One-pot synthesis of γ-hydroxy-γ-oxaphosphonates using pentacovalent oxaphosphorane chemistry

P(V)-2,2,2-triethoxy-2,2-dihydro-5-methoxy-1,2λ⁵-oxaphospholene was synthesized as a new type of enolate which was hydrolyzed to give a series of phosphonates. In addition, aldol reaction of the oxaphospholene intermediate with several aldehydes as electrophiles under mild and neutral conditions produced phosphonate-containing aldol compounds through a two-step one-pot reaction.     

Stereoselective syntheses of substituted succinic acid derivatives of the iron chiral auxiliary [(η-C5H5)Fe(CO)(PPh3)]

A range of alkyl- or aryl-substituted iron succinoyl complexes, incorporating the iron chiral auxiliary [(η⁵-C₅H₅)Fe(CO)(PPh₃)], were prepared in high regio- and diastereoselectivities by employing four successful strategies: (i) the alkylation of chiral enolate equivalents with tert-butyl bromoacetate; (ii) the mutual kinetic resolution of tert-butyl α-bromoacetate with a chiral acetate enolate equivalent; (iii) the alkylation of chiral succinoyl enolate equivalents; (iv) the conjugate addition of organolithium reagents or lithium amide reagents to chiral fumaroyl derivatives. Oxidative cleavage of the iron chiral auxiliary was shown to occur without compromising the stereochemical integrity of the succinoyl fragments.     

Total synthesis of (−)-amathaspiramide F

The stereoselective total synthesis of the marine alkaloid, (−)-amathaspiramide F (1), was achieved from the α-hydroxy-α-ethynylsilane 2. The key steps involved in the synthesis were (1) the enolate Claisen rearrangement of the α-acyloxy-α-alkenylsilane for the stereoselective construction of the consecutive C5 and C9 chiral centers of 1 (erythro configuration), (2) the construction of aza-spirohemiaminal 28, and (3) dibromination during the final stage of the total synthesis. The reaction of the (Z)-α-acyloxy-α-alkenylsilane 22 possessing the Boc-homoallylglycine ester as the acyloxy group underwent stereoselective enolate Claisen rearrangement to give the desired erythro product 23. On the other hand, the reaction of the α-acyloxy-α-alkenylsilane (Z)-5 having Boc-proline gave the unexpected threo product 6. Oxidative cleavage of the vinylsilane group of 23 followed by treatment with heptamethyldisilazane as the methylamine equivalent gave aza-spirohemiaminal 28. The problematic regioselective dibromination to 28 was achieved using n-Bu₄NBrCl₂.     

Lithium Enolates: ‘Capricious’ Structures – Reliable Reagents for Synthesis

The first part of this review article deals with the structures of enolates. The development of research in this field during the last half century will be illustrated by highlightening seminal contributions, while, by no means, an attempt of comprehensiveness is made: the choice of spotlights has, admittedly, a personal touch. Aside from derivatization of lithium enolates and their crystal structures that meanwhile are classics, more recent solution studies are presented. In the second part, it will be shown by contributions of our laboratory that, despite their complicated structures, lithium enolates are reliable ‘workhorses’ in synthesis with emphasis being given to stereoselective C? C bond forming reactions due to the Pd‐catalyzed allylic alkylation of non‐stabilized, preformed enolates.