Cyclopropanediamines, 4. – Synthesis and ^1^H‐NMR Spectra of Pure Diastereomers of 1,2‐Cyclopropanediamines and 1,2‐Cyclopropanediammonium Dibromides
The efficient preparation of pure diastereomers of N,N′‐(1,2‐cyclopropanediyl)diurethanes 16–18 and ‐diammonium dibromides 4, 19, and 20 is reported. Curtius rearrangement of cis‐ and trans‐1,2‐cyclopropandicarboxylic dihydrazides 14 yields di(O‐benzyl) diurethanes 16 on a 10‐100 g scale. The cis‐1,2‐cyclopropanedicarboxylic dihydrazides cis‐14 tend to form bicyclic products. Thus, from cis‐14a a small amount of 22a is obtained besides the diurethane cis‐16a. Cyclisation is the main reaction in the case of cis‐1,2‐dimethyl‐1,2‐cyclopropanedicarboxylic hydrazide (cis‐14e) which affords the bicyclic products 22e and 24, but no diurethane. The 1,2‐dimethyl‐1,2‐cyclopropanedicarboxylic acid (27) reacts with diphenyl phosphorazidate to produce the monobenzyl ester 29. The diurethanes 16 are methylated (→ 17) and benzylated (→ 18) at both nitrogen atoms. The benzyloxycarbonyl group is removed from the diurethanes 16–18 by the action of hydrogen bromide in acetic acid to yield the 1,2‐cyclopropanediammonium dibromides 4, 19, and 20. The ^1^H‐NMR spectra are analysed and the results are employed as criteria for the configurations. magnified image