ortho-Naphthoquinone-catalyzed aerobic oxidation of amines to fused pyrimidin-4(3H)-ones: a convergent synthetic route to bouchardatine and sildenafil

Efficient Access of Heterocycles Utilizing Inherent Carbodicationic Reactivity of Ynone via Lewis Acid Catalysed C─C Triple Bond Cleavage

Divalent carbodicationic synthon has attracted significant attention due to its unique reactivity and bonding. The application of this synthon in synthetic settings is still fancy owing to its super-electrophilicity. Generation of this reactive intermediate in a catalytic fashion is challenging. For the first time, the reactivity of the chemical equivalent of divalent dication synthon has been proposed via Lewis acid-catalysed heterolytic ionisation of ynone via sequential conjugate addition to ynone followed by C─C bond cleavage to afford heteroarenes. A library of quinazolinones and 2-substituted quinazolinones has been synthesised with good to excellent yields having a wide range of functional group tolerance and broad substrate scope using 2-amino benzamides as a nucleophilic partner. Furthermore, 1,2-diaminobenzenes afforded the corresponding benzimidazole in synthetically good yield. The generality of this strategy has been demonstrated by the successful synthesis of 6-mono and 2,6-di-substituted quinazolinones and 2,4,6-tri-substituted quinazoline with very high efficiency. The mechanistic study confirmed the role of the cooperative effect and secondary orbital interaction in Grob-type fragmentation and not the involvement of any radical intermediate in the catalytic cycle.

Visible-light-mediated photocatalytic aerobic oxidative synthesis of pyrazolo[4,3-d]pyrimidin-7(6H)-ones and sildenafil

A novel, efficient and sustainable methodology involving visible-light-mediated construction of pyrazolo[4,3-d]pyrimidin-7(6H)-ones from easily available 4-amino-1-methyl-3-propyl-1H-pyrazole-5-carboxamide and aldehydes in the presence of 4CzIPN under an oxygen atmosphere has been developed. This photocatalytic system worked under mild conditions and avoided the use of any excess amount of toxic oxidants and transition metals. A variety of functionalized products were obtained in good to excellent yields. Notably, the marketed drug sildenafil was successfully synthesized. In addition, a plausible reaction mechanism involving a radical process has been proposed and further applications of this protocol are under way in our laboratory.

Advances in structural identification of some thieno[2,3-d]pyrimidine scaffolds as antitumor molecules: Synthetic approaches and control programmed cancer cell death potential

Thieno[2,3-d]pyrimidine fragment is not only bioistostere to quinazoline ring but also to purines which exist in nucleic acids responsible for several key biological processes of the living cells, thus it is of a great interest for many researchers. Thieno[2,3-d]pyrimidine ring has become an important scaffold for different compounds with versatile pharmacological activities including anticancer. These compounds exert their anticancer activity through variant mechanisms of action; one of these is the induction of different programmed cell death types as apoptosis and necroptosis which is an effective approach for cancer treatment. This review highlights the different synthetic approaches of recent thieno[2,3-d]pyrimidine analogs along with their anticancer significance through induction of apoptotic or necroptotic cell death with illustration of the structure-activity relationship (SAR).

Bioinspired o-Naphthoquinone-Catalyzed Aerobic Oxidation of Alcohols to Aldehydes and Ketones

A biomimetic alcohol dehydrogenase (ADH)-like oxidation protocol was developed using an ortho-naphthoquinone catalyst in the presence of a catalytic amount of base. The developed organocatalytic aerobic oxidation protocol proceeds through the intramolecular 1,5-hydrogen atom transfer of naphthalene alkoxide intermediates, a mechanistically distinctive feature from the previous alcohol dehydrogenase mimics that require metals in the active form of catalysts. The ADH-like aerobic oxidation protocol should provide green alternatives to the existing stoichiometric and metal-catalyzed alcohol oxidation reactions.

One-Pot Direct Oxidation of Primary Amines to Carboxylic Acids through Tandem ortho-Naphthoquinone-Catalyzed and TBHP-Promoted Oxidation Sequence

Biomimetic oxidation of primary amines to carboxylic acids has been developed where the copper-containing amine oxidase (CuAO)-like o-NQ-catalyzed aerobic oxidation was combined with the aldehyde dehydrogenase (ALDH)-like TBHP-mediated imine oxidation protocol. Notably, the current tandem oxidation strategy provides a new mechanistic insight into the imine intermediate and the seemingly simple TBHP-mediated oxidation pathways of imines. The developed metal-free amine oxidation protocol allows the use of molecular oxygen and TBHP, safe forms of oxidant that may appeal to the industrial application.

Aerobic primary and secondary amine oxidation cascade by a copper amine oxidase inspired catalyst

A CAO inspired catalyst catalyzed the cascade aerobic oxidation of primary and secondary amines for the synthesis of quinazolin-4(3H)-one core in high yields. Like the natural CAOs, a copper ion improves the o-quinone cofactor's catalytic activity.