Insight into and Computational Studies of the Selective Synthesis of 6H-Dibenzo[b,h]xanthenes

Abstract

Starting from 2-hydroxy-1,4-naphthoquinone (lawsone), we synthesized eight new 6H-dibenzo[b,h]xanthene derivatives selectively under solvent-free conditions. Spectroscopic investigations confirmed that only the isomer 6H-dibenzo[b,h]xanthene was obtained in all eight cases. Computational studies provide a rationalization for the selective appearance of these isomers having as an intermediate an addition product.

Hetero-Diels–Alder Reactions of Quinone Methides: The Origin of the α-Regioselectivity of 3-Methylene-1,2,4-naphthotriones

“…The quinone methide intermediate 1a (X = O, Figure ) has been widely explored in the last decades as a versatile synthon in organic synthesis, and more recently, inspirational applications were shown in asymmetric − and natural product synthesis, , in the preparation of bioactive derivatives, − synthesis of heterocycles, free-metal catalysis, photochemical reactions, and biomedicine. − This class of intermediate is usually obtained in situ , and it can also be found as dimethane- ( 1b , X = C, Figure ), aza- ( 1c , X = N, Figure ), and thio- ( 1d , X = S, Figure ) congeners, as well as ortho ( 1 , Figure ) and para isomers ( 2 , Figure ).…”

“…Mechanistic investigation on the regio- and stereoselectivity of the quinone methide intermediate upon hetero-Diels–Alder reactions. ,, …”

“…Later, our own group investigated the reactivity of 4 R in the preparation of xanthene derivatives from lawsone (Figure c) . We have shown that, depending on the chosen reaction conditions, the concerted hetero-Diels–Alder reaction is replaced by a two-step process, in which the first step is a Michael addition with the formation of an open intermediate (experimentally isolated), followed by the cyclization/dehydration process in acidic conditions.…”

“…We have shown that, depending on the chosen reaction conditions, the concerted hetero-Diels–Alder reaction is replaced by a two-step process, in which the first step is a Michael addition with the formation of an open intermediate (experimentally isolated), followed by the cyclization/dehydration process in acidic conditions. Under these reaction conditions, ortho , para -xanthene derivatives were exclusively obtained …”

Synthesis and Cytotoxicity of N-Substituted Dibenzo[a,j]xanthene-3,11-dicarboxamide Derivatives

“…In view of the great importance of benzoxanthenes, the preparation of which has been a hot research topic, there have been many research reports in recent years [ 7 , 8 , 9 , 10 , 11 ]. So far the synthesis of dibenzo[ a , j ]xanthene has been mostly focused on the modification of the 14-position of the molecule, with other positions rarely reported in the literature, and especially the 3 and the 11 positions.…”