Cycloaddition reactions of 1,1-enediamines

In this section, we will discuss the few, but interesting, cycloaddition reactions of 1,1-enediamines. These cycloadditions provide a useful synthetic approach to a variety of complex compounds, and reflect the differences between 1,1-enediamines and en-amines on the one hand, and between simple and conjugated 1,1-enediamines on the other. 

Different modes of reaction are known for the reaction of 1,1-enediamines with electrophilic acetylenes. Simple 1,1-enediamines undergo cycloaddition reaction which will be discussed in Section V.A119, whereas conjugated 1,1-enediamines act as nucleophiles towards activated acetylenes. 

A [2 + 2] cycloaddition reaction between simple 1,1-enediamine and a sulfonyl chloride was also observed157-159. In the presence of a base, 1,1-dimorpholinoethy-lene (154) reacted with methanesulfonyl chloride (199) in ether or in tetrahydrofuran to give 3-morpholinothietane 1,1-dioxide (200) in good yield (equation 83). However, the reaction takes a different course in chloroform, leading to the conjugated 1,1-enediamine 201. Other reactants than 154 and 199 did not form cycloaddition products under the same conditions160. 

The only 1,1-enediamines known to react with acyclic dienes in an all-carbon [2 + 4]-cycloaddition are the alkylideneimidazolidines, as has been reported by Heuschmann and Gruseck165,166 in recent years. Thus, cycloaddition products are formed at or below room temperature when 3 is treated with 2,4-dienoates. Hydrolysis of cycloadducts 212 by dilute acid leads to 2-cyclohexenone derivatives 215 or their enol tautomers 216 via 213 and 214 (Scheme 11). The reaction has been extended to... 

The reaction of cyclic 1,1-enediamines 7 and 8 with azides appears interesting. Nitro-substituted 1,1-enediamines 7 reacted with benzenesulfonyl azide to give triazoles 225 in moderate yields. Other secondary 1,1-enediamines analogues gave similar products in comparable yields. The reaction has been postulated to proceed by a sequence of 1,3-cycloaddition to 223, a Dimroth rearrangement to 224 and deamination to 225 (Scheme 12)174. Junjappa and coworkers175 have reported that 1,1-enediamines... 

In contrast to benzenesulfonyl azide, the reaction between 8 and aryl azides gives only a small amount of 226. Instead, highly substituted triazoles 228 are formed as the major products176,177. When 4-nitrophenyl azide is used, the reaction furnishes 228 exclusively. It has been believed that the reaction involves two competitive pathways and benzoyl-substituted 1,1-enediamines 8 act mainly as nucleophiles rather than as 1,3-dipolarophiles toward aryl azides. Consequently, they add to the azide group and, following intramolecular cyclocondensation, give products 228. Only in the case of unfavorable electronic factors does 1,3-cycloaddition reaction to give 226 take place (Scheme 13)177. 

A [2 -f 2] cycloaddition reaction between simple 1,1-enediamine and a sulfonyl chloride was also observed In the presence of a base, 1,1-dimorpholinoethy-... 

Dimethyl acetylenedicarboxylate (80) undergoes initial 1,2 cycloaddition with acyclic enamines to form cyclobutene intermediates which immediately decompose into acyclic dienaminodiesters (94,95). When an acyclic n/c-enediamine is used instead of a simple acyclic enamine, a dienediamino-diester is produced via a cyclobutene intermediate (95a). A cyclization reaction of dimethyl acetylenedicarboxylate with an acyclic enaminoketone... 

In contrast to the cycloaddition of simple 1,1-enediamines, the reaction between conjugated 1,1-enediamines and nitrile oxides proceeds at a slower rate and the yields of products 222 are low (equation 92)172,173. 

---