Solvent‐Free Synthesis of Substituted Benzimidazoles and Quinazolinones via Acceptorless Dehydrogenative Coupling Using Ferrocene‐Hydrazone‐Based Ru(II)‐p–cymene Catalysts

Abstract

A series of ferrocene‐hydrazone based Ru(II)‐p‐cymene complexes were investigated for their catalytic activity towards acceptorless dehydrogenative coupling (ADC) reactions. Ru(II)‐p‐cymene isonicotinic Fc‐hyrazone complex performed better in the solvent‐free synthesis of 1,2‐disubstituted benzimidazoles (up to 88%) and quinazolinones (up to 95%). The catalysis was extended to a wide range of benzylic alcohols. The synthesis of 1,2‐disubstituted benzimidazoles was accomplished with electron‐donating/‐withdrawing o‐phenylenediamines as well. A catalytic structure‐activity relationship was established by varying the steric and electronic parameters on the substrates. All the catalytic experiments exhibited good to moderate yields, with hydrogen and water as the only by‐products. The prepared complexes were well characterized using analytical and spectroscopic techniques. The molecular structures of the ligands and complex were resolved using single crystal X‐ray crystallographic studies.

N-Alkylation of aromatic amines with alcohols by using a commercially available Ru complex under mild conditions

“…47,48 In this scenario, their practical, direct synthesis from primary alcohol and o-phenylenediamine has gained much attention. [49][50][51] However, operating temperatures over 100 °C are required. We then decided to test the o-phenylenediamine in the presence of benzyl alcohol and 1-pentanol (Scheme 4).…”

An Oxidant-Free and Mild Strategy for Quinazolin-4(3H)-One Synthesis via CuAAC/Ring Cleavage Reaction

“…The other method is the condensation of 2-aminobenzoyl derivatives with carbonyl derivatives (Scheme 1a). The latter method is the primary approach; the 2-aminobenzoyl derivatives included are 2-aminobenzamides [13][14][15][16][17][18][19][20][21][22][23][24], 2-aminobenzoic acid [11,[25][26][27], 2-nitrobenzamides [28,29], and methyl anthranilate [30][31][32], while the carbonyl derivatives included are aldehydes [14,15], 1,3-diketones [16,17], orthoesters [18,19], benzyl alcohols [20][21][22], benzyl halides [23,24], acetophenones [33][34][35][36], methylarenes [37], and others [38,39]. Although most of these synthetic methods have their own merits, they often require extreme reaction conditions such as heating, using dehydration reagents, and adding an oxidant, which limits the synthesis of phenolic quinazolin-4(3H)-ones, or the phenol hydroxyl group needs to be protected in advance.…”