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Effect on chair-chair equilibrium of 3-substituted-1,3,2-oxazaphosphorinanes of replacement of Me2N substituent on phosphorus by isoPr2N

✍ Scribed by Nasreen N. Mullah; Alan E. Sopchik; Wesley G. Bentrude

Publisher: John Wiley and Sons
Year: 1996
Tongue: English
Weight: 886 KB
Volume: 7
Category: Article
ISSN: 1042-7163
DOI: 10.1002/(sici)1098-1071(199611)7:6<461::aid-hc9>3.0.co;2-b

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✦ Synopsis

The chair-chair conformational equilibria (A + B) of a series of 1,3,2-dioxaphosphorinanes featuring threecoordinated phosphorus substituted with a n isoPr2N group (1-6) have been studied by 'H N M R spectroscopy. Substituents at N(3) included Ph, Me, and isoPK Compared to the analogous series with a n Me,Ngroup on phosphorus, 1-6 populate the chair conformation B with R,N equatorial to a greater extent. This is interpreted to mean that conformer A is more destabilized by the greater steric size of isoPr2N than is conformer B. Thus, the repulsive interactions between equatorial Me,N and the substituent on N3, believed to be responsible for depopulation of B that results in an unexpectedly high population of A with Me,N on phosphorus, is overcome by destabilization of A by the axial isoPr,N. The apparent size effect of substituents on N 3 in destabilization of B follows the order Ph > isoPr > Me, as observed earlier for the series with a Me,N group on phosphorus.

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