Asymmetric Cα-Alkylation of Proline via Chirality Transfers of Conformationally Restricted Proline Derivative: Application to the Total Synthesis of (-)-Amathaspiramide F

Recent asymmetric synthesis of natural products bearing an α-tertiary amine moiety via temporary chirality induction strategies

Covering: 2013 to 2023The α-tertiary amine moiety is a common structural motif in natural alkaloids and is frequently associated with intriguing biological activities and inherent synthetic challenges. A major hurdle in the total synthesis of these alkaloids is the asymmetric construction of the α-tertiary amine moiety. Temporary chirality inductions have been effective strategies employed to address this issue, particularly in natural product synthesis. The temporary chirality induction strategies in α-tertiary amine synthesis can be broadly classified into three categories based on the types of temporary chirality involved: Seebach's self-regeneration of stereocenters (SRS), C-to-N-to-C chirality transfer, and memory of chirality (MOC). This review highlights the recent advancements in temporary chirality induction strategies for the total synthesis of α-tertiary amine-containing natural products between 2013 and 2023.

Naturally Occurring Organohalogen Compounds-A Comprehensive Review

The present volume is the third in a trilogy that documents naturally occurring organohalogen compounds, bringing the total number-from fewer than 25 in 1968-to approximately 8000 compounds to date. Nearly all of these natural products contain chlorine or bromine, with a few containing iodine and, fewer still, fluorine. Produced by ubiquitous marine (algae, sponges, corals, bryozoa, nudibranchs, fungi, bacteria) and terrestrial organisms (plants, fungi, bacteria, insects, higher animals) and universal abiotic processes (volcanos, forest fires, geothermal events), organohalogens pervade the global ecosystem. Newly identified extraterrestrial sources are also documented. In addition to chemical structures, biological activity, biohalogenation, biodegradation, natural function, and future outlook are presented.

Total Synthesis of (-)-Amathaspiramide A via One-pot Aldol Addition/Transamidification Reaction

The total synthesis of (-)-amathaspiramide A was accomplished through an efficient construction of chiral aza-spirobicyclic core by aldol addition/transamidification cascade. The scope of the efficient construction methodology was investigated. Configuration...

Collective Asymmetric Total Synthesis of C-11 Oxygenated Cephalotaxus Alkaloids

While numerous studies pertaining to the total synthesis of Cephalotaxus alkaloids have been reported, only two strategies have been reported to date for the successful synthesis of the C-11 oxygenated subset, due to the additional synthetic challenge posed by the remote C-11 stereocenter. Herein, we report the collective asymmetric total synthesis of C-11 oxygenated Cephalotaxus alkaloids using a chiral proline both as a starting material and as the only chirality source. A tetracyclic advanced intermediate was synthesized in a highly stereoselective manner from l-proline in 8 steps involving sequential chirality transfer steps such as a diastereoselective N-alkylation, stereospecific Stevens rearrangement and intramolecular Friedel-Crafts reaction via an unusual O-acyloxocarbenium intermediate. From a common intermediate, the asymmetric total synthesis of six C-11 oxygenated Cephalotaxus alkaloids was completed by a series of oxidation state adjustments.

Asymmetric Synthesis of Cα-Substituted Prolines through Curtin-Hammett-Controlled Diastereoselective N-Alkylation

Asymmetric synthesis of α-substituted proline derivatives has been accomplished by an efficient chirality-transfer method. High diastereoselectivity of the N-alkylation of the proline ester (C→N chirality transfer) was achieved when a 2,3-disubstituted benzyl group was used as the N-substituent. DFT calculations provided a mechanistic rationale for the high degree of stereoselectivity. The generated N-chirality of the quaternary ammonium salt was transferred back to the α-carbon through a stereoselective [2,3]-Stevens rearrangement (N→C chirality transfer) to give α-substituted proline ester.