Epoxyanthracene Derivatives and Dicarbonylation on Benzene Ring via Hexadehydro-Diels–Alder (HDDA) Derived Benzynes with Oxazoles

Abstract

Here we report a capture reaction of hexadehydro–Diels–Alder derived benzyne with various substituted oxazoles. With methyl, hydrogen or phenyl as the substituent at 2-position of oxazole, we obtained epoxyanthracene derivative and dicarbonylation on benzene ring. The reaction does not require any catalyst and additive. The mechanism behind the reaction was investigated. The obtained polycyclic product structure has potential application value in optoelectronic materials. The availability of dicarbonylated arene implies the uniqueness of HDDA benzyne reaction compared with traditional benzyne.

2:1 Adducts Arising from Reactions between Benzynes and 1,3,4-Oxadiazoles

“…25) to produce an isobenzofuran species that is captured by a second molecule of benzyne. 11 To gain an understanding for the stark difference between the different modes of reaction of compound 13 with oxadiazole 14 versus oxazole 24 (i.e., no [4 + 2] product observed using compound 14), we computed the transition structures for the possible concerted [4 + 2] cycloadditions of each pair (Figure 6 and larger PES in the Supporting Information). E act for the (unobserved) oxadiazole Diels− Alder reaction with compound 13* (a slightly simplified version of benzyne 13; the structure of compound 13* is given in Figure 7) via transition state TS5 was 14.4 kcal mol −1 compared to E act of 10.5 or 9.9 kcal mol −1 for the oxazole via transition state TS6a or TS6b, respectively.…”

“…These arise from the loss of HCN via a retro-Diels–Alder reaction of an initial adduct (cf. 25 ) to produce an isobenzofuran species that is captured by a second molecule of benzyne …”

“…However, we wondered whether the steric bulk of the HDDA benzyne was also playing a significant role in influencing the novel modality of the reaction. We therefore reacted triyne 12 with 2,5-diphenyloxazole ( 24 ), a trapping agent that closely mimics the steric environment of 2,5-diphenyl-1,3,4-oxadiazole ( 14 ) (Figure ) and that is known to trap both simple, unhindered benzynes as well as HDDA benzynes via initial [4 + 2] cycloaddition. The two regioisomeric epoxyanthracene products 26a and 26b were isolated in a combined 67% yield.…”