Rhodium‐Catalyzed Intramolecular [5+2] Cycloaddition of Inverted 3‐Acyloxy‐1,4‐enyne and Alkyne: Experimental and Theoretical Studies

Abstract

By switching the position of the alkene and alkyne, a new type of 3-acyloxy-1,4-enyne (ACE) five-carbon building block was developed for Rh-catalyzed intramolecular [5+2] cycloaddition. An electron-withdrawing acyl group on the alkyne termini of the ACE was essential for a regioselective 1,2-acyloxy migration. This new method provided bicyclic [5.3.0]decatrienes that are different from previous methods because of the positions of the alkenes and the acyloxy group. Multiple mechanistic pathways become possible for this new [5+2] cycloaddition and they are investigated by computational studies.

Calculation of Reaction Free Energies in Solution: A Comparison of Current Approaches

“…To solve this problem the authors suggested setting all frequencies below 100 cm –1 to exactly this value so that their contribution to the entropy is not overestimated . This strategy was applied in the study of a rhodium-catalyzed cycloaddition by Li et al The authors found equal results for the rate limiting step of the reaction when applying or not this correction, and differences from 0 to 4 kcal mol –1 along the free energy profile. A slightly more sophisticated approach achieving similar results was also reported by Grimme; see Supporting Information.…”

“…In particular, calculation of the translational entropy in solution based on the particle-in-a-box model has been questioned. Several approaches have appeared in the literature to address this contribution, − several authors have commented on their use − and many researchers have applied these modified corrections in their investigations. − It has been argued that the translational entropy should not be estimated via the particle-in-a-box model for a system in solution. Translational and rotational entropies have been proposed to change significantly in solution as the solvent somehow restricts the movements of the solute with respect to what happens in gas phase. ,,, Some authors have estimated that the total entropy in solution should be about 50–70% of that in the gas phase, − and different proposals have been put forward to estimate the translational component of the entropy by recomputing or applying a correction to Δ S 0 trans .…”

Tandem Reactions of Ynones: via Conjugate Addition of Nitrogen‐, Carbon‐, Oxygen‐, Boron‐, Silicon‐, Phosphorus‐, and Sulfur‐Containing Nucleophiles

“…There are only few report on the cyclizations of ynone esters,– presumably due to the lack of a suitable flexible carbon chain. As in previous studies, intramolecular cycloaddition/rearrangement and cycloaddition/elimination sequences of 2‐methylprop‐1‐ene (or EtOAc) were the most commonly used pathways. As an example of pathway B, the Fürstner group achieved the synthesis of 4‐hydroxy‐2‐pyrones 97.4 based on a gold‐catalyzed cycloaddition/elimination of 2‐methylprop‐1‐ene [Eq.…”

Recent Developments in the [5+2] Cycloaddition

“…Indeed, a new type of 3-acyloxy-1,4-enyne five-carbon building block was developed by the same authors for rhodium-catalyzed intramolecular [5+2] cycloadditions. [80] When these inverted 3-acyloxy-6-keto-1,4-enyne substrates 114 were submitted to 5 mol% of [Rh(cod) 2 ] + BF 4…”