Oxygen- and Sulphur-containing Heterocycles

Oxygen and Sulphur-containing Heterocycles.—Dittmer and Nelsen have improved the yield of the known benzo[/ ]thiete-1,1-dioxide (281) which was prepared in six steps from (280) thermolysis of (281) gave the sultine (282). Improved 

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Unlike our initial imine disconnection which is restricted to nitrogen heterocycles (with one or two specific exceptions such as pyrylium salts, see Chapter 9), the heteroatom in the enamine or enamine-like disconnection could be divalent. Therefore this disconnection is also applicable to oxygen-and sulphur-containing heterocycles, typified by 1.24 and 1.25. 

Certain hydroboration reactions which are slow under normal conditions due to their heterogeneous nature proceed much faster under the effects of ultrasound. Several acyclic and cyclic trienes have been hydroborated with borane or triethylamineborane in THF and the stereochemistry of the products investigated. A systematic study of the hydroboration of representative heterocyclic olefins with four different reagents has been undertaken in order to establish optimum conditions for the reactions. This study has been followed by an investigation into the relative rates of reaction of 9-BBN with oxygen and sulphur containing heterocyclic olefins. ... 

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