novel antibacterially - active compound , 1 , 2 , 8 , 8a - cyclopropabenzodipyrol - 4 - one , prepared by a novel chemical process . this compound , as well as antibacterially - active intermediates , can be used to eradicate or control susceptible bacteria , for example , b . subtilis , k . pneumonia , s . lutea , s . aureus , and m . avium . claimed compounds include those of the formula ## str1 ## wherein r 1 , r 2 , r 3 and r 4 are as defined hereinafter .