| Research Abstract |
A)Synthesis of Unstable Positional Isomers of Berry Pseudorotation and Their Isomerization
Spirocyclic P-H (equatorial) phosphorane 1 was prepared by the reaction of two moles of dilithiated Martin ligand and PC1_3. Monocyclic P-H (apical) phosphorane bearing R group 2 was prepared in high yield by the reaction of 1 and two moles of RU (R=methyl, n-butyl, t-butyl, benzyl, and 2, 4, 6-triisopropylphenyl), via a dianoin intermediate. By heating 2 in the presence of pyridine, spirocyclic P-R (equatorial) 0-cis phosphorane 3 , which is anti-apicophilic, was p obtained as a major product and the corresponding 0-trans phosphorane 4 was obtained as a minor product, which is more stable than 3. On the other hand, 3 was obtained in high yield when the dianion was oxidized in situ with iodine. Kinetic investigations were carried out on the enantiomerization of 3 and also on the isomerization of 3 to 4.
B)Use of Spirocyclic Phosphoranes for Wittig Reaction and the Mechanistic Invesatigation
Spirocyclic phosphorane bearing an ester group 5 was prepared by the reaction of 1 with ethyl bromoacetate in the presence of base. After deprotonation of 5, the resulting anion was reacted with a variety of aldehydes to yield the corresponding Z-olefin 6 in high yield (>98 %). As 6 has an ester group, this reaction is quite useful. All the four diastereoisomers of beta-hydroxy-alpha, beta-diphenylethylspirophosphorane 7 were prepared and the corresponding 6 coordinate phosphate 8 were observed at low temperatures as the intermediates for Wittig reaction.
The rates of Wittig reaction and the structures of the 6 coordinate intermediates were correlated.
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