The Mitsunobu reaction in which a phosphorus compound and an azodicarboxylic acid diester are used to carry out dehydration condensation have been employed as a useful synthetic reaction for producing medical drugs and the like. The Mitsunobu reaction is known as a dehydration condensation reaction between alcohols and a variety of acidic compounds such as carboxylic acid compounds, phenolic compounds, imide compounds, phosphoric acid compounds and hydrogen azide, and it is also known that use of an optically active alcohol as a starting material can provide the desired product as a result of complete stereo inversion (see Non-patent Document 1).
However, known azodicarboxylic acid dimethyl ester, azodicarboxylic acid diethyl ester, and azodicarboxylic acid diisopropyl ester have the following disadvantages.
(1) Since these compounds are liquid at ordinary temperatures, purification by distillation must be performed. However, azo compounds are generally unstable in heat, and it is therefore dangerous to heat these compounds. In fact, it has been demonstrated that caution should be exercised when synthesizing azodicarboxylic acid dimethyl ester and azodicarboxylic acid diethyl ester (see Non-patent Document 2).
(2) For example, when a Mitsunobu reaction in which dehydration condensation is carried out in combination with a phosphorus compound, or an oxidation reaction is performed, 1,2-hydrazinedicarboxylic acid diester is produced as a by-product; this compound is insoluble in water and moderately dissolves in an organic solvent, and therefore, many processes are required to remove or separate this compound from the product.
Therefore, at present, conventional azodicarboxylic acid diester compounds are not industrially advantageous compounds due to the above-described disadvantages.    Non-patent Document 1: Synthesis, 1, 1 (1981) (Syntheis, 1st ed., p. 1, 1981)    Non-patent Document 2: Org. Synth. Coll., Vol. IV, 411 (1963)
USPTO Backgrounds
USPTO Backgrounds