Substituents sulphinyl

Exchange of organic substituents at the sulphinyl sulphur atom. . 361... 

Addition of the dianion of /5-sulphinylcarboxylic acids to carbonyl compounds leads to the formation of the corresponding hydroxy derivatives which undergo spontaneous cyclization to give y-lactones440. Bravo and coworkers have found that when optically active ( + )-(R)-3-(p-toluenesulphinyl)propionic acid 426 is used for this reaction, the corresponding diastereoisomeric / -sulphinyl-y-lactones 427 are formed in a ratio which is dependent on the substituents in the carbonyl component441,502 503 (equation 256). 

Reaction of optically active a-sulphinyl acetate 298a with prochiral carbonyl compounds proceeds with a high asymmetric induction - , the degree of which depends on the nature of substituents at the carbonyl group (equation 252 Table 22) . The jS-hydroxy sulphoxides 422 formed may be transformed to optically active p-hydroxycarboxylic esters 423 (equation 253) and optically active long-chain lactones 424 99 (equation 254). Corey and coworkers have used this method to introduce a chiral centre at C-3 in their synthesis of maytansin °°, and Papageorgiou and Benezra for the synthesis of chiral a-hydroxyalkyl acrylates 425 ° (equation 255). 

The [4 + 2] cycloaddition of a-phenylselenopropenoyl trimethylsilane (75) with 2,3-dimethylbuta-1,3-diene is unusual in that a significant portion of product mixture consists of the hetero-Diels-Alder dihydropyran adduct 76. The phenylselenenyl substituent appears to be responsible for this unusual pattern of reactivity, since propenoyl trimethylsilane gives only the expected regioisomer (77, X = H) (Scheme 116)14. a-Selenenyl substituted a,/l-unsaturated acyl silanes such as 75 were used to prepare a series of substituted dienes in excellent yields through the addition of a-sulphinyl carbanions, Brook rearrangement and expulsion of sulphinate, in a reaction pathway recognisably more typical of acyl silanes (Scheme 117). 

A somewhat different type of approach to chiral aldol products uses a sulphinyl group as a removable chiral auxiliary. Although the chemical yields were modest, the optical purities of the products (54 - 78%) must be regarded as impressive for the difficult case of chiral 8-hydroxy ketones with no a-alkyl substituent (Scheme 35).17 ... 

The position of the S=0 band is dependent on the electronegativity of the attached group. Electronegative substituents tend to raise the frequency since they tend to stabilize the form S=0 rather than S+-0". Hence, the frequency of the S=0 stretching vibration increases in the following order sulphoxides < sulphinic acids < sulphinic acid esters sulphinyl chlorides... 

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