Asymmetric addition of chiral boron-ate complexes to cyclic iminium ions

Enantiospecific sp2–sp3 coupling of secondary and tertiary boronic esters

“…Figure 3, Path B). 38,48 In order to promote nucleophilic reaction of the boronate complex at the aromatic ring rather than the sp 3 centre (as required for an arylation process) we reasoned that more electron rich aromatics were required and initially selected furan. These boronate complexes reacted with NBS at the aromatic ring and, following 1,2 migration and elimination, gave the furyl-coupled product stereospecifically as illustrated in Figure 1.…”

Simple Access to Elusive α-Boryl Carbanions and Their Alkylation: An Umpolung Construction for Organic Synthesis

“…This reactivity paradigm would be in line with studies by Aggarwal on the stereospecific (invertive) reaction between electrophiles and secondary boron ate complexes. 16 , 17 While related deborylative alkylations have been accomplished with geminal bis(dialkyl)boranes, 18 only two examples involving bis(pinacol)boronates have been described and they were both limited to benzylic substrates and employed strong base promoters under cryogenic conditions. 19 In this report, we describe an alkoxide-promoted deborylative alkylation of geminal boronates that applies to aliphatic primary, secondary, and tertiary derivatives and that can enable highly hindered C–C couplings between geminal boronates and alkyl halide electrophiles.…”

Nucleophilic Dearomatization of Activated Pyridines

“…As expected, when 4-methoxypyridine was engaged in the dearomatization process, a 4-dihydropyridone was obtained after acidic work-up (Scheme 10). Aggarwal explored the addition of configurationally stable chiral lithiated boronic esters, a class of nucleophiles developed by his group, to N-acylpyridinium salts, activated by an EWG (electron-withdrawing group) group at the 3-position [34]. The reaction proceeded with high diastereoselectivities and complete retention of the enantioselectivity values of the starting boron-ates (Scheme 11).…”

“…The reaction proceeded with high diastereoselectivities and complete retention of the enantioselectivity values of the starting boron-ates (Scheme 11). The unusually high diastereoselectivity observed was explained by considering a strong cation-π interaction between the cationic heterocycle and the electron-rich benzylic boron-ate complex, with concomitant minimization of steric interactions between the Aggarwal explored the addition of configurationally stable chiral lithiated boronic esters, a class of nucleophiles developed by his group, to N-acylpyridinium salts, activated by an EWG (electron-withdrawing group) group at the 3-position [34]. The reaction proceeded with high diastereoselectivities and complete retention of the enantioselectivity values of the starting boron-ates (Scheme 11).…”