Expanding the Scope of Arylsulfonylacetylenes as Alkynylating Reagents and Mechanistic Insights in the Formation of Csp²Csp and Csp³Csp Bonds from Organolithiums

Abstract

We describe the unexpected behavior of the arylsulfonylacetylenes, which suffer an "anti-Michael" addition of organolithiums producing their alkynylation under very mild conditions. The broad scope, excellent yields, and simplicity of the experimental procedure are the main features of this methodology. A rational explanation of all these results can be achieved by theoretical calculations, which suggest that the association of the organolithiums to the electrophile is a previous step of their intramolecular attack and is responsible for the unexpected "anti-Michael" reactions observed for substituted sulfonylacetylenes.

Strongly Luminous Tetranuclear Gold(I) Complexes Supported by Tetraphosphine Ligands, meso‐ or rac‐Bis[(diphenylphosphinomethyl)phenylphosphino]methane

“…Instead of the expected Michael products, they observed the exclusive formation of the products of alkynylation at the benzylic position44 (see below). Once this behavior had been identified as typical of Truce's reaction and its unexplored large synthetic potential as an alkynylation procedure had been realized, the authors initiated a systematic study to establish the scope and limitations of the method 45,46…”

“…). The reaction between phenyl‐( p ‐tolylsulfonyl)acetylene and n BuLi (both commercially available) in THF afforded, in less than 5 min at –78 °C, 1‐phenylhex‐1‐yne in excellent yield (Scheme ) 45. The Michael addition product was not detected.…”

“…The method was also used for the synthesis of 1,2‐dialkyl acetylenes through reactions between alkyl 2‐( p ‐tolylsulfonyl)acetylenes and tertiary, secondary, or primary alkyllithiums 45. Reactions of tert ‐butyl acetylenes occurred in almost quantitative yields (bottom, Scheme ).…”

“… Formation of Csp 2 –Csp bonds through reactions between aryllithium reagents and 2‐substituted ( p ‐tolylsulfonyl)acetylenes 45…”

Computational Perspectives on Organolithiums

“…The competing reactions were modeled by TS calculations at the B3LYP level of theory and included also a systematic variation in both R and R ′ groups. A rational explanation of their results was presented [140]. DFT calculations and in situ IR studies also helped Clayden and coworkers [141] illuminate the reaction mechanism for vinylation migration reactions, generating functionalized quarternary stereogenic carbon centers.…”