Direct Synthetic Route to Functionalized 1,2-Azaborinines

• Published in: Angewandte Chemie International Edition Vol. 53; no. 13; pp. 3500 - 3504
• Main Authors: Braunschweig, Holger, Geetharani, K., Jimenez-Halla, J. Oscar C., Schäfer, Marius
• Format: Journal Article
• Language: English
• Published: Weinheim WILEY-VCH Verlag 24.03.2014; WILEY‐VCH Verlag; Wiley; Wiley Subscription Services, Inc
• Edition: International ed. in English
• Subjects: Alkynes; boron; Catalysts; Chemistry; Chemistry, Multidisciplinary; cyclization; Cycloaddition; Derivatives; Esters; Formations; heterocycles; isosterism; Physical Sciences; Rhodium; Science & Technology; Strategy; ELECTROPHILIC AROMATIC-SUBSTITUTION; B-N; MOLECULAR-STRUCTURE; COMPLEXES; CRYSTAL; cyclization; HETEROAROMATIC-COMPOUNDS; FLUORIDE; isosterism; heterocycles; C-C; boron; rhodium; ELECTRONIC-STRUCTURE
• ISSN: 1433-7851; 1521-3773
• DOI: 10.1002/anie.201309707

A new catalytic synthetic route to functionalized 1,2‐azaborinines has been developed by the [2+2]/[2+4] cycloaddition reactions of di‐tert‐butyliminoboranes and alkynes in presence of a rhodium catalyst. The first examples of ferrocene‐functionalized azaborinines have been synthesized using this strategy. Moreover, the regioselectivity of this reaction can be controlled by the formation of an intermediate rhodium 1,2‐azaborete complex, which results in the isolation of the first azaborinine boronic ester. The isolation of an NH‐containing BN isostere by elimination of isobutene from an N(tBu) group under thermolytic conditions has also been achieved. Theoretical studies give further insight into the formation of 1,2‐azaborinines and the elimination of isobutene from the N(tBu) group. 2+2+2: A straightforward method to access the first examples of ferrocene‐ and pinacolatoborane‐functionalized 1,2‐azaborinine derivatives has been developed by the tandem [2+2]/[2+4] cycloaddition reactions of di‐tert‐butyliminoboranes and alkynes.