Synthesis and Reactions of Strucuturally New Intermediates of the Witting-type Reactions Contaning Group 13,14, and 15 Elements

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1.The first tetracoordinate 1,2-oxaboretanide has been synthesized by treatment of the corresponding beta-hydroxyalkyldimesitylborane with KH in the presence of 18-crown-6. The X-ray crystallographic analysis has shown that it has a distorted tetrahedral structure. Thermolysis has given the corresponding olefin, indicating that it is an intermediate of the boron-Witting reaction. On heating trimethylsilyl ether of benzaldehyde adduct undergoes the Witting-type reaction to give the corresponding olefin. 2.A pentacoordinate 2-Phenyl-1,2-oxagermetanide bearing the Martin ligand has been similarly obtained from the corresponding beta-hydroxyalkylgermane as an intermediate of the germanium-Peterson reaction. 2-Methyl derivative has also been given. The X-ray crystallographic analysis has shown that they have a distorted trigonal bipyramid (TBP) structure. Before olefin formation reaction takes place, thermal isomerization has been observed for both 2-phenyl and 2-methyl-1,2-oxagermetanides, kinetic study indicating that the isomerization proceeds via a different mechanism each other. 3.2,2,6,6-Tetraphenyl-and 2,2,6,6-tetrakis(p-chlorophenyl)-1,5-dioxa-4lambda^5-phoshaspiro[3.3]heptanes have been synthesized by the cyclization and dehydration reaction of the corresponding dihydroxyphosphine oxides with Appel reagent (Ph_3P-CCI_4). Although they not isolable, three diastereomers of 3,7-dimethyl derivative of the latter have been isolated. The X-ray crystallographic analysis has shown that two diastereomers have a distorted TBP structure, but one has a distorted tetragonal pyramid structure. Their thermolysis has given two molar equivalents of the corresponding olefin. The first example of pentacoordinate 1,2-azaphosphetidines has also been synthesized and C-apical and N-equatorial pseudorotamer has been observed for the first time. These results have been partially published as short communications.