Current Organocatalysis (v.1, #1)

Preface by Bimal K. Banik (1-1).

The Wieland-Miescher ketone 4 serves as starting material for a wide range of natural product synthesis.Thisprocedure represents one of the most efficient method for the synthesis of Wieland - Miescher ketone 4 with 1 mol% catalystloading. PEG (400) mediated proline was used as catalyst to achieve the Wieland - Miescher ketone 4 via a nonselectiveconjugated addition reaction tailed by an enantioselective intermolecular Aldol condensation reaction of triketone3 intermediate. All the reaction products were well characterized by sophisticated analytical techniques such asNMR, FTIR, HPLC, HRMS etc. Short reaction time, 8 times recycling of the catalyst, good yield (90%) and selectivity(99% ee) are the major outcomes of this proposed protocol.

Imidazol-1-yl-acetic acid is introduced as a new, efficient and recyclable green bifunctional organocatalyst forthe synthesis of β-hydroxythiocyanate and 1,2-azido alcohols under mild conditions. This catalyst can be recovered bysimple filtration and recycled up to 8 consecutive runs without losing any of its efficiency. Various advantages associatedwith this protocol include simple workup procedure, short reaction times, high product yields, greater regioselectivity.

N-Heterocyclic Carbenes (NHCs) in Asymmetric Organocatalysis by Seema Dwivedi, Sumanta Gupta, Sajal Das (13-39).
Asymmetric synthesis is a crucial and valuable branch of synthetic chemistry. Organocatalytic methods of synthesisare known for their greener approach towards scientific developments. These involve simple molecules as catalyststhat are less sensitive and can be easily and effectively employed in various systems with simple reaction conditions. Inthe recent past organocatalytic asymmetric syntheses have thus grasped the attentions of chemists worldwide. Remarkablecontributions of N-heterocyclic carbenes have proved them to be valuable addition in this arena affording new possibilitiesand enabling a range of unique synthetic transformations that are otherwise inaccessible. High enantioselectivity levelshave been achieved in many cases including umpolung reactions such as benzoin condensation, Stetter reaction, reactionsinvolving enolates and homoenolates, etc. This review summarizes the recent developments in the reactions that canbe carried out with NHC organocatalysts.

Poly(4-vinylpyridine) (P4VP) has been found as an efficient recyclable heterogeneous Lewis base catalyst forthe diastereoselective synthesis of syn-2-nitroalkanols in aqueous medium. The 1H NMR and 13C NMR spectra of 2-nitroalkanols are utilized for determining the ratios of syn/anti stereoisomers. This protocol provides a simple greener pathfor the synthesis of 2-nitroalcohols in aqueous medium at ambient condition with high yields.

Sucrose as an Environmental and Economical Catalyst for the Synthesis of 2(5H) Furanone by Nourallah Hazeri, Malek Taher Maghsoodlou, Nasrin Mahmoudabadi, Razieh Doostmohammadi, Sajjad Salahi (45-50).
A simple and convenient one-pot multi-component reaction has been described for the synthesis of 3,4,5-substituted furan-2(5H)one from amines, aldehydes and dialkyl acetylenedicarboxylates in presence of sucrose. Thismethod offers several advantages such as high yield, using sucrose as a cheap and readily available catalyst, readily availablestarting materials, and involving less hazardous chemical techniques.

Structurally diverse unsymmetrically annulated 1,4-dihydropyridines have been synthesized by L-proline catalyzedfour-component domino protocol involving the reaction of 2-aminobenzothiazole, thiophene-2-carbaldehyde andcarbonyl compounds in ethanol. The utilization of L-proline in the multicomponent reaction will make the present protocolattractive for synthesis of 1,4-dihydropyridines in terms of reaction efficiency, atom-economy and environmentalsafety.

A straightforward green synthesis of 2,3-dihydropyrazines was accomplished under the catalytic influence of(±)-Camphor-10-sulfonic acid at room temperature by condensation of aliphatic 1,2-diamines with α,β-dicarbonyl compoundsin aqueous medium. Remarkable aspects of this newly reported method are high yields, use of non-toxic solvents,mild conditions, simple workup and synthesis of complex molecules using an ecofriendly inexpensive organocatalyst. Thepresent method is atom-economical, environmentally benign, and affords synthetically useful and challenging productsvery rapidly.

A green and highly efficient method for the synthesis of 1,8-dioxooctahydroxanthenes catalyzed by melaminetrisulfonic acid (MTSA) as a heterogenous and recyclable organocatalyst under solvent-free conditions is reported. Thisprocedure provides many advantages such as easy work-up, clean conversions, short reaction times and high yields of theproducts.