Borylative cyclisation of diynes using BCl₃ and borocations

Abstract

Products from the borylative cyclisation of diynes using BCl3 is dependent on substituent effects, however, some control of product outcome is achieved using borocations or BCl3 in the presence of [BCl4]−.

Haloboration: scope, mechanism and utility

“…Although BCl 3 shows no reactivity towards internal alkynes, facile transformations between BCl 3 and 1,2-dialkynyl benzenes have been reported by the groups of Erker, Yamaguchi and subsequently Ingleson. 30,31 Presumably these proceed from the adduct between the internal alkyne and BCl 3 . In these reports, dibenzopentalenes or analogues were the major products in most cases (Scheme 13b).…”

“…In this case the dibenzopentalene 30 is only observed as the minor product (Scheme 13c). 31 Interestingly, the formation of 1,4-chloroboration products becomes favoured in other cases by the addition of an exogenous chloride donor such as [BCl 4 ] À (Scheme 14). For example, 1,2-bis(p-tolylethynyl)benzene reacts with BCl 3 affording the corresponding benzofulvene 31 and dibenzopentalene 32 in a 1 : 2 ratio.…”

Unsymmetrical Thienopentalenes: Synthesis, Optoelectronic Properties, and (Anti)aromaticity Analysis

“…Among antiaromatic subunits, pentalene is particularly interesting as this planar 8 π-electron molecule could be extended/stabilized through different fusion and substituent patterns, and the synthesis of its derivatives has advanced a lot recently . However, regardless of the available synthetic methodologies for the preparation of derivatives with unsymmetrical conjugated cores, − material properties of linear and symmetric π-extended antiaromatics are explored mostly. − Although the study of symmetric polycyclic conjugated systems is facilitated by their more straightforward syntheses in general, the departure from such structures proved to be fruitful in the case of acenes. Within the class of acenes, the introduction of asymmetry, especially by the unsymmetrical fusion of thiophenes, led to improved stability, good solubility, novel assembly modes, and interesting electronic features such as ambipolar transport properties in several cases. − …”

Borylative Cyclization of 1,6-Allenynes Driven by BCl3

“…In previous work that is especially related to this study, Erker, Yamaguchi, and co-workers discovered a novel borylative cyclization of 1,2-dialkynylbenzenes using B­(C 6 F 5 ) 3 and in one example BCl 3 to obtain dibenzopentalenes A and B . Ingleson et al presented carbocyclization/borylation of a range of diynes to produce boryl-functionalized cyclic compounds using BCl 3 . However, to the best of our knowledge, the current studies of metal-free carbocyclization/borylation mainly focus on diynes.…”

“…We recently accomplished the direct intramolecular aminoboration of sulfonamidoallenes using BCl 3 as the boron source, giving the desired products in good yields . Inspired by these results and Ingleson’s work, we decided to study the reaction between 1,6-allenynes and BCl 3 to further understand the BCl 3 -involved cyclization/borylation reactions on one hand and on the other to expand the scope of the reaction.…”