Metal-free borylative ring-opening of vinyl epoxides and aziridines

Abstract

A rational approach towards the borylative ring-opening of vinylepoxides and vinylaziridines, by the in situ formed MeO(-)→bis(pinacolato)diboron adduct, has been developed. The enhanced nucleophilic character of the Bpin (sp(2)) moiety from the reagent favours the SN2' conjugated B addition with the concomitant opening of the epoxide and aziridine rings. The reaction proceeds with total chemoselectivity towards the polyfunctionalised (-OH or -NHTs) allyl boronate. Theoretical calculations have determined the transition states that come from the reaction of the vinylic substrates with the activated MeO(-)→bis(pinacolato)diboron adduct, and a plausible mechanism for the organocatalytic borylative ring opening reaction has been suggested.

Quantitative Structure–Activity Relationships for the Nucleophilicity of Trivalent Boron Compounds

“…[4,17,18] The quaternization of one boron by the base polarizes the BÀBb ond inducing nucleophilic character on the sp 2 boron. [7] Here, we considered adducts derived from intermolecular alkoxide activation of symmetric bis(pinacolato)diboron (Bpin 2 , 5) [7,19] and unsymmetrical diboron Bpin-Bdan (dan = 1,8-diaminonaphthalene, 6), [20] as well as the intramolecular activationb yt he nitrogen atom in the pinacolato diisopropanolaminato diboron 7. [21] Moving to boryl-transition-metal complexes, we noted that their reactivity switchesd epending on the nature of the transition metal.…”

Selective C−C Coupling of Vinyl Epoxides with Diborylmethide Lithium Salts

“…The in situ oxidation of the homoallylboronates prepared in Table allows for the isolation of challenging bishomoallylic alicyclic 1,3‐diols (Scheme ) in a straightforward manner. Interestingly compounds 33 , 35 , and 37 have a complementary conformation to the previously reported method through Ni or transition‐metal‐free catalyzed S N 2′ borylation/ring opening of vinyl epoxides with B 2 pin 2 …”

Transition‐Metal‐Free Heterobiaryl Synthesis via Aryne Coupling

“…Under these conditions, the reaction led exclusively to the addition product of diisopropylamine (DIA) on benzyne demonstrating the much higher reactivity of lithium amides in comparison to that of the generated lithiated pyridine [2f-h-Li]. Although the reaction of primary and secondary amines with arynes has been well established, [50,51] addition of tertiary amines to arynes is only scarcely described in the literature, [52][53][54] and was far less expected with regard to the concomitant presence of the lithiated species.…”