Ethanesulfenyl chloride, reaction with

The reactions of 5,6-dihydro-2-methoxy-2H-pyran (101) with 1,3-dibromo-5,5-dimethylhydantoin in ether-methanol,137 and with ethanesulfenyl chloride,138 have been described by Baldwin and Brown. The former reaction gave a 2 1 mixture of the isomers 3/3-bromotetrahydro-2a ,4a-dimethoxypyran (102) and 3a-bromotetrahy-dro-2a,4/3-dimethoxypyran (103), respectively the structures and favored conformations of the isomers are shown. The reaction of ethanesulfenyl chloride with 5,6-dihydro-2-methoxy-2H-pyran (101)... 

Ethanesulfenyl chloride (7.9 g) is added slowly to a solution of diazoacetophenone (12 g) in anhydrous ether (75 ml) at 0-5°. Nitrogen is evolved vigorously. After 2 h at room temperature the ether is removed in a vacuum. The co-chloro-co-(ethylthio)acetophenone that is produced almost quantitatively must be at once used for further reaction. The crude product (3 g) is shaken with N-potassium hydroxide solution for 2 h, then warmed for 1 h on a water-bath. After cooling, by-products are removed by extraction with ether finally mandelic acid (formed in 65 % yield) is liberated by acidification and is isolated by means of ether. 

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