Thio metallates are known for many years for their utility in many processes. They have been established as versatile reagents in organic synthesis. However the heavier metal chalcogenides, though known for many years, have been ignored for a long time. In this thesis the results of the development of tetraethylammonium tetraselenotungstate [EttN]2Wse4 1 as a new class of selenium transfer reagent have been described. The thesis also deals with the chemistry of benzyltriethylammonium tetrathiomolybdate, [BnEt3N]2MoS4,2 in the synthesis of diselenides and thio esters. The thesis entitled "Chemistry of Thio and Seleno Metallates in Organic Synthesis" is divided into four Chapters. Chapter 1 In this chapter a detailed studies of alkylation of tetraethylammonium tetraselenotungstate (EuN)2WSe4,1 with a variety of alkyl halides, benzylic halides and acyl halides to yield the corresponding diselenides in excellent yields are described. (structural Formula) Scheme 1 Various carbohydrate-derived diselenides were also prepared by treating the sugar bromides with tetraethylammonium tetraselenotungstate 1 (Scheme 2). An attempt was made to synthesize seleno lactones from co- bromo acyl halides. This reaction mainly furnished the corresponding diacyl diselenides (Scheme 3). The reaction of 1 with aryldiazonium tetrafluoroborates led to the formation of corresponding diselenides or mono selenides depending on the substitution on the aromatic ring (Scheme 4). (structural formula) Scheme 2 (structural formula) Scheme 3 (structural formula) Scheme 4 Chapter 2 In this chapter a general methodology for the formation of the diselenide bond has been extended to the synthesis of a number of redox- switched crown ethers of various ring size using the reagents tetraethylammonium tetraselenotungstate (Et4N)2WSe4 t 1 and benzyltriethylammonium tetrathiomolybdate, [BnEt3NJ2MoS4,2 (Scheme 5). (structural formula) Scheme 5 The association constants for the binding of silver and potassium ions with the diselena crown ethers were determined. This methodology is very useful for obtaining selenacrown ethers under very mild conditions and also without using high dilution conditions. Chapter 3 In this chapter a general methodology for the facile conversion of amides and lactams to the corresponding seleno amides and selenolactams is described. A number of amides and lactams were converted into their selenocarbonyl derivatives in excellent yield via the formation of Vilsmeier intermediates followed by treatment with tetraethylammonium tetraselenotungstate (EuN^WSe4,1 (Scheme .6). (structural formula( Scheme 6 Chapter 4 In this chapter, a general method for the synthesis of thioesters is described. The reaction of p- nitrophenyl esters and disulfides with benzyltriethylammonium tetrathiomolybdate (PhCH2NEt3)2MoS4,2 furnished the corresponding thio esters in good yield (Scheme (7). The intramolecular version of this reaction furnished dimeric thiolactones as the major product (Scheme 8) (structural formula) Scheme 7 (structural formula) Scheme 8 (for structural formula pl see the original document)

The thesis entitled “Chemistry of Tetrathiomolybdate and Tetraselenotungstate: Studies on Aziridine and Epoxide Ring Opening Reactions” is divided into five chapters. (For Formulas and Equations Refer PDF File) Chapter 1: Part 1: Synthesis of β-Sulfonamidodisulfides and β-Sulfonamidosulfides using Benzyltriethylammonium Tetrathiomolybdate In this chapter, a comprehensive study of general and effective one step procedure for the synthesis of β-sulfonamidodisulfides directly from optically pure N-tosyl aziridines using benzyltriethylammonium tetrathiomolybdate [BnEt3N]2MoS4 as sulfur transfer reagent in a regio manner under neutral conditions without the use of any Lewis acid or base has been reported. Additionally, we have demonstrated regio- and stereospecific ring opening of di- and trisubstituted aziridines using [BnEt3N]2MoS4 to synthesize substituted β-sulfonamidodisulfides in good yields. This methodology is extended to the synthesis of an optically pure unnatural amino acid with the disulfide bridge and a cyclic seven membered disulfide. Synthesis of a variety of β-sulfonamidosulfides involving cleavage of disulfide bonds assisted by tetrathiomolybdate and the use of masked thiolate for the synthesis of β-sulfonamidosulfides involving multi-step reactions in a one pot is also demonstrated. Chapter 1: Part 2: Synthesis of β-Sulfonamidodiselenides using Tetraethylammonium Tetraselenotungstate In this chapter, we report the results of regio- and stereospecific, nucleophilic ring opening of chirally pure N-tosyl aziridines with tetraethylammonium tetraselenotungstate [Et4N]2WSe4 as selenium transfer reagent to afford a number of β- sulfonamidodiselenides in good yields. Using this methodology, carbohydrate derived β- sulfonamidodiselenides from the corresponding carbohydrate derived aziridines have been synthesized. These enantiopure diselenide derivatives have the potential to be used as chiral ligands in diethyl zinc addition to aldehydes. Chapter 2: Ring Opening of Aziridine/Epoxide, Disulfide Formation, Reduction of Disulfide Bond and Michael Reaction In this chapter, we report a systematic study of tetrathiomolybdate mediated tandem regio- and stereospecific ring opening of aziridines, disulfide formation, in situ reduction of disulfide bond followed by Michael reaction in an one pot operation to give a variety of β-sulfonamidosulfides in good yields. The main advantage of this methodology is that four reactions involving three components take place in a one-pot operation. Chapter 3: Part 1: New Thia-aza Payne type Rearrangement Mediated by Benzyltriethylammonium Tetrathiomolybdate In this chapter, reaction of aziridinemethanol sulfonate esters with tetrathiomolybdate to give thiirane derivatives as the major product and cyclic disulfides as minor product under mild reaction conditions via an unprecedented thia-aza-Payne type rearrangement have been presented. Interestingly, when the reaction of tetrathiomolybdate was carried out with 2-aziridino-cyclohexanol derivatives it resulted in the formation of thia-bicyclo[3.1.1]heptane or dithia-bicyclo[3.2.1]octane derivatives. Chapter 3: Part 2: New selena-aza Payne Type Rearrangement Mediated by Tetraethylammonium Tetraselenotungstate In this chapter, reaction of tetraselenotungstate with simple N-tosyl aziridinemethanol tosylates to give allyl amine derivatives as the only product via an unprecedented selena-aza-Payne type rearrangement is discussed. When the methodology is extended to disubstituted N-tosyl aziridinemethanol tosylates, regio- and stereospecific ring opening of aziridines occurs to afford allyl amine derivatives as the major products and cyclic five membered diselenides as the minor products in good yields. Chapter 3: Part 3: Synthesis of Sulfur and Selenium Heterocycles by Azirdine Ring Opening followed by Cyclization In this chapter, studies on the synthesis of sulfur and selenium-heterocycles by aziridine ring opening followed by cyclization of N-tosyl aziridino-ethanol tosylates using tetrathiomolybdate as a sulfur transfer reagent and tetraselenotungstate as a selenium transfer reagent respectively are presented. Chapter 4: Tetrathiomolybdate Mediated Ring Opening of bis-Aziridines, bis-Epoxides and Aziridino-epoxides In this chapter, studies on the synthesis and ring opening of bis-aziridines, bis-epoxides and aziridino-epoxides with tetrathiomolybdate as the sulfur transfer reagent are presented. This has resulted in the synthesis of optically active sulfur heterocycles ranging from three membered to eight membered ring systems with excellent stereo and regio- control in good yields. Chapter 5: Part 1: Synthesis of Conformationally Locked, Bridged, Bicyclic Mono and Disulfides In this chapter, work related to the synthesis of conformationally locked bridged bicyclic disulfides and sulfides from cis-aziridino-epoxides by ring opening of both aziridines and epoxides in a tandem fashion using tetrathiomolybdate as a sulfur transfer reagent has been discussed. Comparative studies on the behavior of conformationally locked disulfides which has the dihedral angle close to zero (φ = 0) with disulfides having larger dihedral angles (φ>90) have been presented in this chapter. Some correlations have been made on the physicochemical characteristics of the disulfides with change in the dihedral angles. Chapter 5: Part 2: Synthesis of Conformationally Locked, Bridged, Bicyclic Diselenides In this chapter, work related to the development of a general synthetic methodology for the synthesis of conformationally locked, bridged diselena-bicyclo[3.2.1]octane skeleton by regio- and stereospecific, tandem nucleophilic ring opening of cis-1,4-aziridino-epoxides with tetraselenotungstate in one-pot are presented. To compare the behavior of conformationally locked diselenides which has the dihedral angle close to zero (φ = 0) with diselenides having larger dihedral angles (φ > 90), we have synthesized the acyclic diselenide (see chapter 1.2) and cyclic diselenide by regio- and stereospecific ring opening of simple aziridine and bis-aziridine respectively with tetraselenotungstate. Some correlations have been made on the physicochemical characteristics of the diselenides with change in the dihedral angles.