Gold-Catalyzed Cycloisomerization of 1,6-Diyne Carbonates and Esters to 2,4a-Dihydro-1H-fluorenes
摘要:
A synthetic method to prepare 2,4a-dihydro-1H-fluorenes efficiently from gold(I)-catalyzed 1,2-acyloxy migration/cyclopropenation/Nazarov cyclization of 1,6-diyne carbonates and esters is described. The suggested reaction pathway provides rare examples of [2,3]-sigmatropic rearrangement in this class of compounds as well as the involvement of an in situ formed cyclopropene intermediate in gold catalysis. Experimental and ONIOM(QM:QM') [our own n-layered integrated molecular orbital and molecular mechanics(quantum mechanics quantum mechanics')] computational studies based on the proposed Au carbenoid species provide insight into this unique selectivity.
Here we report the first example of alkyne trifunctionalization through simultaneous construction of C–C, C–O, and C–N bonds via goldcatalysis. With the assistance of a γ-keto directing group, sequential gold-catalyzed alkynehydration, vinyl–gold nucleophilic addition, and gold(III) reductive elimination were achieved in one pot. Diazonium salts were identified as both electrophiles (N source) and
Gold-catalyzed cycloisomerization of alk-4-yn-1-ones
作者:Volker Belting、Norbert Krause
DOI:10.1039/b819704k
日期:——
Depending on the substitution pattern and the solvent, the gold-catalyzed cyclization of alk-4-yn-1-ones 1 affords different oxygen heterocycles under mild reaction conditions. Alkynones with one substituent at C-3 undergo a 5-exo-dig cycloisomerization to substituted furans 2, whereas a 6-endo-digcyclization to 4H-pyrans 3 is observed with substrates bearing two substituents at C-3. In alcoholic solvents