A highly flexible and concise total synthesis of (+)-podophyllotoxin featured with an enantioselective sequential conjugate addition-allylation reaction was reported. Starting from commercially available 3,4,5-trimethoxycinnamic acid, this new route leads to (+)-podophyllotoxin 1 in only eight steps with 29% overall yield.
A series of 1,2- and 2,3-fused quinazolinones have been synthesized in good to excellent yields through gold-catalyzed selective hydroarylations of alkynyl quinazolinone-tethered pyrroles. The studies revealed that 1,2-fused quinazolinones were obtained through a 1,3-rearrangement and sequential 6- exo-trig cyclization of N1-alkynyl quinazolinone-tethered pyrroles, while N3-alkynyl quinazolinone-tethered pyrroles went through 6- exo-dig or 7- endo-dig cyclizations directly to afford 2,3-fused quinazolinones. The fused quinazolinones could be prepared at gram scale in three steps from commercial ortho-aminobenzamide.
Diverse functionalized quinoxalines were synthesized in good yields from arylamines and readily available β-keto oximes through condensation and metal-free N-arylation. The reaction was compatible with various functional groups, such as halides, cyano, and esters. A mechanism was proposed based on the experimental results. These quinoxalines were easily obtained on a gram scale and converted to various useful scaffolds. Compound LASSBio-1022 was prepared in 83% yield in two steps.
An efficient method to synthesize rutaecarpine derivatives via the gold-catalyzed selective cyclization of alkyn-tethered indoles under mild conditions is described. The alkyn-tethered indole can undergo 6-exo-dig cyclization by oxidation and sequential gold catalysis, while it goes through 7-endo-dig cyclization by gold catalysis and sequential oxidation. Substrate scope studies reveal that the selectivity of cyclization was controlled by the substrates with sp and sp hybridization of carbon at the 2 position in quinazolinone. Furthermore, the rutaecarpine scaffold was prepared in 67% yield at gram scale easily in four steps from isatoic anhydride.
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