Regioselective and Stepwise [8 + 2] Cycloaddition Reaction between Alkynyl–Fischer Carbene Complexes and Tropothione

Abstract

The formal [8 + 2] cycloaddition reaction between alkynyl Fischer carbene complexes and tropothione leads to the regioselective formation of novel 3aH-cyclohepta[b]thiophene carbene complexes. Computational DFT calculations indicate that the process proceeds stepwise via antiaromatic zwitterionic intermediates.

Higher-order cyclization reactions of alkenyl Fischer carbene complexes: a new selective all-carbon [8 + 2] cyclization with 8-methoxyheptafulvene and computational mechanistic analysis

“…We started the theoretical study by modelling the reaction between carbene complex 1e (R 1 =2-furyl) and 8methoxyheptafulvene 2. This large asymmetry is in agreement with previously computed cycloadditions 9,13,15 and it should be attributed to the electron-donating effect of the methoxy group on heptafulvene 2 together with the electronwithdrawing effect of the conjugated C=Cr bond on the carbene complex 1e. For this reaction, two different reaction pathways, concerted versus stepwise, are possible.…”

“…Similar level of theory demonstrated to be useful in the elucidation of reaction mechanisms of cycloaddition reactions 9,13 and organometallic compounds involving reactions. Similar level of theory demonstrated to be useful in the elucidation of reaction mechanisms of cycloaddition reactions 9,13 and organometallic compounds involving reactions.…”

Recent Developments on the Synthesis of Various Sulfur‐Containing Heterocycles via [3+2]‐ and [4+2]‐Cycloaddition Reactions with Thiocarbonyls

“…Another unusual higher cycloaddition chemistry (i. e., a formal [8 + 2]) of tropothione and alkynyl-Fischer carbene complex is recently disclosed by Sierra and co-workers (Scheme 29). [48] This regioselective transformation was found to proceed via a stepwise-fashion as corroborated through DFT-calculations. This cycloaddition afforded good to moderate yields of the final products, however, the substrate scope demonstrated in the study was limited.…”

Computational Chemistry; A Useful Tool for the Chemical Synthesis of Complex Molecules, Heterocycles and Catalysts

“…23,24 In We also explored the formal [8+2] cycloaddition between alkynyl Fischer carbene complexes 24 and tropothione 25 to yield 3aH-cyclohepta[b]thiophene carbene complexes 26 (Scheme 11). 47 Also in this case, conceptual DFT studies revealed that the concerted [π8s+π2a] process was much higher in energy than the stepwise mechanism involving zwitterionic intermediate INT7. Therefore, the reaction proceeds through the stepwise pathway, leading to the final cycloadduct 26.…”