Synthesis and structures of 1,3,1′,3′-tetrabenzyl-2,2′-biimidazolidinylidenes (electron-rich alkenes), their aminal intermediates and their degradation products

Benzyl (R) substituted enetetramines 9 and 3 have been studied. From HNR(CH2)(2)NRH and CH(NMe2),OBu' or CH(OMe)(2)NMe2, two new intermediates along the pathway to 9, namely the orthoamide 11 and the bis(orthoamide) 12 were isolated. Each of 11 and 12 was converted into 9 by refluxing in toluene, Photolysis of 9 yielded the isomer 10, while thermolysis of 9 gave the di(debenzylated) product 1,1'-dibenzyl-2,2'-biimidazoline 13. A route to 3 (R = R' = CH2Ph) similar to those used for 9, involving the condensation of 1,2-C6H4[N(R)H](2) with CH(OMe)(2)NMe2, or the reaction between 1,3-dibenzylbenzimidazolium chloride 8 (X = Cl) and NaH, did not give the expected enetetramine 3 (the dibenzo-analogue of 9), the bis(debenzylated) product 15 being obtained instead. Heating the orthoamide 1,2-RNC6H4N(R)C(H)NMe2, prepared from CH(NMe2)(2)OBu' and 1,2-C6H4[N(H)R](2), also gave 15, The reactions of S-8, PhNCS or KOH with a mixture of 8 (X = Cl) and NaH gave 17, 18 or 19, respectively, consistent with the transient formation in each reaction of the tetrabenzylenetetramine 3 (R = R' = CH2Ph), The molecular structure of each of the crystalline compounds 10, 11, 12 and 13 was established by X-ray diffraction.