STRUCTURE OF THREE-MEMBERED RINGS WITH TWO HETEROATOMS

STRUCTURE OF THREE-MEMBERED RINGS WITH TWO HETEROATOMS... 

The scope of three-membered rings with two heteroatoms of heavier group 15 elements includes essentially heterocyclopropanes and heterocyclopropenes with two phosphorus atoms. This chapter also covers bicyclic and polycyclic molecules containing the structural motif of the rings under discussion. Such species frequently result from transformations of phosphaalkenes or oligomers. Monocyclic diphosphirane and diphosphirene derivatives are synthesized from acyclic precursors with a P-C-P linkage or alternatively via [2-1-1] cycloadditions. A few examples... 

Table 5 X-ray structures of five-membered rings with two, three, four, or five heteroatoms...

Table 1 X-Ray Structures of Compounds with Five-membered Rings and Two, Three or Four Heteroatoms ...

Eight-membered heterocyclic rings with three heteroatoms rarely occur as structural blocks of natural products and their synthetic analogues. The first example of natural 1,2,3-trithiocanes has been reported recently <2002EJ02400>. Two novel sulfur derivatives 183 and 184, one of which is a glycoside, containing substituted 1,2,3-trithiocane cycles were isolated from Perophora viridis which was collected off the Atlantic coast of North Carolina. 

With regard to optical absorptions, influence of substituents and molecular structure all observed trends follow the same rules as outlined for the (S S)+ radical cations. The most stable (S . X)+ radical cations are those intramolecular species which attain five-membered ring structures, i.e., those with, for example, three linking carbons between the two heteroatoms. Particularly interesting are the S Br bonded systems since they represent a rare example of bromine-based cationic species in organic chemistry. 

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