Thioacetals and Related Compounds

Ketene thioacetals. a-Lithiovinyl phenyl sulfide is useful for preparation of ketene thioacetals and related compounds. ... 

Earlier work has demonstrated that pyridinium 7V-ylides and keten thioacetals and related compounds yield allyl ylides and indolizines/ " The extension of this reaction to pyridinium JV-imines provides a useful synthesis of pyrazolo-[l,5-a]pyridines (95), as shown in Scheme 21. ... 

Thiophilic addition to dithioesters followed by capture of the thioacetal anion with an electrophile provides a useful approach to the formation of carbonyl compounds such as (42) and (43), and has been elegantly employed in the total synthesis of the macrocycles ( )-maysine and ( )-4,5-deoxymaysine. Trimethyl borate has been used to convert bis(phenylthio)methyl-lithium into the keten thioacetal (45) via the boron-containing carbanion (44), as shown in Scheme 4. Bis(phenylthio)methyl-lithium and related compounds are also the key reagents in the preparation of 2-(phenylthio)-enones, 2-(phenylthio)-butadienes, a-(phenyl-... 

Gp alkylidene titanium complexes have been generally generated by decomposing dialkyl and related titanium derivatives or from treatment of thioacetals with Ti(n) compounds. Thermolyzing diazoalkane complexes permits the synthesis of non-Gp alkylidene titanium derivatives (see Section 4.05.2). 

Thioacetal anions and related anions of type (3 X, Y = SMe or SiMea) can be obtained by addition of organolithiums (RLi) to the corresponding compounds (4)." On the other hand, compounds of type (4 X = Br, SePh, or SnBua) react with Bu"Li to give o-heteroatom-substituted vinyl-lithiums (5), which in cases where Y = SPh or SePh are themselves acyl carbanion equivalents. Interestingly, the vinyl-lithium (5 Y = SPh) can also be used as a source of compounds (4 Y = SPh,... 

As described in the previous section, a-elimination of dialkyltitanocenes is of limited use for the preparation of titanocene-alkylidenes. Since thioacetals are readily available from carbonyl compounds or through alkylation of bis(phenylthio)methane and related organosulfur compounds, a thioacetal-titanocene(II) system enables the use of different types of carbene complexes. Use of appropriate thioacetals is of crucial importance in this system for the preparation of alkylidene complexes 48, the corresponding diphenyl thioacetals are the starting materials of choice. No carbene complexes are formed from dialkylthio-acetals. To generate vinylcarbene complexes 49, trimethylene thioacetals of aji-unsaturated aldehydes or l,3-bis(phenylthio)propene derivatives are employed (Scheme 4.41). The low-valent titanium species 44 is also easily prepared by the reduction of titanocene dichloride with magnesium in the presence of triethyl phosphite at room temperature. The presence of molecular sieves 4A is essential for the reproducibility of this preparation. In relatively large-scale preparations, care should be taken to control the reaction temperature [92, 93g]. 

Allylation of all these species is apparently less selective (Scheme 69, entry a), and among the various thioacetals tested 1,3-dithianes proved to be the ones which lead to the highest 0 7 The use of HMPA as a cosolvent was shown to have no effect on the regioselectivity of the allylation. However, both exclusive 7-allylation and 7-methylation have been achieved by performing the reaction in the presence of copper(I) iodide-trimethyl phosphite complex (Scheme 69, entries a-e). The reaction is best achieved with allylic chlorides, bromides and phosphate esters and does not occur with acetates, although these compounds usually react with cuprates. In all cases where isomers could be formed with respect to the electrophile, the ratio of 5n2 5n2 products was found to be greater than 0.67 (Scheme 69, entries b-e).- Related reactions have already been described with allylic sulfides (Scheme 27, see Section 1.3.2.2.4). 62.iM... 

In Scheuer (1973), investigations concerning sulphur-containing compounds in lipids of brown algae are reviewed which are biogenetically related to the dictyopterenes (Moore et al., 1972). The spectroscopically identified compounds belong to the classes of alkyl thioacetates, open-chain disulphides, and l,2-dithiepin-5-ones as well as organic tri- and tetra-sulphides. 

Related Systems. The carbanions of related 5,5-thioacetals of formylphosphonates also react with aldehydes and ketones, including Q ,/3-unsaturated aldehydes and ketones, to give the corresponding ketene 5,S-thioacetals (e.g. eq 5 ). Horner-Wadsworth-Emmons reactions of carbonyl compounds with 0,S-thioacetals of formylphosphonates [e.g. (Me0)2P(0)CH-(SMe)0Me] and mono(thio)phosphonates [e.g. (Me0)2P(0)-CH2SMe] are also known. 

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