Degree Type

Dissertation

Date of Award

1994

Degree Name

Doctor of Philosophy

Department

Chemistry

First Advisor

John G. Verkade

Abstract

This dissertation describes the development of pro-azaphosphatranes ZP(MeNCH[subscript]2CH[subscript]2)[subscript]3N as versatile useful materials in organic synthesis;Pro-imidophosphatranes MeN= P(MeNCH[subscript]2CH[subscript]2)[subscript]3N and PhN= P(MeNCH[subscript]2CH[subscript]2)[subscript]3N, their corresponding acyclic analogues MeN= P(NMe[subscript]2)[subscript]3 and PhN= P(NMe[subscript]2)[subscript]3, and their conjugate acids as well as the conjugate acid of the commercially available non-ionic base P[subscript]4-t-Bu (i.e. t-BuN=P (N=P(NMe[subscript]2)[subscript]3][subscript]3) have been synthesized. Equilibria measured by [superscript]31P NMR spectroscopy revealed the relative ordering of basicity: P[subscript]4-t- Bu > P(MeNCH[subscript]2CH[subscript]2)[subscript]3N > MeN= P(MeNCH[subscript]2CH[subscript]2)[subscript]3 N > MeN= P(NMe[subscript]2)[subscript]3 > DBU > PhN= P(MeNCH[subscript]2CH[subscript]2)[subscript]3N > PhN= P(NMe[subscript]2)[subscript]3. P(MeNCH[subscript]2CH[subscript]2)[subscript]3N (pKa of its conjugate acid = 40.7 in CH[subscript]3CN) rivals the basicity of P[subscript]4-t-Bu (pK[subscript] a of its conjugate acid = 42.1 in CH[subscript]3CN) and it is the strongest phosphorus base known to date. The above unusually strong basicity of the polycyclic bases (e.g. P(MeNCH[subscript]2CH[subscript]2)[subscript]3N and MeN= P(MeNCH[subscript]2CH[subscript]2)[subscript]3N which are ca.10[superscript]17 and at least 10[superscript]3 times stronger bases than DBU, respectively) is rationalized on the basis of bridgehead P-N[subscript] ax transannulation which effectively delocalizes positive charge. After we learned about the strong basicity of P(MeNCH[subscript]2CH[subscript]2)[subscript]3N and its utility, we improved its synthesis by using much cheaper starting materials, and easier and more economical processes;The structures of the ZP(MeNCH[subscript]2CH[subscript]2)[subscript]3N systems determined by X-ray means reveal stepwise closure of the bridgehead P-N[subscript] ax distance from 3.33 to 1.967A, concomitant with incremental opening of the average N[subscript] eq-P-N[subscript] eq angle from 104.5 to 119.6°. This observation is significant in designing derivatives of ZP(RNCH[subscript]2CH[subscript]2)[subscript]3N as useful synthetic reagents by varying the Z and R substituents; P(MeNCH[subscript]2CH[subscript]2)[subscript]3N and PhN= P(MeNCH[subscript]2CH[subscript]2)[subscript]3N have been found to be superior catalysts for the conversion of isocyanates to industrially important isocyanurates and to isocyanurate-based polymers. In contrast, O= P(MeNCH[subscript]2CH[subscript]2)[subscript]3N and S= P(MeNCH[subscript]2CH[subscript]2)[subscript]3N selectively catalyze the transformation of isocyanates to carbodiimides useful as condensing agents in the synthesis of pharmaceutically important peptides and nucleotides, and do so much more effectively than their acyclic analogues O= P(NMe[subscript]2)[subscript]3 and (MeO)[subscript]2P(S)Ph, respectively; P(MeNCH[subscript]2CH[subscript]2)[subscript]3N has also been found to be a potent deprotonation agent in the base-promoted high yield synthesis of pyrrols and oxazoles, with subsequent facile synthesis of biologically important porphyrins and [alpha]-C-acylamino acid esters, respectively. For instance, the overall yield of octaethylporphyrin has been improved by using P(MeNCH[subscript]2CH[subscript]2)[subscript]3N to 62% from previously reported yield of 5-25%. There are several advantages of our superbase P(MeNCH[subscript]2CH[subscript]2)[subscript]3N over both DBU, DBN, Proton Sponge, guanidines and the strong base P[subscript]4-t-Bu, including easier and cheaper synthesis and recovery than P[subscript]4-t-Bu, and much faster and more complete deprotonation under both low and room temperature than DBU, DBN, Proton Sponge and guanidines. (Abstract shortened by UMI.)

DOI

https://doi.org/10.31274/rtd-180813-11988

Publisher

Digital Repository @ Iowa State University, http://lib.dr.iastate.edu/

Copyright Owner

Jiansheng Tang

Language

en

Proquest ID

AAI9424265

File Format

application/pdf

File Size

231 pages

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