Efficient and Complementary Methods Offering Access to Synthetically Valuable 1,2‐Dibromobenzenes

Abstract

1,2‐Dibromobenzenes are highly valuable precursors for various organic transformations, in particular, reactions based on the intermediate formation of benzynes. This report describes short sequences for the synthesis of various derivatives based on regioselective bromination, ortho‐metalation, and halogen/metal permutations. 1,2‐Dibromo‐3‐iodobenzene (2f), 1,2‐dibromo‐4‐iodobenzene (4c), and 2,3‐dibromo‐1,4‐diiodobenzene (5e) act as intermediates in these syntheses.

Regioselectivity in the Aryne Cross‐Coupling of Aryllithiums with Functionalized 1,2‐Dibromobenzenes

“…The 1,2-dibromobenzene derivatives 1a-c,m are commercially available and the 1,2-dibromobenzenes 1d-i,k-l,o-s were synthesized ac-cording to methods developed in our laboratory or described in the literature. [17] (2,3-Dibromo-4-methylphenyl)trimethylsilane (1j): Lithium tetramethylpiperidide (LTMP; 20.0 mmol) was added dropwise to TMSCl (2.54 mL, 20.0 mmol) and 1,2-dibromo-3-methylbenzene (2.50 g, 10.0 mmol) in anhydrous THF (10 mL) under Ar at -78°C. LTMP was prepared in anhydrous THF (10 mL) at 0°C by deprotonation of tetramethylpiperidine (3.37 mL, 20.0 mmol) with BuLi (20.0 mmol) in hexane (12.5 mL).…”

“…Very recently our group overcame these restrictions and developed a straightforward access to 1,2-dibromobenzenes that could be functionalized at will at any vacant position. [17] However, in contrast to the addition of an aryllithium precursor to a symmetrical benzyne, we have now studied the regioselectivity of the addition to dissymmetrical benzynes ( Figure 2) and found reaction conditions that allow "aryne" coupling with complete control of regioselectivity. These results will be reported in this paper.…”

Efficient Bottom‐Up Preparation of Graphene Nanoribbons by Mild Suzuki–Miyaura Polymerization of Simple Triaryl Monomers

“…Starting from inexpensive 1,2-dibromobenzene, ab rominedirected ortho lithiation/silylation was adopted through modificationo faknownp rocedure [9] to access 1,4-disilane 2 (Scheme 2). Subsequent Suzuki-Miyaura coupling followed by bromination with Br 2 afforded1 ,4-dibromo triaryl 5,w hich can potentially serve as am onomer for Yamamoto polymerization.…”

Improving the Halogen–Magnesium Exchange by using New Turbo‐Grignard Reagents

“…Thus, the treatment of 81 with i PrMgCl at −78 °C followed by the addition of the dioxaborolane 82 provides the boronic ester 83 in 53 % yield. Subsequent addition of 27 at −78 °C leads to a selective I–Mg exchange furnishing, after the addition of 82 , the dibromo‐derivative 84 in 87 % yield (Scheme ) . α‐Hydroxyacetophenones, which are useful intermediates for the generation of chiral molecules, have been prepared by McLaughlin using turbo‐Grignard reagent 27 .…”