In the present work, a series of 1-benzyl-2-alkylbenzenes functionalized was subjected to intramolecular cyclization reaction promoted by iron(III) chloride with diorganyl dichalcogenide allowed the synthesis of 9-(organochalcogen)-5H-benzo[7]annulenes whereas the mutual action between diorganyl dichalcogenide and iron(III) chloride in a 0.5:1.0 mole ratio was essential in order to achieve the maximal yields of the products. The cyclization reaction tolerated a variety of functional groups, such as trifluoromethyl, chloro, fluorine and methoxyl, in both 1-benzyl-2-alkynylbenzenes and diorganyl diselenides, giving the seven-membered carbocyclic exclusively via a 7-endo-dig cyclization process, it resulted in a total of 23 samples in 45-77 % yield. / No presente trabalho, uma série de 1-benzil-2-alquilbenzenos funcionalizados foi submetida à reação de ciclização intramolecular promovida por FeCl3 com dicalcogeneto de diorganoíla, permitindo a síntese de 9-(organocalcogênio)-5H-benzo[7]anulenos. Considerou-se que uma ação mútua entre o dicalcogeneto de diorganoíla e o cloreto de ferro (III), de proporções molares 0,5:1,0, é essencial para os produtos atingirem bons rendimentos. A reação de ciclização tolera uma variedade de grupos funcionais tais como trifluormetil, cloro, flúor e metoxila , em ambos os 1-benzil-2-alquilbenzenos e dicalcogeneto de diorganoíla, levando aos carbociclos de sete membros, exclusivamente por meio de um processo de ciclização 7-endo-dig, resultou-se em um total de 23 exemplos com 45 - 77% de rendimento.

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)