Esters from organometallic compounds

We need carbonyl groups to do conjugate addition so the tertiary alcohols will have to be made from them. In Chapter 9 (p. 222) we saw how to make such tertiary alcohols from esters and organometallic compounds and in Problem 1 of this set we saw how to do double conjugate additions on unsaturated esters - all the pieces fit together. 

Organometallic compounds or carbanions undergo a number of reactions in which the carbanion or carbanion-like moiety of the organometallic compound acts as a nucleophilic displacing agent. Examples are the formation of hydrocarbons from alkyl halides, alkyl halides from halogens, and ketones from acid chlorides or esters. The latter two reactions are closely related to the base-catalyzed condensations and are perhaps additions as well as displacement reactions. Related addition reactions are the carbonation of organometallic compounds and the addition to ketones or aldehydes. 

Manufacture and Uses. Acetoacetic esters are generally made from diketene and the corresponding alcohol as a solvent in the presence of a catalyst. In the case of liquid alcohols, manufacturing is carried out by continuous reaction in a tubular reactor with carefully adjusted feeds of diketene, alcohol, and catalyst, or alcohol—catalyst blend followed by continuous purification (Fig. 3). For solid alcohols, an inert solvent is used. Catalysts used include strong acids, tertiary amines, salts such as sodium acetate [127-09-3], oiganophosphorus compounds, and organometallic compounds (5). 

These boronic esters are easily hydrolyzed to give /ra .v-alkenylboronic acids with complete retention of their stereochemistry (C in Figure 16.15). Alkenylboronic esters and alkenylboronic acids are organometallic compounds that can be alkenylated and arylated in Pd-catalyzed reactions (Section 16.4.2). Aside from this, the iraws-alkenylboronic acid esters as well as the /rau.v-alkenylboronic acids are valuable precursors of haloalkenes (Figure 16.15). 

In the Claisen condensation, we have just seen, carbanions are generated from esters through abstraction of an a-hydrogen by base. But we arc familiar with another way of generating carbanions—or rather, groups with considerable carbanion character through formation of organometallic compounds. This approach, too, plays a part in the chemistry of esters. 

O. R. 1-9, C. R. Hauser and B. E. Hudson, Jr., The Acctoacetic Ester Condensation and Related Reactions lV-4, S. M. McElvain, The Acyloins 11-4, W. S. Johnson, The Formation of Cyclic Ketones by Intramolecular Acylation VIII-2, D. A. Shirley, The Synthesis of Ketones from Acid Chlorides and Organometallic Compounds of Magnesium, Zinc, and Cadmium. ... 

In the Suzuki coupling37 the trialkyltin functional group on the nucleophilic partner in the coupling reaction is replaced by a boronic acid 234. These stable compounds are easily made from simple organometallic compounds and boronic esters 233 followed by hydrolysis. 

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