Vinyl carbodiimides

The [2+4] diastereoselective annulation of vinyl carbodiimides 48 to cyclic N-alkylimines 49 affords the S,S-diastereomer of the bicyclic dihydropyrimidine 50. This reaction is used in the synthesis of batzelladin alkaloids. 

Vinyl carbodiimides 51 also react with tosyl isocyanate to give [2+4] cycloadducts. When the reaction is conducted at room temperature in acetonitrile, addition across the 0=N bond of the isocyanate occurs to give 52. In contrast, reaction in refluxing benzene (15-30 hours) affords 53, resulting from addition across the C=0 bond of the isocyanate. ... 

Some substituted unsaturated arylcarbodiimides undergo intramolecular cyclization. For example, the vinyl carbodiimide 63 acts as an azadiene to undergo a 6 7r-electrocycli-zation on heating at 140 °C to form an intermediate, which rearomatizes to give 1-amino-isoquinolines 64." ... 

Studies focused on the ability of A -vinyl carbodiimides to undergo cycloaddition reactions have been carried out in recent years (Scheme 56). Thus, 2-azadiene derivatives 245 reacted with tetracyanoethylene to yield dihydropyridines 246 (86CL135), whereas treatment of 245 with... 

Gin returned with an equally impressive synthesis of (-)-crambidine utilizing a variant of the aza-annulation employing thioimidate 59 with vinyl carbodiimide 60 (10JA1802). A rare gold-catalyzed intramolecular alkyne hydroamination of 61 cyclized the third ring of the core affording 62. With the core tricyclic scaffold constructed, four additional steps were required for the completion of the synthesis in a relatively straightforward manner. 

Also, vinyl carbodiimides react as azadienes in the [4+2] cycloaddition reaction. For example, reaction of the vinyl carbodiimide 200 with tetracyanoethylene affords the [4+2] cycloadduct 201. ... 

Perl NR, Ide ND, Prajapati S, Perfect HH, Dur6n SG, Gin DY. Annulation of thioimidates and vinyl carbodiimides to prepare 2-aminopyrimidines, competent nucleophiles for intramolecular alkyne hydroamination. Synthesis of (—)-crambi-dine. J. Am. Chem. Soc. 2010 132(6) 1802-1803. 

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