Bei der Umsetzung von Triphenyl‐phosphin‐methylen und seinen in der Methylengruppe substituierten Derivaten mit Aldehyden und Ketonen wird der doppelt gebundene Sauerstoff gegen die Methylenreste ausgetauscht, wobei Triphenyl‐phosphinoxyd und die entsprechenden ungesättigten Verbindungen entstehen. Der mit dieser neuen Methode sich abzeichnende präparative Fortschritt liegt darin, daβ die C=C–Bindung ohne Verschiebung am Ort der ursprünglichen C=O–Bindung ausgebildet wird.

(R)‐Amino Acids can be synthesized via the cyclic bislactim ethers (dihydropyrazines) of cyclo‐(L‐Val‐Gly), by successive metalation, alkylation, and hydrolysis, in good yields and in high optical purity. They are e.g. of importance as enzyme inhibitors. Presumably the reaction proceeds via the planar dihydropyrazine anion (1).

No abstract

The Wittig rearrangement of ethers metalated in the alpha position with alkali metals is a I,2-shift to an atom with a lone pair of electrons. The alkyl shift proceeds with racemization (and partial retention) at the migrating carbon atom. The experimental observations suggest a cleavage-recombination mechanism involving a radical pair, as must also be assumed for the ylide rearrangements. In the ally1 migration, the double bond is displaced within the migrating residue (allyl inversion). This is readily explained by a one-step SNi' mechanism, the transition state of which is allowed on symmetry grounds, In the case of benzyl2-butynyl ether metalated on the butynyl residue, the ortho isomerization (corresponding to the Sommelet rearrangement) predominates.a-Metalated alkyl isocyanides can react with carbonyl compounds to form olefins and metal cyanate (carbonyl olefination). Isocyanoacetic esters occupy a special place; they react with aldehydes and ketones to form p-substituted a-formylaminoacrylates (formylaminoalkoxycarbonylmethylenation), which can enter into a wide range of reactions. p-Hydroxyalkyl isocyanides or 2-oxazolines can be isolated as intermediates in the carbonyl olefination. a-Metalated isocyanides react with acylating agents to form p-ketoalkyl isocyanides, which cyclize to give oxazoles.Like all branches of our science, carbanion chemistry is currently in a state of rapid development 11-41. The present article cannot, therefore, be a review, but can merely point out individual facets of research in this field.

Being both nucleophilic and electrophilic, a-metalated isocyanides can add to polar double bonds, forming heterocycles. They are also synthons for a-metalated primary amines. This article describes recent or improved procedures for their use in organic synthesis: 1) In heterocyclic syntheses to give 2-oxazolines, 2-imidazolines, 2-thiazolines, oxazoles and oligooxazoles, thiazoles, triazoles, imidazolinones, pyrroles, 5,6-dihydro-1,3-oxazines and -thiazines, and (via cycloaddition with nitrones) 2-imidazolidinones. 2) In the field of formylaminomethylenation, for example transformation of estrone methyl ether and a keto sugar into the corresponding a-formylaminoacrylic esters, and the conversion of aldehydes and ketones by 3-and 4-pyridylmethyl isocyanides into N-( I-pyridyl-1-a1kenyl)formamides and their hydrolysis to 3-and 4-acylpyridines. 3) In connection with the use of a-metalated isocyanides as synthons for a-metalated primary amines, the author demonstrates how they may be used for preparation of 1,2-and 1,3-amino alcohols, 1,2-diamines, 2,3-diaminoalkanoic acids and for synthesis of higher amino acids starting from simple amino acids.