Expeditious Construction of the DEF Ring System of Thiersinine B

Abstract

Construction of a DEF ring model of thiersinine B has been achieved from a Wieland-Miescher ketone derivative by a five-step sequence featuring a one-pot regioselective α-allylation of the starting α,β-unsaturated ketone via the Claisen rearrangement and a double dihydroxylation of a dienone intermediate.

Unusual cyclic terpenoids with terminal pendant prenyl moieties: from occurrence to synthesis

“…150,[158][159][160][161][162][163][164][165][166][167] Some work on the synthesis of separate subunits belonging to different natural compounds have been also reported. [167][168][169][170]…”

Palladium-Catalyzed Oxidative Rearrangement of Tertiary Allylic Alcohols to Enones with Oxygen in Aqueous Solvent

“…The broad utility of β-disubstituted α,β-unsaturated ketones D (Figure ) in organic synthesis has continued to attract considerable synthetic efforts to develop more efficient methods for these ketones’ syntheses . The alkylative carbonyl transposition of β-disubstituted α,β-unsaturated carbonyl compounds (Figure ), which entails a 1,2-addition of A by organometallic reagents to form B , followed by isomerization of tertiary allylic alcohol B to C , and oxidation of C to the corresponding β-disubstituted α,β-unsaturated ketones D , represents a practical strategy that extends the synthetic latitude of this transformation.…”

An Unexpected 2,3-Dihydrofuran Derivative Ring Opening Initiated by Electrophilic Bromination: Scope and Mechanistic Study

“…Ring opening through C(4)–C(5) bond cleavage could yield intermediate D1 . Although classically the 2,3-dihydrofuran hemiacetal ring opening takes place at the C(5)–O bond, , we speculate that the presence of an electron-withdrawing Br group at the α-keto position might further stabilize the anion (i.e., the resonance intermediate D2 ) which might override the inherent ring opening preference. In the presence of only 1 equiv of NBS, intermediate D might be quenched by proton instead of the electrophilic Br to yield product 7 (Scheme , eq 3).…”

“…Typically, the enol ether moiety reacts with electrophiles to give the oxonium cationic intermediates followed by the attack of various nucleophiles to give the corresponding adducts, which can undergo ring opening to yield the alcohol derivatives (Scheme , eq 1). For example, water can be used as the nucleophile to give the lactol product, and this strategy has been applied in the synthesis of 4-ketoundecanoic acid. , In contrast, to the best of our knowledge there is no report on the cleavage of the C(4)–C(5) bond which led to the 2,3-dihydrofuran ring opening. Herein, we are pleased to report a novel ring opening reaction of 2,3-dihydrofuran derivatives to efficiently yield various linear chain keto-carboxylate products (Scheme , eq 2).…”