Tiziano Nocentini

2-Trimethylsilyl-1,3-dithiolane as a masked dithiolane anion

Abstract 2-Trimethylsilyl-1,3-dithiolane, easily obtainable through transthioacetalization of corresponding silylated acetals, can be efficiently reacted, under fluoride-ion catalysis, with different organic electrophiles, leading to a general and mild functionalization protocol. This reactivity discloses the ability of compound 3 to act as a masked dithiolane anion.

An easy access to α,β-unsaturated thioacylsilanes: a useful route to silylated 1,2-dithiins

Abstract Treatment of different silylated allenes with hexamethyldisilathiane (HMDST) in the presence of CoCl2·6H2O affords an easy and high yielding access to α,β-unsaturated thioacylsilanes, which undergo a self-dimerization reaction to afford polyfunctionalized 1,2-dithiins as the major products.

Acetylenic silyl ketone as polysynthetic equivalent of useful building blocks in organic synthesis

Abstract Ethynyl silyl ketone 1 proved to be a very efficient Michael acceptor in carbocupration and metallocupration reactions. In particular, when using carbocuprates, a smooth entry to polyenals can be obtained, while, when using metallocuprates, silyl- and stannylpropenoyl silanes may be obtained, very powerful intermediates in organic synthesis.

Organothiosilanes in the synthesis of functionalized benzothiophenes and benzofurans

Fluoride-ion-induced reactivity of bromo(phenylthio)methyltrimethylsilane with o-hydroxy benzaldehyde and o-mercaptobenzyl alcohol afforded direct and simple access to 2,3-dihydro-2-phenylthio-3-hydroxybenzofuran and 2-phenylthio-3-hydroxy-2,3-dihydrobenzothiophene, respectively. 2-Phenoxy-3-hydroxy-2,3-dihydrobenzo-thiophene could be similarly obtained through a slightly modified procedure.

HMDST as Useful Tool in Organic Synthesis: A Further Step in the Delivery of Sulfur Functionalities

Abstract Bis(trimethylsilyl)sulfide (HMDST) was demostrated to be a very efficient reagent in the delivery of sulfur functionalities, allowing us to synthesize a wide range of thiocarbonyl compounds. The most reactive derivatives were trapped with suitable dienes, leading to the synthesis of different heterocyclic molecules with an high degree of chemo- and regioselectivity. Recently, the mildness of this methodology also allowed us to obtain particularly reactive thiooxocompounds, such as thioformylsilanes, α,β-unsaturated thioaldehydes, thioketones, thioacylsilanes, and thioacylstannanes.

A General Access to 2-Silylthiazolidines and Their Reactions Under Fluoride Ion Conditions

Trimethylsilylthiazolidines were readily obtained through reaction of aminoethanethiol with (bromomethoxymethyl)trimethylsilane and efficiently N-functionalized with a variety of protecting groups. Such N-protected thiazolidines can then be satisfactorily reacted with several organic electrophiles under fluoride ion conditions, with a clean transfer of the thiazolidine moiety, to afford good yields of 2- functionalized heterocycles. The thiazolidine ring system derives special importance from the fact that it is an integral part of medicinally important compounds like the penicillins (1) and some antiradiation drugs (2). Substituted thiazolidine derivatives represent important key intermediates for the synthesis of pharmacologically active drugs (3). Recently a number of thiazolidines have been claimed to be retroviral protease inhibitors (3b,4) and have also been investigated as possible substitute for the carbohydrate moiety in the synthesis of new antiviral nucleosides (5). More recently they have also been shown as antitussive active molecules (6). Thiazolidines are also relevant in food chemistry, as far as they are incorporated in flavor enhancing additives (7), and their synthetic utility is shown by their use as blocking groups (8), and as intermediates in the synthesis of aldehydes (9) and aminoethane thiols (10). Despite the utility of the thiazolidine moiety, still very few methodologies for the functionalization of position 2 of the heterocyclic ring exist. Only two reports, in fact, to the

α,β-Unsaturated thioacylsilanes as efficient dienes in hetero Diels–Alder reactions

Abstract Reaction of several α,β-unsaturated thioacylsilanes with in situ generated thioaldehydes and thioacylsilanes affords under mild conditions a clean and regioselective access to 2-substituted 4-silyl-1,3-dithiacyclohex-4-ene derivatives, arising from an hetero-Diels–Alder reaction between two different thiocarbonyl compounds.

Synthesis and Reactivity of New Silylated Sulfur-Containing Heterocyles Through Thionation of Bis(Acylsilanes)

Abstract The optimization of the synthesis of 2,6-bis(trialkylsilyl)4H-thiopyranes and some aspects of the reactivity of the corresponding lithium salts with alkyl halides and benzaldehyde are presented.

Synthesis and Stereoselective Functionalization of Sulfur-Containing Silyl Heterocycles

Abstract 2-Silylated five-membered heterocycles can be easily accessed through reaction of bromo(methoxy)methylsilane and dithiols, mercapto amines, and mercapto alcohols. Further reaction of the obtained silylated heterocycles with electrophiles under fluoride ion conditions afford an easy functionalization of such molecules.

Synthesis, metallation and nucleophilic reactivity of 2,6-bis(trialkylsilyl)-4H-thiopyrans

We report herein (i) the synthesis of 2,6-bis(trialkylsilyl)-4H-thiopyrans by thionation-cylisation of 1,5-bis(acylsilanes) and (ii) the lithiation of these thiopyrans and reaction of their lithium salt with various electrophiles. Most reaction led to alkylation at carbons in position 4 and 2, the former being generally more regioselective. Partial reaction at sulfur atom occurred in case of n-hexyl bromide. An effective and totally regioselective trimethylsilylation led to a 2,4,6-tris(trialkylsilyl)-4H-thiopyran. Its lithium salt exhibited also interesting properties: Peterson olefination products were formed under reaction with aldehyde, and a stable thiabenzene was effectively obtained with n-hexylbromide. The role of the silyl substituents was decisive to explain the particular aspects of the reactivity of these silyl substituted thiopyrans. GRAPHICAL ABSTRACT