The thermal C²–C⁶ (Schmittel)/ene cyclization of enyne–allenes – crossing the boundary between classical and nonstatistical kinetics

Abstract

The thermal C 2 -C 6 /ene cyclization of enyne-allenes has become an exciting venue for both mechanistic and synthetic studies. While at first most efforts were aimed at establishing the diradical nature of the thermal process and to derive therefrom efficient protocols for synthetic schemes, recent evidence has disclosed the C 2 -C 6 cyclization as a unique reaction heavily influenced by nonstatistical dynamic effects. Depending on the substituents at the enyne-allene, one can readily identify transitions between classical and nonstatistical behaviors on the basis of experimental data. We are grateful to him for his friendship and many scientific enlightenments.a M. Schmittel, C. Vavilala, M. E. Cinar FB 8 (

Double Transfer of Chirality in Organocopper‐Mediated bis(Alkylating) Cycloisomerization of Enediynes

“…The most common method used to access these frameworks is the condensation of cyclopentadienes onto carbonyl groups. [15] Other strategies, based on the above-cited Schmittel cyclization of hindered enediynes [16,17] or more recent metal-catalyzed procedures, have been developed. [18] No example of chiral fulvene formation through a cycloisomerization reaction has been reported to date.…”

α,n‐Didehydrotoluenes by Photoactivation of (Chlorobenzyl)trimethylsilanes: An Alternative to Enyne–Allenes Cyclization

“…Received: April 11, 2012 Revised: June 8, 2012 Published online: July 13,2012 . Keywords: arenes · photochemistry · radicals · silanes · synthetic methods…”

“…In ethanol the reaction was slower than in methanol and led to an analogous product mixture (6, 7 b, 8 b, 9; entry 4). The other products result from the loss of the SiMe 3 group as well as that of chlorine, that is, via 13. In contrast, in the presence of allyltrimethylsilane (ATMS) some of the allylated 5 was formed, [19a] the yield of which increased with an increase in the ATMS concentration (entries 6 and 7).…”

Enediynes, enyne‐allenes, their reactions, and beyond

“…Enyne‐allenes can perform the Myers–Saito cyclization leading to the α‐3‐didehydrotoluene biradical whereas the corresponding Schmittel cyclization generates the fulvene biradical . There have been several reviews, which summarize the experimental investigations of these reactions, and therefore only some of the highlights in the research on enediyne reactions are pointed out here, especially those, which turned out to provide reference data for the quantum chemical investigations on enediynes and their rearrangement products.…”

“… Thermodynamics and kinetics : Wenthold provided an overview of all experimental thermochemical properties of benzynes up to 2010 . An earlier summary of benzyne chemistry complemented by a historic overview of their discovery and their applications in synthesis was given by Wentrup, Recently, Schmittel et al addressed the kinetics of the reaction bearing his name Vibrational spectroscopy : In 1998, Sander reviewed the vibrational spectroscopy of m ‐ and p ‐benzyne …”