Reductive Carbocyclization of Homoallylic Alcohols to syn‐Cyclobutanes by a Boron‐Catalyzed Dual Ring‐Closing Pathway

Abstract

The organoborane-catalyzed reductive carbocyclization of homoallylic alcohols has been developed by using hydrosilanes as reducing reagents to provide a range of 1,2-disubstituted arylcyclobutanes. The reaction proceeds in a cis-selective manner with high efficiency under mild conditions. Mechanistic studies, including deuterium scrambling and Hammett studies, and DFT calculations, suggest a dual ring-closing pathway.

B(C6F5)3-catalyzed dehydrogenative cyclization of N-tosylhydrazones and anilines via a Lewis adduct: a combined experimental and computational investigation

“…Tris(pentauorophenyl)borane has recently emerged as a powerful Lewis acid catalyst. [1][2][3] The strong Lewis acidity 2,3 at the boron center allows us to establish a wide range of organic transformations via C-B, [4][5][6] C-C, [7][8][9][10] C-N, 11,12 C-O 13,14 and C-Si [15][16][17][18] bond formations. Pioneered by Stephan and Erker, B(C 6 F 5 ) 3 has gained popularity in frustrated Lewis pair (FLP) chemistry which encompasses widespread applications in organic reactions.…”

Reversibility and reactivity in an acid catalyzed cyclocondensation to give furanochromanes – a reaction at the ‘oxonium-Prins’ vs. ‘ortho-quinone methide cycloaddition’ mechanistic nexus

“…Intrigued as to how this would manifest itself in experimental data, we set out to determine a Hammett correlation for the reaction 24–27. To this end, six homoallylic alcohols with para -substituents of varying electronic demand from p -OMe to p -Cl ( 2a–2f ) were each subjected to the reaction conditions and the reactions monitored by 1 H NMR.…”

Defunctionalisation catalysed by boron Lewis acids

“…Later, these authors further reported the B(C 6 F 5 ) 3 -catalysed reductive carbocyclisation of homoallylic alcohols and dihydro-2H-pyrans with Me 2 EtSiH or PhSiH 3 as reductants to construct a range of 1,2-disubstituted (hetero)arylcyclobutanes under mild reaction conditions with high efficiency and excellent cis-selectivity. 54 Mechanistic studies suggested a stepwise, dual ring-closing pathway (not shown).…”