Homologation, ester

ETHYL 1 -NAPHTHYLACETATE ESTER HOMOLOGATION VIA YNOLATE ANIONS... 

Rajarathnam E. Reddy and Conrad J. Kowalski 146 ETHYL 1 -NAPHTHYLACETATE ESTER HOMOLOGATION VIA YNOLATE ANIONS... 

To achieve, then, high acetic acid selectivity directly from synthesis gas (eq. 1) it is necessary to balance the rates of the two consecutive steps of this preparation - ruthenium-carbonyl catalyzed methanol formation (10) (Figures 2 and 5) and cobalt-carbonyl catalyzed carbonylation to acetic acid (Figure 6) - such that the instantaneous concentration of methanol does not build to the level where competing secondary reactions, particularly methanol homologation (7, H), ester homologation (12, 13), and acid esterification (1 ), become important. 

Table IV shows that ester homologation is not limited to methyl...

Possible applications of ester-homologation reactions. The coproduction of acetic acid and ethyl acetate according to Reaction 4 may find some interesting applications ... 

Formic esters homologation - Ruthenium catalysts based on [Ru(00)3X3] species are sole Group VXIX metal systems able to hydrogenate and homologate the formyl group of formic esters to methyl and acetyl derivatives without causing an extensive decarbonylation of the formyl moiety (eqs.7,8) (17). 

The Kowalski Ester Homologation provides a similar conversion (C. Kowalski, M. S. Haque, Journal of Organic Chemistry 1985, 50, 5140)... 

Ester homologation (11, 104).2 In an improved method for ester homologation via an a-bromo-a-keto dianion, an ester (RCO Hs) is treated sequentially with LiCHBr2, LiTMP (1 equiv.), and then an excess of BuLi to provide RC=C—OLi. Rearrangement occurs with complete retention of stereochemistry. This method provides a stereospecific synthesis of the antibiotic oudemansin (2). 

A further reaction of the above type is ester homologation. The production of ethyl acetate from methyl acetate (equation 71) using similar catalytic systems to the above has been studied.382... 

Reaction of boronic esters, RB(OR )2, with dichloromethyllithium, LiCHCl2, inserts the CHC1 unit into the carbon-boron bond of the boronic ester. This is known as boronic ester homologation. If boronic esters derived from homochiral alcohols are used in this reaction, then new homochiral centres may be generated as will be illustrated below. 

Many boronic ester homologation reactions have been performed using pinanediols as chiral auxiliaries. These are readily available from (+)- and (-)-a-pinene by osmium tetroxide-catalyzed oxidation reactions (Equations B6.1 and B6.2). 

Boronic ester homologation has been used to synthesize specifically deuterated phenylalanine by the pathway shown in Figure B6.3. 

Recently, Matteson and his co-workers have demonstrated interesting boronic ester homologation with very high chiral selectivity and its use in syntheses of natural products 220 . 

Boronic ester homologation. (R,R)-2,3-Butanediol- and (-(- )-pinanediol have been used as the chiral adjuncts in a diastereoselective homologation of dichloromethaneboronic esters (1) to the (aS)-a-chloroboronic esters (2). Reaction of 1 with an alkyllithium produces a borate complex (a), which rearranges diastereoselectively in the presence of ZnCl, to 2 with introduction of a chiral center adjacent to boron. The reaction permits... 

Ester homologation. The anion of 1 reacts with carbonyl compounds to form kctenc-O.S-acctals (2), which are converted into homologated methyl esters (3) by reaction with methanol in the presence of HgCh. 

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