Efficient cobalt(ii) phthalocyanine-catalyzed reduction of flavones with sodium borohydride

Abstract

Efficient and facile reductions of flavones with sodium borohydride (NaBH4) catalyzed by cobalt(II) phthalocyanines afford cis-flavan-4-ols in 89-97% yields.

Highly Chemo‐ and Regioselective Reduction of Aromatic Nitro Compounds Catalyzed by Recyclable Copper(II) as well as Cobalt(II) Phthalocyanines

“…[22] A specific change in colour was also observed when hydrazine hydrate was added in the reaction mixture, supporting the involvement of Co(I)Pc in the reduction process. [19] The same observation was made when THF was used as solvent for UV analysis, where the red shift of the Q band from 670 to 714 nm was observed due to the transformation of Co(II)Pc to Co(I)Pc. Moreover, the steady decrease in the band at 714 nm and the appearance of the original band at 670 nm suggested the regeneration of Co(II)Pc.…”

“…[17] Recently, cobalt phthalocyanine has been used for the oxidation of thiols [18] and for the selective reduction of the double bond in flavones. [19] But to the best of our knowledge the catalytic potential of MPcs for selective reduction of the nitro group in the presence of other reducible functionalities has not been reported.…”

Cobalt(II) Phthalocyanine Catalyzed One‐Pot Synthesis of 2‐Substituted Benzimidazoles, Benzothiazoles and Benzoxazoles from Substituted Benzyl Alcohols

“…The UV‐Visible spectrum of Co II Pc ( 4 ) in DMSO showed a characteristic Q band at 658 nm . On addition of K t OBu to the above solution, Co II Pc got reduced to Co I Pc ( 5 ) and Q band was shifted to 704 nm and a new band at 466 nm corresponding to Co I Pc ( 5 ) was observed in the UV‐visible spectrum . This showed the involvement of Co I Pc in the current reaction system.…”

“…Co I Pc reacts with benzyl alcohol in the presence of molecular oxygen to generate the intermediate 6 and it gets oxidize to Co III Pc. Intermediate 6 contains Co III Pc which is confirmed by the presence of blue shifted characteristic Q band at 661 nm along with the disappearance of band at 466 nm in UV‐Visible spectrum ,. Intermediate 6 rearranges to give the benzaldehyde 7 which undergoes condensation reaction with o‐phenylenediamine to generate the intermediate 8 .…”

“…Recently our research group has successfully carried out metallophthalocyanines facilitated organic transformations such as oxidation, reduction and dechlorination of various organic moieties. [39][40][41][42][43] Metallophthalocyanines are structurally similar to metal porphyrins and are purely synthetic molecules, more stable to temperature and harsh reaction conditions than porphyrins, heterogeneous in nature and are insoluble in common organic solvents such as chloroform, DCM, ethyl acetate, alcohols, benzenes, etc. [44] Due to the insoluble nature, metallophthalocyanines are quickly used as heterogeneous catalysts.…”