Generation of Synthetic Equivalents of Benzdiynes from Benzobisoxadisiloles

Abstract

Linear and angular benzobisoxadisiloles 14 and 16 can serve as the precursors for stepwise generations of the syntetic equivalents of 1,4- and 1,3-benzdiynes. Benzynes generated were trapped as [4+2] cycloaddition products. Two identical or different rings can be fused to the benzdiyne equivalents. Highly substituted arenes were obtained by removing the oxygen bridges from the furan adducts. The synthesis of naphthoxadisilole 28, which can serve as the precursor of 2,3-naphthyne, is also described.

Phosphine–alkene ligand-mediated alkyl–alkyl and alkyl–halide elimination processes from palladium(ii)

“…20,21,22,23,24 Consistent with moderate Pdπ*(C=C) retro-donation, the C(2)=C(3) bond in 3 10 (1.359(3) Å) is longer than the corresponding bond in an uncoordinated analogue of 2, N-BOC-aza-benzonorbornadiene oxadisilole (1.315(4) Å). 25 In complex 4, the Pd coordination geometry is distortedtetrahedral, with the Md-Pd-P planes of the two P-alkene 15 ligands forming an 89.1° dihedral angle. Although the  2 -coordinated C=C bonds of 4 are longer (1.401(2) and 1.406(2) Å) than that of 3, as would be expected, the difference is only moderate due to the comparatively poor π-donor character of d 10 palladium species.…”

“…The effectiveness of ligand 2 is attributed, in part, to its ability to form a stable bis(phosphinealkene)Pd 0 complex, 4, together with its cis-bidentate coordination. Notably, the inclusion of an electron poor 25 phosphine moiety can also allow access to less common intramolecular pseudo-reductive elimination processes involving the coordinated phosphorus centre, resulting in phosphonium salt formation, in what can be regarded as a rare example of reductive elimination of chloromethane from Pd II . 30 Work is on-going to probe the utility of ligands such as 2 in a variety of catalytic applications.…”

4.09 Nucleophilic Coupling with Arynes

“…The hypervalent iodine aryne precursors (11 and 12) have originally been prepared from 1,2-bis(trimethylsilyl)-arenes, 74-81 whose synthesis requires severe conditions; however, an improved approach using benzoxadisilole 13 is also available (Scheme 10). [82][83][84][85][86] …”

Oxadisilole-Fused Isoindole

“…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.…”

“…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. The syntheses of isoindoles 1b and 2b are outlined in Scheme 1.…”