Sulphur heterocycles, formation from

From Other Sulphur Heterocycles. The reaction of (46) with 2 eq. of bromine in CHjC gave (47), except for, (46d), which directly gave (48a). Further bromination of (47a) gave (48b). The formation of (47) from (46) has been assumed to proceed via (49) to (53).15 The reaction of (54) with chloroacetone under basic conditions unexpectedly yielded (55) in 44% yield.16 Photolysis of (56) gave tetraphenylthiophen, tetraphenyl-1,4-dithiine, diphenyl-acetylene and sulphur. The products are assumed to be formed via the dimer (57) and (58), which were isolable under appropriate conditions. Photolysis of (56) in the presence of dimethyl acetylenedicarboxylate gave a 17% yield of dimethyl 2,5-dif)henyl-thiophen-3,4-dicarboxylate.17 The reaction of (59) with diphenyl-acetylene at 300°C gave tetraphenylthiophen.1 ... 

Hydrogen sulphide is a key intermediate in the formation of many heterocyclic sulphur compounds. It is produced from cysteine by hydrolysis or by Strecker degradation ammonia, acetaldehyde and mercaptoacetaldehyde are also formed (Scheme 12.4). All of these are reactive compounds, providing an important source of reactants for a wide range of flavour compounds. Scheme 12.6 summarises the reactions between hydrogen sulphide and other simple intermediates formed in other parts of the Maillard reaction. 

When the pentamer (66) reacts with alkoxide anions at low temperatures (-30 to -40°C), then the products of kinetic control (102) are isolated, whereas at higher temperatures, thermodynamic control prevails and the products (103) are obtained [131,132] (Scheme 68). Similar observations have been made with sulphur nucleophiles [132], and complex products are obtained with amines, including the formation of heterocycles [132]. Reaction of (66) with ethyl acetoacetate gave a pyran derivative (104) in a reaction that may be rationalised as shown in Scheme 69 [133]. In an analogous way.furan derivatives are formed from perfluoro-2-butene and -cyclohexene in base-induced reaction with 1,3-dicarbonyl derivatives [133]. 

Heterocyclic This designates a closed-ring structure, usually 5-membered or 6-membered, in which one or more of the atoms in the ring is an element other than carbon (e.g. sulphur, nitrogen, etc.). Homopolymerisation The process of formation of synthetic high polymers from a single monomer. 

Heterocycles containing One Sulphur Atom Thiopyrans. - A convenient synthesis of 2-phenylthiopyran-4-one (217) has been developed from methyl styryl ketone and ethyl formate. The enolate... 

Isolation of the hydrocarbons from other lipids The total lipid extract may be subjected to removal of elemental sulphur by passage through an activated copper column (Blumer, 1957) and then to chromatographic separation on adsorbent columns or thin layer plates. For column chromatography, silic el is used with a short alumina bed on the top of the silic el. Both adsorbents should be partially deactivated by the addition of water (2—5%) to prevent the formation of artifacts (Blumer, 1970). Elution with a non-polar solvent such as hexane or pentane and subsequently with mixtures of non-polar and polar solvents, e.g. benzene and methanol, permits the isolation of several fractions containing saturated, unsaturated, aromatic hydrocarbons and more polar compounds (methyl esters, alcohols, acids, phenols and heterocyclic compounds). The interference from esters encountered in the isolation of aromatic hydrocarbons can be avoided prior to separation by saponification of the esters of fatty acids, which are easily removed. 

Other work on four-membered heterocycles containing one sulphur atom includes a study of the vacuum-u.v. photodecomposition of thietan 1,1-dioxide and the formation of a thietanone from a xanthate and diphenylketen, and reports of several thiets. There is evidence that photolysis of (107) in a matrix at 77 K leads to the o-thiobenzoquinone (108), which is interconvertible with the... 

A variety of thioketones have found applicability in the synthesis of heterocyclic compounds. Chloro-thioacetone reacted with trialkoxy-phosphines to give thiirans. Thiophens have been prepared from mono-thio-j3-diketones, j8-thioketo-esters, > and from a-thioketo-acids. a-Thioacyl-y-lactones and -thiolactones rearrange in acid alcoholic solution to give dihydrofurans and dihydrothiophens, respectively. The simultaneous action of carbon disulphide, sulphur, and triethylamine on aliphatic thioketones gave mixtures of l,2-dithiole-3-thiones and 1,3-dithiole-2-thiones. The formation of thio-ozonides (1,2,4-trithiolans) by... 

The interaction of enamines with sulphur in conjunction with carbon disulphide, isocyanates, or isothiocyanates results in the production of sulphur-containing heterocyclics. Cyanamide has now been shown to participate in this reaction. Treatment of enamines of type (24) with sulphur and cyanamide at room temperature in ethanol produces a range of 2-aminothiazoles (27) in 30—70% yield no catalyst is required. Initial formation of the thiolated intermediate (25) is probably followed by addition of cyanamide, yielding (26) elimination of amine finally produces the observed thiazoles (27). Since AW-dialkylcyanamides do not undergo this reaction, cyanamide may react as the tautomeric carbodi-imide. An actual example of the reaction employing the enamine derived from cyclohexanone and morpholine is also shown [(28) - (29)]. ... 

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