Hydrated Oxocarbons, II. Preparation of a New Class of Thermochromic Boron Heterocycles from Octahydroxycyclobutane or Dihydroxybutenedioic Acid

The reaction of octahydroxycyclobutane ( 2 ) with activated triethylborane gives a low yield of the thermochromic 2,6‐diethyl‐1,3,5,7‐tetraoxa‐2,6‐dibora‐4,8‐octalindione ( 5b ) by ring cleavage of 2 . Additional examples of this novel class of compounds have also been prepared directly by reacting dihydroxyfumaric acid ( 6 ) with various alkyl‐ or arylboranes. With the exception of the tert ‐butyl‐ ( 5f ) and the aryl derivatives 51 , m , the new compounds 5 undergo a temperature dependent colour change (yellow/colourless) in the solid state. The thermochromic transition temperature T th depends on the substituents and lies between −5 and 150°C.