Thioaldehydes S-oxides

Density functional and semiempirical AMI molecular orbital calculations have been used to investigate substituent effects on site selectivity in heterocumulene-hetero-diene4 + 2-cycloadditions between ketene imines and acroleins.The new and novel heterocumulenes a, /3-unsaturated thioaldehyde S -oxides (97) behave as both diene... 

In the sulfur literature only a few examples of thioaldehyde S-oxides 99 (mono-substituted sulfines) have been reported due to the low stability of these compounds, and they were not prepared by oxidative methods since the starting thioaldehydes are also very unstable. These problems were circumvented by using silyl thioketones249,250 as precursors which, by controlled oxidation with mCPBA, afforded the corresponding thioacylsilane S-oxides 98. These sulfines were subsequently desilylated with BU4NF (equation 104) and the stereochemistry of this process has been studied in detail408. This indirect route has been applied to the preparation of aromatic and aliphatic, not enethi-olizable, thioaldehyde S-oxides. 

The reaction of alkoxides with thioaldehyde S-oxides, generated from sul-finates, was carefully examined by Baudin et al. [163]. A number of products were isolated, formation of which was explained by carbophilic addition of the alkoxide anions. 

Thioaldehyde S-oxides behave as dienophiles with 1,3-dienes [241]. Cycloaddition involves the carbon-sulfur double bond of the heterocumulene to furnish dihydro-2H-thiapyran S-oxides (Table 6, entry 1). The cis trans product ratio was found to depend upon the initial diene/sulfine ratio. A large excess of diene selectively provided the cis cycloadducts, as a result of a stereospecific reaction of the (Z) sulfine. With a produced proportion of diene, mixtures of cis trans isomers are obtained, with a preference for the cis compound. The Italian authors have demonstrated that the slower reaction allows a (Z) to (E) isomerisation of the sulfines prior to addition. 

The dimer of trifluoromethylsulfine is obtained in the thermal generation of the sulfine from the anthracene adduct ". Also, the cyclic dimers of y-acetylenic-(3,(3-disubstituted thioaldehyde S -oxides are isolated in their generation from allenic sulfinates with vinyl... 

The corresponding 1,3-dithiolane S -oxides were prepared by oxidation of the thioacetals with m-chloroperbenzoic acid (mCPBA) and, notably, this approach has proven successful in the obtention of both thioaldehydes and thioketones. 

A novel synthesis of a-unsaturated sulfines has been introduced by Bra-verman et al. [99]. Et3N or DABCO treatment of allylic and benzylic tri-chloromethyl sulfoxides triggered the elimination of chloroform and formation of the sulfines. It must be stressed that these sulfines are thermally relatively stable, and this stands in high contrast to the corresponding thio-carbonyl compounds unsaturated thioaldehydes cannot be monitored under the same experimental conditions and have to be used at very low temperature or trapped in situ. The first synthesis of thioacrolein S-oxide was achieved by flash vacuum thermolysis of an anthracene allyl sulfoxide [100], and both isomers in a (Z E) ratio of 78 22 were characterised by NMR spectroscopy at -60 °C. 

Lactam Antibiotics.—A wealth of detail is now available on the fates of individual carbon and hydrogen atoms of valine (150) and cysteine (152) on transformation into the penicillins [as (151)]. It has been confirmed recently that cysteine gives penicillin with loss of the 3-pro-S hydrogen and it was pointed out that if oxidation of the C-3 thio-group to say a thioaldehyde occurs in the course of biosynthesis, then... 

EC 2.7.1.33) to N-(i )-4 -phosphopantothenate. Activation of the carboxylate results from the addition of P-alanine (P-alanine is formed on decarboxylation of aspartate [Asp, D], EC 4.1.1.11), by cytidylate formation (cytosine triphosphate [CTP] is followed by coupling to L-cysteine (Cys, C) (EC 6.3.2.S) to produce N-[(i )-4 -phosphopantothienoyl]-L-< steine. Oxidation to the thioaldehyde with flavin mononucleotide (EMN FMNH2) allows decarboxylation of the latter with the formation of the corresponding enol. Then, reduction with nicotinamide adenine dinucleotide phosphate (NADPH/IT NADP) (EC 4.1.1.36) leads to 4-phosphopantetheine (pantetheine 4 -phosphate). 

Hetero Diels-Alder reactions of 3,4-di-fcrf-butyIthiophene 1-oxide with thioaldehydes and thioketones take place exclusively at the syn-jt-face with respect to the S=0 bond, like the Diels-Alder reactions with ketones. Thiophosgene and adamantanethione can also react with 3,4-di-(erf-butylthiophene 1-oxide to afford the corresponding syn-tr-face products (Scheme 44) [49]. 

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