Dimesitylboryl-ended oligothiophene with tetrazine as core: Synthesis, structure and Diels–Alder reactivity

A dimesitylboryl-ended oligothiophene with tetrazine as core (BTz) was synthesized and its reactivity and spectral changes toward trans-cyclooctene ((4E)-TCO-OH), cis-cyclooctene and bicyclo[6.1.0]non-4-yn-9-ylmethanol were comprehensively studied. The fluorescence intensity of BTz was enhanced up to more than 100 times upon bioorthogonal reaction with (4E)-TCO-OH. In addition, the first crystal structure of isolated product of tetrazine derivative with cyclooctene was determined, which clearly confirmed a dehydrogenation occurred after Diels–Alder reaction under ambient conditions.