Gold-Catalyzed Enantio- and Diastereoselective Syntheses of Left Fragments of Azadirachtin/Meliacarpin-Type Limonoids

Abstract

Meliacarpin-type limonoids are an important class of organic insecticides. Their syntheses are challenging due to their chemical complexity. Here, we report the highly enantio- and diastereoselective synthesis of the left fragments of azadirachtin I and 1-cinnamoylmelianolone, being two important family members of meliacarpin-type limonoids, via pairwise palladium- and gold-catalyzed cascade reactions. Gold-catalyzed reactions of 1,7-diynes were performed as model studies, and the efficient construction of tetracyclic late-stage intermediates was achieved on the basis of this key transformation. Our unique route gave both of the left fragments in 23 steps from the commercially available chiral starting material (-)-carvone. This study significantly advances research on the synthesis of the meliacarpin-type limonoids.

Asymmetric total synthesis of (1S,2S,4S)-β-elemene

“… 13 Therefore, our synthesis began with the preparation of optically pure intermediate 12 from the chiral pool building block ( R )-carvone 8 ($0.39 per g, Merck), as shown in Scheme 3 . Stimulated by Knölker's pioneering work, 14 a it was anticipated that the new generated stereogenic center in cyclohexanone 11 could be secured by diastereoselective 1,4-Michael addition of isopropenyl Grignard reagent 10 to 8. 14 b To our delight, we were able to isolate desired product 11 exclusively in 70% yield.…”

Gold(I)‐Catalyzed C−O/C−C Bond‐Forming Domino Reactions and Their Synthetic Applications

“…Another illustration of the synthetic utility of the domino reaction came in 2016, where the established method was used for the formation of the left fragment of azadirachtin‐type skeleton in a model study (Figure ) …”

Novel and rapid approach for benzanthrone synthesis: BBr3-promoted annulation of 8-aryl-1-naphthoic acid derivatives

“…However, multistep synthesis with transition-metal catalysis is often required to access such complicated skeletons. 1–10 In this study, we attempted the synthesis of a hydrogenated naphthalene furan skeleton by oxidative dearomatization strategy, as shown in Scheme 1(b). Firstly, BBr 3 was utilized to complete the C 5 -demethylation of methyl 5-methoxy-8-phenyl-1-naphthoate.…”