Sulphinates synthesis

The synthesis of chiral dialkyl sulphoxides of high optical purity from dia-stereoisomeric alkanesulphinates has a serious limitation because the sulphinates are not... 

Further utility of the Andersen sulphoxides synthesis is demonstrated by the preparation of optically active unsaturated sulphoxides which were first prepared by Stirling and coworkers359 from sulphinate 276 and the appropriate vinylic Grignard reagents. Later on, Posner and Tang360 prepared in a similar way a series of ( )-l-alkenyl p-tolyl sulphoxides. Posner s group accomplished also the synthesis of (+)-(S)-2-(p-tolylsulphinyl)-2-cyclopentenone 287, which is a key compound in the chiral synthesis of various natural products361 (equation 159). 

The Andersen sulphoxide synthesis is general in scope and a large number of chiral alkyl aryl and diaryl sulphoxides became available from (—)-(S)-276 and other optically active sulphinates " (Table 16). 

An alternative approach to the synthesis of 1,3-dienes is by elimination of benzene-sulphinic acid from homoallylic sulphones under basic conditions. This method has been used for the synthesis of a pheromone constituent of the codling moth (equation 67)109. 

Using a soliddiquid two-phase system of the sodium arenesulphinite in 1,2-dimethoxyethane, or in the complete absence of a solvent, permits the use of less reactive haloalkanes [3,4], This is a particularly good method for the preparation of sulphones where the sulphinic acid salts are readily available and, in addition to the synthesis of the tolyl sulphones listed in Table 4.28, it has been used to prepare phenyl sulphones [3]. Phenyl sulphones have also been prepared in good yield using a polymer supported catalyst [5] (Table 4.29). As the system is not poisoned by iodide ions, reactive iodoalkanes can be used and there is the additional advantages in the ease of isolation of the product and the re-use of the catalyst. 

Sultines (cyclic sulphinate esters) can be readily oxidized to sultones by hydrogen peroxide or potassium peroxysulphate. The first example of such a synthesis was reported by King and De Mayo and their associates69 who prepared l,2-oxathiole-2,2-dioxide (22)... 

Chromones.- Enamines have previously been converted into chromones and in another approach, the enamine (104) reacted with thionyl chloride to give the chromone (105 n=2) in moderate yield. The sulphinic acid was readily oxidized to the sulphonic acid (105 n=3) by 3-chloroperoxybenzoic acid.110 A convenient synthesis has been described of 2-methylchromene-4-thione in 57% yield from 4-(2-hydroxyphenyl)butane-1,3-dione.111 The t-amino-methylchromones (106) have been synthesized and shown to be central nervous system depressants. A new synthesis of 2-substituted chromones (including flavones) uses 2-acetoxyphenacyl bromide (107) which is converted into its phosphorane (108). Heating this with an alkanoyl or aroyl chloride or anhydride in pyridine gave good yields of the chromone (109).113... 

After the elimination, water-soluble sulphinates can be readily recovered, in shcirp contrast to the alternative Wittig reaction which inevitably suffers from difficulty in recycling phosphine oxide. The sulphone methodology was applied for the first time to the synthesis of vitamin A derivatives by Julia and has been developed as the Rhone-Poulenc process [1-3]. The initial design to prepare retinoic acid (1) involves coupling between the C 15-bromide 2 and the C5-sulphone 3, followed by treatment of the resulting carboxy sulphone 4 with base (Scheme 1) [1]. 

The alkylation/elimination methodology is also applicable to synthesis of carotenoids. The basic strategies for the apo-8 -p-carotenoids [ 12] and for p,p-carotene (3) [ 13] are depicted in Schemes 10 and 11. Vitamin A acetate (10) was reacted with sodium /7-phenoxybenzene-sulphinate to give the sulphone 31. The reaction of 31 with the bromo compounds 32 and 33, respectively gave the apocarotenoic acid ester 34 and the corresponding aldehyde 482. 

In view of their importance in asymmetric synthesis new routes have been developed to chiral sulphoxides and related species. Sulphinates, useful as precursors of chiral sulphoxides, have been prepared in 40-70% enantiomeric excess and the synthesis and dieno-philic properties of the isomeric sulphinyl acrylates (2l8) and (219) (Ar = 4-MeCgH ) have been described. ( )-Vinyl sulphoxides have been prepared in high optical purity via 1-alkynyl... 

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