Oxadisilole-Fused Isoindole

Abstract

The first synthesis of monooxadisilole-and bisoxadisilole-fused isoindoles and their [4+2]-cycloaddition reactions are reported. Deprotection of the cycloadducts leads to the formation of oxadisilole-fused benzoquinones. The structure of the bisoxadisilole-fused isoindole (2b) is confirmed by X-ray analysis.Benzyne and aryne are important intermediates in organic chemistry. 1 They have been extensively used in synthesis, for example, in the construction of functional materials. 2 Recently, we reported that benzobisoxadisiloles can serve as synthetic equivalents of benzdiynes. 3 Subsequently, the chemistry was extended to the synthesis of monooxadisilole-and bisoxadisilole-fused isobenzofurans (1a and 2a, Figure 1) and their applications in the synthesis of functional acenes. 4 Isoindole (benzo[c]pyrrole, 3) and isobenzofuran (4) are highly reactive intermediates. 2a,5,6 Although they belong to a ten-electron aromatic system, they are very reactive towards cycloaddition reactions. These isobenzo-fused five-membered ring heterocycles are highly reactive mainly because the benzene moieties of the systems have the potential to regain their full aromaticity after the cycloaddition reaction. Due to their instabilities, they usually have to be generated in situ and used immediately. To further our research program of using benzobisoxadisilole (5) and benzotrisoxadisilole (6) as synthons of benzyne and benzdiyne, 3,7 we report here the first synthesis of the room-temperature-stable monooxadisilole-and bisoxadisilole-fused isoindoles (1b and 2b) and their [4+2]-cycloaddition reactions. Figure 1The syntheses of isoindoles 1b and 2b are outlined in Scheme 1. The key reaction is the Diels-Alder/retro-Diels-Alder sequence of 9 and 10 with 3,6-di(2-pyridyl)-1,2,4,5-tetrazine (11) in chloroform at room temperature. 8 Starting materials 9 and 10 were prepared by trapping the benzynes 7 and 8 generated from benzobisoxadisilole (5) and benzotrisoxadisilole (6), respectively, with tert-butyl 1H-pyrrole-1-carboxylate. 3,8 Scheme 1 Reagents and conditions: (i) PhI(OAc) 2 , TfOH, CH 2 Cl 2 , 0°C to r.t.; (ii) n-Bu 4 NF, THF, i-Pr 2 NH, r.t.; (iii) N-Boc-pyrrole; (iv) CHCl 3 , r.t. Si Si O X Si Si O O X Si Si N-R O 2a-b 1a-b 3 isoindole a: X = O b: X = N-Boc isobenzofuran 4 -N 2 O 9: 80% i ii 1b: 43% 12 14 iii 5 7 iv 11 Py = Downloaded by: Universite Laval. Copyrighted material.

Synthesis and Atropisomeric Properties of Benzoazepine-Fused Isoindoles

“…This instability is attributed to the skewed electron density of the 10π ortho quinoid aromatic system toward the five-membered ring, consistent with the Glidewell–Lloyd rule, subsequently lowering the aromaticity of the six-membered ring . Nevertheless, with applications as fluorescent − and antiproliferative − materials (Figure a) and use as participants in numerous interesting cycloadditions (Figure b), − 2 H -isoindoles remain a valuable target for new synthetic methods.…”