Unveiling the role of boroxines in metal-free carbon–carbon homologations using diazo compounds and boronic acids

Abstract

By means of computational and experimental mechanistic studies the fundamental role of boroxines in the reaction between diazo compounds and boronic acids was elucidated.

A Versatile Route to Unstable Diazo Compounds via Oxadiazolines and their Use in Aryl–Alkyl Cross‐Coupling Reactions

“…[*] Dr.A.Greb, [ Using an umber of oxadiazolines and readily available boronic acids (forming boroxines in situ), [13] we were able to demonstrate ar emarkably broad reaction scope and unusually high functional-group compatibility (Table 1). With respect to the oxadiazoline component, av ariety of pharmaceutically relevant 4-, 5-and 6-membered saturated heterocyclic examples were viable coupling partners,i ncluding pyran (3a), tetrahydrofuran (3b), tetrahydrothiopyran (3c), tetrahydrothiophene (3d), thietane (3e), N-Boc piperidine (3f), N-Boc pyrrolidine (3g), and N-Boc azetidine (3h)rings, providing moderate to excellent yields of the desired C(sp 2 )À C(sp 3 )c ross-coupling products.I ti sp articularly notable that the 4-membered rings were viable examples given the instability of 4-membered cyclic diazo compounds, [14] which arises from the relief of ring strain when moving from an sp 2 to an sp 3 carbon center on reaction with electrophiles.…”

A Versatile Route to Unstable Diazo Compounds via Oxadiazolines and their Use in Aryl–Alkyl Cross‐Coupling Reactions

“…Using a number of oxadiazolines and readily available boronic acids (forming boroxines in situ), we were able to demonstrate a remarkably broad reaction scope and unusually high functional‐group compatibility (Table ). With respect to the oxadiazoline component, a variety of pharmaceutically relevant 4‐, 5‐ and 6‐membered saturated heterocyclic examples were viable coupling partners, including pyran ( 3 a ), tetrahydrofuran ( 3 b ), tetrahydrothiopyran ( 3 c ), tetrahydrothiophene ( 3 d ), thietane ( 3 e ), N ‐Boc piperidine ( 3 f ), N ‐Boc pyrrolidine ( 3 g ), and N ‐Boc azetidine ( 3 h ) rings, providing moderate to excellent yields of the desired C(sp 2 )−C(sp 3 ) cross‐coupling products.…”

Room Temperature Coupling of Aryldiazoacetates with Boronic Acids Enhanced by Blue Light Irradiation

“…Previous metal‐free methods reported for the alkylation/arylation of aryldiazoacetates are based on thermal reactions ( T >100 °C) of hydrazones with boronic acids, or reacting α‐ diazocarbonyl compounds or TMSCHN 2 with boroxines. Metal‐catalyzed approaches using boron derivatives and diazo compounds have been also performed at lower temperatures by using Rh, Cu and Pd…”