G. Maccagnani

Chiral silicon in asymmetric synthesis. Addition of organometallic reagents to a silyl thione chiral at silicon

Abstract The reaction of R-(-)-methyl-α-naphtyl-phenylsilyl phenyl thioketone 1 with organolithium derivatives and Grignard reagents gives the α-silylsulphides 3 with medium to good levels of asymmetric induction. The asymmetry induced at the α-carbon is retained in the subsequent desilylation.

[4+2]-cycloadditions of thiones with nitrosoalkenes: synthesis of derivatives of 4H-1,5,2-oxathiazine, a new heterocyclic system.

Abstract Conjugated nitrosoalkenes, generated in situ via dehydrobromination of α-bromoketoximes, undergo an easy [4+2]-cycloaddition with thiocarbonyl compounds to give very high yields of the new heterocycles 4H-1,5,2-oxathiazines. The thermolysis and the behaviour to oxidation of these adducts were tested.

Asymmetric induction by chiral silicon. Synthesis and electrophilic reactivity towards dienes and carbanions of R-(–)-methyl-α-naphthyl-phenylsilyl phenyl thioketone

The title compound was prepared by acid catalysed reaction of the corresponding ketone with hydrogen sulphide, and its ability to transfer chirality to the carbon α to silicon in reactions with buta-1,3-diene and methyl-lithium was tested; good levels of asymmetric induction were observed.

Synthesis and chemical behaviour of thioacylsilanes (silyl thioketones). Part 1. Oxidation to S-oxides, conversion into silylated thiiranes, silylated triarylethylenes, and α-silylated sulphides

Trimethylsilyl and triphenylsilylaryl thioketones have been synthesized by acid catalysed reaction of the corresponding ketones with hydrogen sulphide. Such silylated thioketones have been oxidized to give S-oxides and converted with diaryldiazomethanes into triaryl thiiranes; upon treatment with organolithium nucleophiles they undergo thiophilic addition. The ready desulphurization with triphenylphosphine of silylated thiirans to the corresponding silyl triaryl ethylenes is also reported.

Chemistry of silyl thioketones. Part 5. Synthesis and properties of alkyl α-silyl thioketones: a comparison with aryl derivatives

t-Butyl and methyl trimethylsilyl thioketones have been synthesized, and the reactivity towards organometallic compounds, dienes, and oxidation, and the desilylation of the resulting adducts, have been investigated. Where possible, a comparison with aryl trimethylsilyl thioketones has been made.

Deoxygenation of Pyridine N-oxides with sulphur monoxide generated from trans-2,3-diphenylthiiran-1-oxide

Abstract Pyridine N-oxides are deoxygenated by sulphur monoxide. Electron withdrawing substituents lower drastically the yields of reduction.

Silyl thioketones and silylated thiirans

The preparation of silyl thioketones, and their reactions leading to silylated thiirans and other hitherto unknown silylated heterocycles, are reported.

Sulphines. Part VIII. Kinetics and mechanism of the reaction between aryl sulphines and perbenzoic acid

Aryl sulphines are converted by perbenzoic acid into benzophenones, sulphur, and sulphur dioxide. The reaction shows kinetic features, namely the rate law as well as substituent and solvent effects, similar to those reported for the oxidation of thiones, sulphides, alkenes, acetylenes, and diazoalkanes with the same peroxyacid. The reaction is an example of oxidation of a cumulative, double-bond system and a multi-step reaction mechanism is advanced. The rate-limiting step is electrophilic attack of the peracid on the carbon–sulphur double bond of the CSO group to form a cyclic sulphinic ester; this intermediate, by rapid cleavage, gives the ketone and sulphur monoxide, the latter disproportionating into sulphur and sulphur dioxide. The reaction rates of the E- and Z-isomers of mesityl phenyl sulphine compared with that for diphenyl sulphine, give further evidence for the proposed mechanism.

Chemistry of silyl thioketones. Part 4. 2,4,6-Triaryl-2,4,6-tris(trimethylsilyl)-1,3,5-trithianes from silyl thioketones: crystal structure of 2,4,6-triphenyl-2,4,6-tris(trimethylsilyl)-1,3,5-trithiane and stereochemistry of desilylation with fluoride ion

Silyl thioketones are easily converted into the corresponding trimers (1,3,5-trithianes) under acidic conditions. Both the α-(cis,trans)- and the β-(cis,cis)-isomers were isolated. The β-diastereoisomers predominate over the α-form. The major isomer from the trimerisation of trimethylsilylphenyl thioketone, upon X-ray analysis, shows a chair-like conformation with the silyl groups all equatorial. Desilylation of the α- and β-trimers of the trimethylsilylphenyl thioketone with fluoride ion affords, stereospecifically, the two isomeric 2,4,6-triphenyl-1,3,5-trithianes.

Formation of 3,6-dihydro-1,2,4-oxathiazines from thioketone S-oxides and a 2H-azirine via a new type of [3,3] cycloaddition reaction

Diarylthioketone S-oxides react with the 2H-azirine (1) in the presence of boron trifluoride–diethyl ether to give the oxathiazines (3)via a 1,3-cyclization across the sulphine C–S–O bond; the oxathiazines (3) rearrange thermally to the sulphoxides (5).