Cyclic carbodiimide isomers

A study directed to obtain evidence for the interrelationships between het-arylnitrenes, their ring-expanded cyclic carbodiimide isomers, and ring-opened nitrile ylides (Scheme 69) and a review of cumulene rearrangements of ketene-ketene, isocyanate-isocyanate, thioketene-ketene, imidoylketene-ketenimine,... 

Cyclic carbodiimide 48 theoretically exists as two conformational isomers. Comparison of the coupling constant values, calculated using AMI Hamiltonian and Karplus relationship, with the experimental vicinal coupling constants of 8.33 and 1.05 Hz, undoubtedly prove its methyl-out structure 48 <1996JOC4289>. 

The addition of sulphur to the phosphorus analogue 186 of a carbodiimide (Ar = 2,4,6-tri-r rr-butylphenyl) in the presence of dbu produces both the cw-187 and trans- %9 isomers of the 2,4-diaryl-1,2,4-thiadiphosphetane 2,4-disulphide, together with the trans form of the 1,2,3,5-dithiadiphospholane 3,5-disulphide, 190, the last structure being confirmed by single-crystal X-ray analysis Under wet conditions, the system also provided the cw-l,2,4-oxadiphosphetane 188, a structure also confirmed by X-ray analysis. The mode of formation of a cyclic anhydrosulphide 191 (a 1,2,5-thiadiphospholane 2,5-disulphide) is indicated in Scheme 55 (Im=l-imidazolyl) . ... 

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