-(H,R₁)B (11), (R₁=H, CH3, Cl, Br, I) or the "mixed" bimanes syn-(EtOOC,R₁)(H,R₁)B (10, R₁=Cl or CH3).A dicarboxylic acid (R₁=CH3; LiBr/CH3CN/60 deg C; two COOCH3's) readily decarboxylates.Hydrogenation of halogenated bimanes over Pd/C(AcOH) replaces one or both halogens, the 2H product from syn-(H,Cl)B being the parent syn-bimane, syn-(H,H)B, syn-(COOR,H)B and ICl yield syn-(COOR,I)B, which gives syn-(H,I)B on dealkylation-decarboxylation.Replacement of Cl in syn-(COOCH2CH3,Cl)B by C6H5S(1-) yields syn-(COOCH2CH3,C6H5S)B.Both ester groups and halogens shift absorption and fluorescence maxima to longer wavelengths than those recorded for syn-(CH3,CH3)B.In 1H NMR spectra, the β-hydrogens of the syn-bimane appear at considerably lower fields (7.52-8.21 ppm) than the α-hydrogens (5.42-6.13 ppm).