Heterocycles oxathianes

When a mixture of p-anisaldehyde and dimethyl sulfone was treated with excess potassium t-butoxide in DMF at 60-65 °C, bis-unsaturated sulfone 277 was obtained. In the reaction at 50 °C using a small amount of base, the main product was a heterocyclic compound, i.e., 2,4-di-p-methoxyphenyl-l,4-oxathiane 4,4-dioxide 278358. 

Considering the formation of saturated five-membered heterocycles with two heteroatoms, it is worth to note the possibility to prepare 1,3-dioxolanes, dithiane, oxathianes 148 [93] and dioxolanones 149 [94] by condensation of the corresponding carbonyl compounds under microwave irradiation in acid medium (Scheme 52). The reaction, which is very useful for the protection of carbonyl compounds or for the preparation of useful synthetic intermediates, has also been carried out under batch conditions over Montmorillonite KIO clay in more than 150 g scale, using a 1 L quartz reactor [95]. 

Another type of heterocycle containing two heteroatoms susceptible of being cleaved reductively are 1,3-dioxanes or 1,3-oxathianes 422. They were treated with lithium and a catalytic amount of DTBB (4.5%) in THF at room temperature (Y = O) or at —78 °C (Y = S) to yield, after hydrolysis with water, functionalized homobenzylic alcohols 425 (Scheme 119) . The participation of intermediates 423 and 424 has been postulated in order to explain the obtained results. 

The solid-state structure of one benzo derivative of 1,3-oxathiane 96 has been studied the heterocyclic moiety was found to adopt a half-chair conformation with the aryl substituent in an equatorial position <1998JFA4002>. 

A [4-f2] cycloaddition was the key step in the synthesis of substituted dihydrothiopyrans from 2-alkenyl-l,3-oxathianes and an alkene. The reaction was mediated by a Lewis acid. It is assumed that the Lewis acid attacks the oxygen of the heterocycle which upon ring opening gives the highly reactive cationic heterodiene which reacts with alkenes to the thiopyrans in 31-88% yield (Scheme 75) <2000TL371>. 

Thietes, four-membered precursors for the synthesis of 1,3-dilhianes or 1,3-oxathianes, provide access to the target heterocycles by reacting with either carbon disulfide and Lil <2002IJB1234, 2003S340> or, when the ring system denoted in Scheme 110 is aromatic, with diethyl 2-oxomalonate via a [4-1-2] cycloaddition pathway <1998JHC1505>. 

Six-membered non-aromatic heterocycles containing more than one heteroatom Morpholines, 1,4-dioxanes, 1,4-oxathianes Six-membered aromatic heterocycles containing one heteroatom Pyridine... 

The impact of commercial yeast strains on wine fermentation leads to the formation of metabolites of yellow passion fruit (Passiflora edulis Sims) 2-methyl-4-propyl-l,3-oxathian 79 (10MI282,98JAFC1076,98MI53). This oxathian exists in four enantiomeric forms, 79a-d, and there are pronounced sensory differences between them (06CRV4099) for their enan-tioselective synthesis, cf. (84HCA947, 85LA1185). It should be mentioned that most of the aforementioned sulfur heterocycles are sold worldwide as fragrances and flavors. 

The optically active 1,3-oxathiane derivative 81, synthesized as a chiral auxiliary (cf. Scheme 30), has been reported. The isomers were assignend by X-ray diffraction in the solid state trans) and by NOE experiments in solution cis) (97CPB778). Rules for the specification of the absolute configuration of the enantiomers R or S) for 1,3-oxathianes and other heterocycles with at least two hetero atoms were proposed and proved... 

In the same extract (SP II) we found another new compound in wine flavor, 2-methyl-l,3-oxathiane (10). The formation of this heterocyclic sulfur compound with chemical, burnt odor properties can be explained as a mixed acetal of 3-mercaptopropanol with acetaldehyde. 3-Mercaptopropanol, however, is not known as... 

Many new tertiary phosphines have been prepared by synthetic elaboration of simpler organophosphines which does not involve the phosphorus atom. Chiral phosphines bearing heterocyclic substituents have been obtained by elaboration of arylphosphines bearing amino, carboxaldehyde or nitrile groups, respectively, giving, e.g. the pyrrolidinyl system (147), phosphino-oxazolidines, e.g. (148), phosphino-oxathianes, e.g. (149), phos-phino-oxazines (150), and the phosphino-oxazolines (151). Wittig reac-... 

The reduction of 2-acyl- 1,3-oxathianes such as 3.96 (X = S) or of 2-acyl-3-oxa-N-benzylpiperidines 3.96 (X = NCH2Ph) can also take place with or without chelation control [El, EFl, EH2, KEl, KF4]. In cases of chelation control, the oxygen atom of the heterocycle participates in the chelation process (Figure 3.32). When the reaction is carried out with Li(5-Bu)3BH in the presence of Lil as an additive, the reduction occurs under chelation control. However, when using two equivalents of DIBAH, each of them coordinates to a one basic site, and no chelation takes place. The use of these chiral auxiliaries allows the synthesis of nonracemic a-hydroxyaldehydes or a-hydroxyesters with a high enantiomeric excess [NNl, S3]. 

X-ray diffraction studies have suggested that the anomeric effect operates in 2-phosphinoyl derivatives of the saturated heterocycles, where the 2-substituent has no lone electron pairs. For example, in 2-diphenylphosphinoyl-l,3-dithiane, the substituent occupies an axial position, in contrast to the 1,3-dioxane and 1,3-oxathiane derivatives, where the same substituent occupies an equatorial position <84JOC3026,88JOC3609,88TL6801>. 

Most of the chemistry associated with this series of heterocycles is a consequence of the acetal moiety. For example, all three saturated systems undergo acetal hydrolysis, the dioxanes being the most acid-sensitive. The chemistry of 1,3-dithianes and 1,3-oxathianes is further dominated by the acidity of the C-2 protons, leading to the use of the derived carbanions as acyl anion equivalents, particularly in the case of 1,3-dithiane derivatives. Oxidation at sulfur is also a common process. 

The commonly encountered C-2 anions derived from 1,3-dithiane and 1,3-oxathiane and their derivatives can be generated by treatment with any of a wide range of bases, but typically n-butyllithium (for 1,3-dithianes) or yec-butyllithium (sometimes necessary for 1,3-oxathianes). There are many instances where the deprotonated heterocycles have been used in synthesis, usually as acyl anion equivalents <8977643, b-95MI 608-05>. Use of 1,3-dithiane derivatives is by far the most common, and the derived anions react with with a very wide variety of electrophiles <69AG(E)639, 8977643), whether or not the dithiane system is initially substituted at C-2. For example, 2-lithio-... 

The reactivity of these heterocycles towards hydrogen atom abstraction at C-2 has been shown to increase in the expected order, from 1,3-dioxane, through 1,3-oxathiane, to 1,3-dithiane. Hydrogen atom abstraction from C-2 in 4-methyl-1,3-dioxane, 2,4-dimethyl-1,3-dioxane, and 2-ethyl-4-methyl-1,3-dioxane has also been investigated <77MI 608-01 >. The radical-mediated alkylation of 2-stannyl-l,3-dithianes (67) with alkenes and enol ethers has been observed (Equation (30)) <92CL1229>. 

Chiral thiols 59 were derived from 10-camphorsulfonic add by reduction of the sulfony] chloride with lithium aluminum hydride, yielding a 1 4 mixture of enrfo/exo-diastereomers, which can be separated by chromatography60. Containing a hydroxy and a thiol functionality, 59 can be used for the formation of sulfur-containing heterocycles such as oxathianes which can react with carbanions (Section D.l.3.4.4.) or form enolates (Section D. 1.5.3.4.2.1.) and can direct osmium tetroxide catalyzed dihydroxylations (Section D.4.4.). 

NMR and X-ray studies of some spiro-l,3-oxathianes, prepared from cyclohexanones and 3-mercapto-l-propanols, indicate that the heterocyclic ring exists in the chair conformation. The system can exhibit flexible, semi-flexible and anancomeric behaviour according to the substituents present <01T8751>. 

The product of dehydrofluorination of 3Af,4//-hexafluorothiolan (248) by potassium hydroxide depends on the reaction conditions (Scheme 51). The reaction of potassium tetrafluorocobaltate(iii) with 1,4-dioxan and with 1,4-oxathian gives only traces of unsaturated heterocycles (see p, 299). ... 

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