Thio- and Seleno-Carbonyl Compounds

The diene (9) undergoes Diels-Alder reactions readily and is, therefore, a useful synthon for a-phenylthiocycloalkanones the observed regiospecificity of the Diels-Alder annelations is due to the influence of the phenylthio-group.  

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An extensive review of the hetero-Diels-Alder reactions of 1-oxabuta-1,3-dienes has been published. Ab initio calculations of the Diels-Alder reactions of prop-2-enethial with a number of dienophiles show that the transition states of all the reactions are similar and synchronous.Thio- and seleno-carbonyl compounds behave as superdienophiles in Diels-Alder reactions with cyclic and aryl-, methyl-, or methoxy-substituted open-chain buta-1,3-dienes.The intramolecular hetero-Diels-Alder reactions of 4-benzylidine-3-oxo[l,3]oxathiolan-5-ones (100) produce cycloadducts (101) and (102) in high yield and excellent endo/exo-selectivity (Scheme 39). A density functional theoretical study of the hetero-Diels-Alder reaction between butadiene and acrolein indicates that the endo s-cis is the most stable transition structure in both catalysed and uncatalysed reactions.The formation and use of amino acid-derived chiral acylnitroso hetero-Diels-Alder reactions in organic synthesis has been reviewed. The 4 + 2-cycloadditions of A-acylthioformamides as dienophiles have been reviewed. ... 

Sila-, Thio-, and Seleno-carbonyl Compounds.—A new synthesis of a-sila-ketones involves the monohydroboration of silylalkynes with dichloroborane. This reaction occurs regio- and stereo-specifically to give vinylboronic esters which may be oxidized to the corresponding a-sila-ketone (Scheme 15). ... 

Thio- and Seleno-carbonyl Compounds Thioaldehydes etc. Se analogues 149... 

Thio- and Seleno-Carbonyl Compounds.—a-Arylthio- and a-alkylthio-carbonyl compounds have become established synthons in organic chemistry. A new regio-specific route to a-phenylthioketones (an alternative to direct thiolation of enolate anions ) involves the treatment of an aldehyde with a lithio a,a-bisthiophenyIal-kane, and aqueous acid-promoted decomposition of the adduct (Scheme 8). Alternatively, trifluoroacetic acid treatment of the bisphenylthioalkanols leads to the elimination of diphenyl disulphide and the formation of simple ketones in the latter sequence, the lithiated bisphenylthioalkanes act as acyl anion equivalents (Scheme 8). ... 

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