Fluoro‐Ene Reaction Versus [2+2] Cycloaddition in the Thermal C²–C⁶ Cyclization of Enyne‐Allenes: An Experimental and Theoretical Investigation

Abstract

A series of fluoroalkyl‐substituted enyne‐allenes have been synthesized by a new route with the aim of elucidating the possibility of a fluoro‐ene reaction via an intermediate fulvenyl diradical generated in the thermal C2–C6 (Schmittel) cyclization reaction. As a result of the strong C–F bond, fluorine atom transfer was not observed. Instead, 1H‐cyclobuta[a]indenes were formed in good yields despite the high strain energy. DFT calculations at the B3LYP level of theory indicated that although the fluoro‐ene reaction is the most exothermic reaction available, cyclobutene formation is kinetically favored over the [1,5]‐fluorine shift by 5–15 kcal mol–1 in various model compounds.

Nonstatistical Dynamics in the Thermal C2–C6/Diels–Alder Cyclization of Enyne-Allenes: Effect of Topology

“…Recently, we have developed a straightforward assay based on simple DFT computations and experimental results to estimate the amount of nonstatistical dynamics in the thermal C 2 –C 6 (Schmittel) , /Diels–Alder cyclization of enyne-allenes 1a – c (Scheme ) . With 1a – c exhibiting a similar directionality of the minimum energy path, that is, surface topology, we were able to validate the hypothesis of excess energy as a decisive factor controlling the amount of nonstatistical dynamics.…”

Brønsted Acid‐Promoted Benzannulation of o‐Alkynylbenzaldehyde and Alkyne, and the Positive Effect of Propargyl Alcohol

“…High‐resolution mass spectrometry (HRMS) data were recorded on a JMS‐700 quadrupole mass spectrometer. 2‐(Phenylethynyl)benzaldehyde 1 a – 1 c , [7b] 1 d , [27] 1 e , [7b] 1 f , [27] 1 g , [28] 1 h , [29] 1 i , [30] 1 j – 1 k , [7b] 1 l , [31] 3‐phenylprop‐2‐yn‐1‐ol ( 2 a ), [32] 2 b – 2 c , [33] 2 d , [34] 2 e – 2 h , [33] 2 i , [35] 2 j , [33] 2 k , [36] 1‐phenyl‐1‐propyne ( 7 ), [37] 8 , [38] 12 , [20] 13 [20] were prepared according to the literature procedure.…”

“…2-(Phenylethynyl)benzaldehyde 1 a-1 c, [7b] 1 d, [27] 1 e, [7b] 1 f, [27] 1 g, [28] 1 h, [29] 1 i, [30] 1 j-1 k, [7b] 1 l, [31] 3-phenylprop-2-yn-1-ol (2 a), [32] 2 b-2 c, [33] 2 d, [34] 2 e-2 h, [33] 2 i, [35] 2 j, [33] 2 k, [36] 1phenyl-1-propyne (7), [37] 8, [38] 12, [20] 13 [20] were prepared according to the literature procedure.…”