Reaction dechalcogenation

Heavy ketones have been synthesized by several synthetic methods shown in Scheme 19 (i) the reaction of divalent group 14 element species with chalcogen sources, (ii) the reaction of dihydrometallanes with chalcogen sources, (iii) the dechalcogenation of metal polychalcogenides, (iv) the reaction of dilithiomet-allanes with dihalochalcogenides, and (v) substitution of the chloro group of heavy acyl chlorides. The methods used for the synthesis of heavy ketones are summarized in Tables 3-5. 

In 1997, Tokitoh, Okazaki and coworkers reported evidence for the generation of a kinetically stabilized 1-germaallene 20725,123. It was synthesized by two different synthetic approaches as shown in Scheme 63. One is the dechalcogenation reaction of the corresponding alkylidenetelluragermirane 205 with a phosphine reagent, and the other is the reduction of (l-chlorovinyl)chlorogermane 206 with f-butyllithium. 

The dechalcogenation reaction of tetrachalcogenametal-lolanes has proven to be an excellent synthetic approach to heavy ketones, bnt tetrachalcogenametaUolanes are not always available. In such cases, the chalcogenation of divalent species can be an alternative method. 

Scheme 5 Chalcogenation and dechalcogenation reaction possibilities of the heteroseleniranes and heterotelluriranes.

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