Brønsted acid−catalyzed synthesis of tetrasubstituted allenes and polysubstituted 2H-chromenes from tertiary propargylic alcohols

Abstract

acid−catalyzed synthesis of tetrasubstituted allenes and polysubstituted 2H-chromenes from tertiary propargylic alcohols, Tetrahedron (2019), doi:

Chemoselective and Regioselective Synthesis of Spiroisoindolinone Indenes via an Intercepted Meyer–Schuster Rearrangement/Intramolecular Friedel–Crafts Alkylation Relay

“…When orcinol was submitted to the standard reaction conditions, spiroisoindolinone-derived 2 H -chromene 27 was isolated in 74% yield as a result of cyclization through hydroxy group. This type of heterocyclization was also observed in cascade reactions between tertiary propargylic alcohols and electron-rich phenols . Chromene derivative 28 was also obtained when sesamol was employed as an external nucleophile.…”

From Propargylic Alcohols to Substituted Thiochromenes: gem-Disubstituent Effect in Intramolecular Alkyne Iodo/hydroarylation

“…The generated tertiary propargyl cation intermediate, which could be more adequately represented as an allenium ion, evolves rapidly in different alternative reaction pathways from propargylic substitution, such as competitive elimination or S N ′ reactions forming allenes. 16 Moreover, thiols could react with propargylic alcohols through other different reactivity patterns that do not implicate a carbocation at the propargylic position, like hydrothiolation of alkynes. 17 Whereas thiolation of tertiary propargyl alcohols was efficiently accomplished using alkyl thiols, 15a , 15c , 15f with less nucleophilic thiophenols the reaction takes place with low yields.…”

“… 12 Remarkably, in two recent reports, few examples of S -aryl propargyl thioethers were efficiently synthesized from tertiary propargyl alcohols and an excess of thiophenol (2–3 equiv) by using catalytic amounts of a bimetallic Ir–Sn complex 18 or a lithium triflimidate salt. 19 To this end, and on the basis of our previous experience in the direct nucleophilic substitutions of propargylic alcohols, 15c , 16 , 20 we evaluated the propargylation of thiophenols employing p -toluenesulfonic acid monohydrate ( 1 , PTSA) as a promising, cheap, and easily accessible catalyst. After some optimization, 21 this simple Brønsted acid proved to be an efficient catalyst for accomplishing thiolation of a variety of tertiary propargylic alcohols 3 with different thiols 2 ( Scheme 3 ).…”

“…Although an acid catalyst can easily activate tertiary alcohols, the propargylic substitution reaction is more challenging. The generated tertiary propargyl cation intermediate, which could be more adequately represented as an allenium ion, evolves rapidly in different alternative reaction pathways from propargylic substitution, such as competitive elimination or S N ′ reactions forming allenes . Moreover, thiols could react with propargylic alcohols through other different reactivity patterns that do not implicate a carbocation at the propargylic position, like hydrothiolation of alkynes .…”

Cu-Catalyzed Synthesis of Tetrasubstituted 2,3-Allenols through Decarboxylative Silylation of Alkyne-Substituted Cyclic Carbonates

“…Allenes and their derivatives play an important role in organic synthesis constituting reactive intermediates en route to more complex structures and medicinally useful intermediates . The synthesis of allenes has rapidly advanced over the past decade, and various efficient protocols for tri- and tetrasubstituted scaffolds have been developed. Silylated congeners have been frequently targeted as these scaffolds can offer productive ways toward pharmaceutically relevant molecules and natural products if properly equipped with additional functionality.…”