Sulphonation regiospecific

A further example of the use of phenyl sulphones in prenylation reactions is provided in the recent synthesis of deoxytrisporone (37) (Scheme 5)7 An interesting feature of this synthesis is the regiospecific acylation of the diol (35) with isobutyric anhydride. 

Japanese group, involves regiospecific prenylation of the sulphone (49) followed by stannolysis of the sulphonyl group and, finally, hydroxymethylation/destannylation. In the second (one-pot) synthesis, a mixture of the olefins (50) (55%) and (51) (45%) was reacted with paraformaldehyde in the presence of tin(rv)... 

Combined with the efficient and regiospecific alkylation of allylic sulphones shown in the Scheme (contrast the corresponding alkylation of allylic sulphox-ides), this method can give allylic alcohols trisubstituted on the carbon-carbon double bond. The sequence can also be adapted to open up two new routes to exocyclic a-methylene-carbinols (32) (Scheme 15)/" either by overall [1,3] transposition of oxygen from (33), or from ketones via the vinyl sulphones (34), which are isomerized to the thermodynamically favoured allylic isomers (35). 

Similarly, substituted 2-sulpholenes can be regiospecifically ring opened to give the tra 5-Y,5-unsaturated sulphones. However, the intermediate anion cannot be isolated and must be quenched with methyl iodide to prevent over reduction (Scheme 44). 

Z)-/( )-olefins (47) regiospecifically, in excellent yield (80 %). The trimethysilyl ethynynl sulphone (49) has been developed as a vinyl cation synthon by Barr and co-workers. The addition of carbanions (48) to the synthon (49) furnishes the vinyl sulphones (50), which can be converted into the adducts (51) either by... 

The tetracyclic lactone quadrone (43) is a compound that has attracted the attentions and aspirations of many synthetic chemists in recent years. The molecule is a fungal metabolite from Aspergillus terreus which is found to exhibit antitumour activity. The critical step in a synthesis of quadrone that has been described by Burke et al is the regiospecific intramolecular Michael reaction of (41), in the presence of two equivalents of morpholine and a catalytic amount of toluene -sulphonic acid (p-TSA) in hot benzene, to produce the bicyclic dional (42). Interestingly, treatment of (41) with titanium tetrachloride instead led to the spiro-compound (44) as the sole isolable product, and the dienone (45) was the major product when (41) was heated under reflux in benzene in the presence of toluene-p-sulphonic acid alone. 

Certain a-hydroxyalkylthioketals eliminate benzenethiol under treatment with a sulphonic acid to provide a regiospecific approach to a-phenylthioketones (Scheme 31), On the other hand, j8-hydroxyalkyl phenyl sulphides eliminate water, with migration of the PhS group, to yield allyl sulphides. ... 

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