Synthesis of Fused 1-Sila-, 1-Germa-, and 1-Selenacyclohepta-2,4,6-trienes

Abstract

A concise route to 1-sila-, 1-germa-, and 1-selenacyclohepta-2,4,6-trienes containing two fused benzo[b]thiophene units is described. Metalation of the ethylene acetal of 3-bromobenzo[b]thiophene-2-carboxaldehyde and subsequent quenching with Me 2 SiCl 2 , Me 2 GeCl 2 , or (PhSO 2 ) 2 Se gave the corresponding bis(benzo[b]thiophen-3-yl)silane, -germane, or -selenide, respectively, which were subjected to deprotection, followed by McMurry coupling, eventually affording the target compounds in good overall yields. It was also concluded that application of this approach to synthesis of related benzo-fused metallacyclohepta-2,4,6-trienes is limited to electron-deficient targets, as attempts involving electronrich substrates failed or gave only low yields at the final McMurry coupling stage.

Palladium‐Catalyzed Cross‐Coupling Reaction of Functionalized Aryl‐ and Hetero­arylbismuthanes with 2‐Halo(or 2‐Triflyl)­azines and ‐diazines

“…This reaction was performed successfully on a gram scale, and no decomposition was noticed after 1 month upon storing the reagent at room temperature in air. A limited number of organometallic reagents bearing formylaryl groups have been described in the literature, [28,29] and to the best of our knowledge, only three reports of the hydrolysis of acetals directly on the organometallic reagent could be found, those being with germanium, [30] antimony, [31] and mercury. [32] To unequivocally confirm the structure of this new organometallic reagent, compound 20 was recrystallized.…”

MPHT‐Promoted Bromocyclization of ortho‐Substituted Arylalkynes: Application to the Synthesis of 2‐Substituted 3‐Bromobenzofurans and ‐Benzo[b]thiophenes

“…at room temperature for 3 h, we were pleased to observe the formation of 1,2-ethenyl bis(benzofuran) 6, which was isolated in a moderate 21 % yield, despite the fact that the reaction conditions were unoptimized (Scheme 2). Further cyclization of 6 (or its benzothiophene analog) would provide a set of fused thiepins, [20] as well as 1-sila-, 1-germa-, 1-selenacyclohepta-2,4,6-trienes [21] of biological interest.…”

New syntheses of unsymmetrical thiepins and their selenium analogues

“…8,9 The only available approach to compound 4 is based on the metalation of 2-bromobenzaldehyde acetal (5) 10,11 using n-BuLi, followed by introduction of elemental selenium, but this gave only a very low yield of product (20%). 12 In order to improve the yields of compounds 3 and 4, a modified procedure was used instead, wherein the solvent was changed from THF to diethyl ether, and an oxidative workup step was introduced (Scheme 1).…”

“…7 As such previous approaches require rather complex starting materials and numerous steps, it was envisaged that more convenient access to unsymmetrical thiepin systems could be gained using a new route based on our previous work in this field, which resulted in syntheses of new symmetrical thiepins, 8 as well as some novel related cycloheptatrienes featuring other heteroatoms, namely selenium, silicon, and germanium. 9 …”