Search

A convenient and regioselective synthesis of 1,3-dithiolanes from terminal alkynes under photoredox conditions.

A DMAP-catalyzed, highly diastereoselective, [3+2] cycloaddition of pyrazolone-derived Morita–Baylis–Hillman carbonates to 3-methyleneoxindoles has been developed. A variety of structurally diverse and complex spiropyrazolone-fused oxindoles bearing three contiguous chiral centers have been synthesized in high yields (up to 98%) and with excellent diastereoselectivities (up to 99:1). Moreover, the synthetic potential of this protocol has been demonstrated by performing a Suzuki coupling reaction.

The cyanation of organic compounds is an important and useful process as it directly provides nitriles which in turn can be utilized for different transformations. Although, thiocyanate salt has emerged as a very mild and environmentally friendly “source of CN” alternative to toxic and metal based cyanating reagents; its synthetic utility for the cyanation is highly limited to very few types of organic compounds. We have explored the reactivity of sodium thiocyanate for directly cyanating cyclic thioacetals for accessing thiocayano-thioesters with two different functional groups in one pot using photoredox catalysis under mild reaction conditions. Based on the reactivity of thiocyanate radical, the protocol has been further extended for the direct cyanation of disulfides and diselenides to access aryl thiocyanates and aryl selenocyanate. A series of control experiments and Stern-Volmer studies have been carried out to validate the mechanistic pathways.

Herein we report the efficient synthesis of α-acyloxycarbonyl compounds and esters starting directly from aldehydes and α-bromocarbonyl compounds/benzyl bromide derivatives and bromo nitriles using an organic photocatalyst in combination with silver tetrafluoroborate under visible light at room temperature. The reaction is compatible with a variety of functional groups and has been successfully applied to the synthesis of various molecules. The strength of this protocol was effectively demonstrated by utilising both aromatic and aliphatic aldehydes. The detailed controlled studies including the labeling experiment and fluorescence spectroscopic data clearly revealed the reductive quenching of the photoredox catalytic cycle.

A highly regioselective [3 + 2] annulation of Morita-Baylis-Hillman (MBH) carbonates of isatin with aurone/thioaurone is developed. Spiroheterocycles such as spirooxindole cyclopentadiene and spirooxindole fused hydroxy cyclopentene derivatives are constructed in one pot by exploring the reactivity of Lewis bases. Combined experimental and density functional theory (DFT) calculations offered an insight into the reaction mechanism.

An efficient and straightforward method has been developed for the synthesis of β-benzyl-substituted five-membered heterocyclic carbaldehydes via transient directing group-enabled direct γ-C(sp3)−H...

A tertiary amine catalyzed highly diastereoselective and enantioselective [3 + 2] annulation between Morita-Baylis-Hillman (MBH) carbonates derived from isatin and pyrazolone 4,5-diones has been developed. A series of structurally diverse and multifunctional spirooxindole dihydrofuran fused pyrazolone derivatives with two adjacent quaternary spirocenters has been achieved in excellent yields with good to excellent enantioselectivity. Further synthetic utility of this protocol has been successfully demonstrated by employing the bromo derivative of spirooxindole dihydrofuran fused pyrazolone to Suzuki coupling.

Visible light promoted chemo-selective metal free hydrogenation of activated double bond has been achieved via photoredox catalysis. Eosin Y has proved to an efficient catalyst for the effective reduction of C-C double bonds of isatins, oxindoles and maleimides under visible light. The method worked efficiently without the aid of any external reductants. Commercially viable DIPEA has been employed as a sacrificial electron donor and it’s in-situ generated cationic radical acts as reductant in this transformation. The method proved to be practical as a broad range of substrates containing activated double bond were easily reduced. The method proved to be scalable on a gram scale and the reduced product has been utilized successfully for the further synthetic application. The systematic and detailed mechanistic studies reveal the reductive quenching of the photocatalyst by the activated double bond.

Base dependent oxidative rearrangement of dithiolanes and dithianes to access disulfide-linked-dithioesters under visible-light photoredox catalytic conditions has been disclosed. The protocol demonstrated the ability to synthesize either rearranged product or sulfoxide by simply switching the base with inherent ability to make hydrogen bonding with sulfur atom. Unlike, the usual deprotection of thioacetals to corresponding aldehydes under the oxidative conditions, we observed the unique regioselective oxidative reactivity of thioacetals to form disulfide-linked-dithioester or sulfoxides. The generality of the protocol has been demonstrated by exploring a wide range of substrates. As an application the in-situ generated thyil radical has been trapped with disulfides to prepare hetro-disulfides of potential utility. The protocol proved to be practical on gram scale quantity and relied on clean energy source for the transformation. Based on the series of control experiments, cyclic volametry and Stern-Volmer studies the plausible mechanism has been proposed.

A silver triflimide catalyzed one-pot protocol for the diastereoselective synthesis of dihydrobenzoxepines has been developed. Silver triflimide found to be an efficient catalyst for the formal (5+2)-cycloaddition to access dihydrobenzoxepines as a single diastereomer using vinyl diazo compounds as 5-C-synthons and ketones. An unmet challenge of utilizing the donor-/acceptor-type vinyl diazosuccinimides as 5-C-synthons under silver-catalysis is presented. This protocol found to be highly regio-, chemo- and diastereoselective, and works well with aliphatic as well as aromatic methyl ketones bearing electron deactivating as well as donating groups to afford dihydrobenzo[5,6]oxepino[2,3-c]pyrroles with a broad substrates scope. The control experiments and time dependent NMR studies revealed the plausible mechanism of this transformation. The protocol also proved to be scalable on the gram scale synthesis.