Michael W. Rathke

O-Silylation and Attempted O-Alkylation of Lithium Ester Enolates. The Synthesis of O-Silyl Ketene Acetals

Abstract The reaction of ketone enolates with alkylating or silylating reagents can be used to prepare O-alkyl or O-silyl vinyl ethers1. An analogous reaction of ester enolates would produce O-alkyl (I) or O-silyl (II) ketene acetals2. Such a simple route to ketene acetal structures would appear to be of major synthetic value3. Consequently, we have studied the reaction of lithium ester enolates, obtained from the corresponding esters and lithium N-isopropylcyclohexylamide (LiICA)4 as shown in eq. 1, with a variety of alkylating and silylating reagents.

The preparation and reactions of esters of dichloromethaneboronic acid

Abstract Dichloromethaneboronic acid is obtained in impure form from the reaction of dichloromethyllithium with trimethylborate. Reaction with the appropriate alcohols furnishes the 1,3 propandiol ester and the diisopropyl ester. Diisopropyldichloromethaneboronate reacts with organolithium or organomagnesium reagents to give substitution products which can be oxidized to aldehydes.

Synthesis of β-Keto Acids and Methyl Ketones Using Bis(trimethylsilyl) Malonate and Triethylamine in the Presence of Lithium or Magnesium Halides

Abstract Bis(trimethylsilyl) malonate is acylated in good yields with acid chlorides and acyl carbonates using triethylamine and magnesium or lithium salts to give β-keto acids or methyl ketones. Compared to other procedures, which use strong bases, this method is inexpensive, safe and convenient; especially for large scale reactions.

1.8 – Zinc Enolates: the Reformatsky and Blaise Reactions

The Reformatsky reaction is the reaction of an α-halo ester with an aldehyde or ketone in the presence of zinc metal as shown in Scheme 1. The usual product of the reaction is a (β-hydroxy ester, which may be dehydrated in subsequent steps to give an unsaturated ester. A zinc ester enolate (1), the so-called Reformatsky reagent, is an intermediate in the reaction and the sequence is thus classified as an aldol condensation. Compared to the usual base-promoted aldol procedures, the distinguishing features of the Reformatsky reaction are the use of a metal-halogen redox reaction rather than an acid-base reaction to form the enolate, and the fact that the counterion of the enolate is zinc.

Isolation and Reactions of the Lithium Di-enolate of Diethyl Succinate

Abstract The Stobbe condensation1 is a classical reaction of the mono-enolate, l, of diethyl succinate, generated in situ by action of alkoxide bases, with aldehydes or ketones (eq 1).

A convenient procedure for the preparation of reactive zinc for the Reformatsky Reaction

Abstract A reactive zinc powder is obtained by addition of ZnCl2 to a lithium dispersion suspended in ether. Reformatsky Reactions with the zinc powder are described.

Modified Wittig Reactions Using Triethylamine and Lithium Halides: Synthesis of α,β-Unsaturated Esters from Ketones and Ethyl Bis(Trifluoroethyl)Phosphonoacetate

Abstract A modified HWE reaction using triethylamine and lithium bromide with ethyl bis(trifluoroethyl)phosphonoacetate gives satisfactory yields of α,β-unsaturated esters from a variety of ketones.

The Alkylation of Ketone Enolates in the Presence of Triethanolamineborate. Control of Polyalkylation

Abstract The formation of polyalkylated products is a major source of difficulty in the alkylation of ketone enolates. To some extent, this difficulty can be minimized by the use of lithium rather than sodium or potassium enolates.3 We have observed that triethylboron serves as an effective additive to minimize polyalkylation.4 For example, treatment of a THF solution of the sodium enolate of cyclohexanone with one equivalent of methyl iodide produces major amounts of dimethylated ketones, while the same reaction conducted in the presence

Acylation of Trimethylsilyl Acetate. A Synthetic Route to β-Keto Acids and Methyl Ketones

Abstract β-Keto acids are important intermediates for the preparation of ketones1,2 and for the synthesis of a variety of natural products.3,4 These compounds have also been used extensively for studies of the mechanism of decarboxylation.5,6

A Convenient Procedure for Carboxylation—Robinson Annulations of Ketones Using Triethylamine Base in the Presence of Magnesium Chloride

Abstract Carboxylation of ketones with carbon dioxide in the presence of magnesium chloride and triethylamine followed by reaction with methyl vinyl ketone gives satisfactory yields of Michael and Robinson annulation products.