Regioselective Catalytic and Stepwise Routes to Bulky, Functional‐Group‐Appended, and Luminescent 1,2‐Azaborinines

Abstract

The regioselective syntheses of 1,2-azaborinines is achieved using an unsymmetrical iminoborane through both catalytic and stepwise modular routes. The 1,2-azaborinine ring can be selectively functionalized in the 4- and/or 6-position through control of the stepwise reaction sequence, allowing access to vinyl-functionalized and redox-active, luminescent, donor-functionalized 1,2-azaborinines. The electrochemistry and photochemistry of a tetraarylamine-substituted 1,2-azaborinine are studied. Cyclic voltammetry of this compound, relative to a non-B,N-substituted reference molecule, showed an additional oxidation wave assigned to the oxidation of the azaborinine ring, while emission spectroscopy indicated that the azaborinine was significantly more fluorescent than the reference.

Recent Developments in Azaborinine Chemistry

“…1,2‐di‐ tert ‐butyl‐4,6‐diferrocenyl‐1,2‐azaborinine 6a could be pyrolyzed at 200 °C under vacuum to yield the 1,2‐di‐ tert ‐butyl‐4,6‐diferrocenyl‐1‐hydro‐1,2‐azaborinine. Similarly, unsymmetrically 1,2‐substituted 1,2‐azaborinines additionally substituted at the C(4) through C(6) position(s) were obtained when the iminoborane Mes‐B≡N t Bu was used to form the azaborete‐rhodium intermediate, which then reacted with various alkynes, yielding products 6c–m (Scheme ) …”

“…Our reports on the synthesis of azaborinines, disclosed the isolation of an intermediate 1,2‐azaborete complex containing a four‐membered BNC 2 R 4 ring bound to a rhodium center in an η 4 fashion. These azaborete complexes were the first of their kind reported in the literature, and since then a range of 1,2‐azaborete complexes has been prepared by the combination of an iminoborane, an alkyne and the [( i Pr 3 P) 2 RhCl] 2 dimer.…”

DFT Studies on the Reactions of Boroles with Alkynes

“…Recently, reactive boroles have been employed to generate boron heterocycles from their reactions with acetonitrile, azides, sulfur, CO, and other nucleophiles . With this synthetic approach, boron heterocycles, such as borepin and 1,2‐azaborinine compounds,, have been successfully prepared.…”

Acetylene in Organic Synthesis: Recent Progress and New Uses

“…Three-component cycloaddition reactions of acetylene were also described [ 129 , 130 , 131 , 132 ]. Rhodium-catalyzed [4 + 2 + 2]-cycloaddition of dienynes and acetylene gave rise to oxygen- and nitrogen-containing polycyclic cyclooctatrienes in moderate to good yields ( Scheme 52 ) [ 129 ].…”