TY - JOUR
T1 - Strain-induced reactivity effects in the reaction of 2,5-dihydroxy-[1,4]-benzoquinone with diamines
AU - Hettegger, Hubert
AU - Hofinger, Andreas
AU - Rosenau, Thomas
N1 - Funding Information:
The financial support of the Austrian Biorefinery Center Tulln (ABCT) is gratefully acknowledged.
Publisher Copyright:
© 2021 Bentham Science Publishers.
PY - 2021
Y1 - 2021
N2 - The regioselectivity of the reaction of 2,5-dihydroxy-[1,4]-benzoquinone (DHBQ) with diamines could not be explained satisfactorily so far. In general, the reaction products can be derived from the tautomeric ortho-quinoid structure of a hypothetical 4,5-dihydroxy-[1,2]-benzoquinone. However, both aromatic and aliphatic 1,2-diamines form phenazines, in some cases, formally by diimine formation on the quinoid carbonyl groups, and in other cases, the corresponding 1,2-diamino-[1,2]-benzoquinones by nucleophilic substitution of the OH groups; the regioselectivity apparently does not follow any discernible pattern. The reactivity was now explained by an adapted theory of strain-induced bond localization (SIBL). Here, the preservation of the "natural" geometry of the two quinoid C–C double bonds (C3=C4 and C5=C6) as well as the N–N distance of the co-reacting diamine are crucial. A decrease of the annulation angle sum (N–C4–C5 + C4–C5–N) is tolerated well and the 4,5-diamino-ortho-quinones, having relatively short N–N spacings, are formed. An increase in the angular sum is energetically unfavorable, so that diamines with a larger N–N distance afford the corresponding ortho-quinone imines. Thus, for the reaction of DHBQ with diamines, exact predictions of the regioselectivity and the resulting product structure can be made on the basis of simple computations of bond spacings and product geometries.
AB - The regioselectivity of the reaction of 2,5-dihydroxy-[1,4]-benzoquinone (DHBQ) with diamines could not be explained satisfactorily so far. In general, the reaction products can be derived from the tautomeric ortho-quinoid structure of a hypothetical 4,5-dihydroxy-[1,2]-benzoquinone. However, both aromatic and aliphatic 1,2-diamines form phenazines, in some cases, formally by diimine formation on the quinoid carbonyl groups, and in other cases, the corresponding 1,2-diamino-[1,2]-benzoquinones by nucleophilic substitution of the OH groups; the regioselectivity apparently does not follow any discernible pattern. The reactivity was now explained by an adapted theory of strain-induced bond localization (SIBL). Here, the preservation of the "natural" geometry of the two quinoid C–C double bonds (C3=C4 and C5=C6) as well as the N–N distance of the co-reacting diamine are crucial. A decrease of the annulation angle sum (N–C4–C5 + C4–C5–N) is tolerated well and the 4,5-diamino-ortho-quinones, having relatively short N–N spacings, are formed. An increase in the angular sum is energetically unfavorable, so that diamines with a larger N–N distance afford the corresponding ortho-quinone imines. Thus, for the reaction of DHBQ with diamines, exact predictions of the regioselectivity and the resulting product structure can be made on the basis of simple computations of bond spacings and product geometries.
KW - Amines
KW - Benzoquinones
KW - DHBQ
KW - Diamines
KW - Regioselectivity
KW - SIBL theory
UR - http://www.scopus.com/inward/record.url?scp=85103816622&partnerID=8YFLogxK
U2 - 10.2174/1385272824666201209112938
DO - 10.2174/1385272824666201209112938
M3 - Article
AN - SCOPUS:85103816622
SN - 1385-2728
VL - 25
SP - 529
EP - 538
JO - Current Organic Chemistry
JF - Current Organic Chemistry
IS - 4
ER -