Synthesis of dihydrophenanthridines by a sequence of Ugi-4CR and palladium- catalyzed intramolecular C-H functionalization

• Florence Bonnaterre,
• Michèle Bois-Choussy and
• Jieping Zhu

Beilstein J. Org. Chem. 2008, 4, No. 10, doi:10.3762/bjoc.4.10

• . Introduction Multicomponent reactions (MCRs) offer a unique way to generate efficiently libraries of complex molecules with high degree of diversity [1][2]. Among them, the Ugi four component reaction (Ugi-4CR) is without doubt one of the most powerful transformations that has been extensively investigated for

• Scheme 1. The Ugi four-component reaction between an o-iodobenzaldehyde 2, an aniline 3, an isocyanide 4 and a carboxylic acid 5 should afford an α-acetamido-α-phenylacetamide 6, which upon palladium-catalyzed C-H activation process should provide dihydrophenanthridine 1 [15][16][17][18][19][20][21

• temperature afforded the four-component adduct 6a (R1 = R2 = H, R3 = tert-butyl, R4 = n-propyl) in 84% yield. Cyclization of 6a was examined under a variety of conditions and the results are summarized in Table 1. Treatment of 6a under conditions we developed previously for the synthesis of tetracyclic