Ketoacetates synthesis

Soon it was found that good yields of many 1-azaquinolizinium salts could be obtained by adding either the ketoacetal (250) or a /3-chlorovinyl ketone (254) to an acidic solution of 2-aminopyridine (58DOK(l 18)297). This simple one-pot reaction was extended by the use of additional ketoacetals as well as j8-diketones (253) and malonaldehyde diacetal (Scheme 124). Table 14 illustrates the scope of this [3 + 3] addition mode of the 1-azaquinolizinium synthesis. 

Recently, a novel commercially available acetoacetoxyethyl metacry-late resin (37) is finding wide applications as a selective electrophilic scavenger resin. This resin has the ability to differentiate primary amines from a mixture where secondary amines are present.64,65 An illustrative example is depicted in the synthesis of dibenzylamine (38, Fig. 16) from benzaldehyde and benzylamine. Unreacted benzylamine is selectively removed from the reaction mixture upon treatment with the ketoacetate resin (37). 

The first report concerning the synthesis of 10-deaza-10-oxafolates described the preparation of 10-deaza-10-oxaFA (498) and 10-deaza-10oxaAP (499) by condensation of the ketoacetal (497) with the appropriate pyrimidine, followed by ester hydrolysis (Scheme 3.99) [51]. An improved, unambiguous synthesis [ 174] of (498) and (499) is outlined in Scheme 3.100 and is a modification of the Boon-Leigh procedure. Reaction of (500) with methyl p-hydroxy-... 

White peach scale. Several scale sex pheromones have now been elucidated each of them possesses an asymmetric center and usually a trisubstituted alkene link within an isoprenoid framework (43). The structure of the white peach scale pheromone, R,Zb-II (Figure 8), lent itself to synthesis with another chiral starting material, namely limonene (44). Selective ozonlysis followed by workup with dimethyl sulfide-methanol provided a ketoacetal, III. Wittig methylenation followed by hydrolytic cleavage of the acetal gave a dienaldehyde, IV. Conversion of the aldehyde via the acid to an amide (45) with enantiomerically pure ot-methylbenzylamine permitted chromatographic assessment of the purity of the diene aldehyde (and the limonene). The required R-isomer of the diene aldehyde was >48% ee. 

In 1973, it was demonstrated that 1,2-epoxystannanes, produced from vinylstannanes and MCPBA, could be isolated and characterized, in comparison widi 2,3-epoxystannanes (from allylstannanes), which are extremely reactive and have not been isolated (see Section 4.2.2.3). Subsequently, useful applications of 1,2-epoxy stannanes have been reported, including the internal alkyne ketone conversion, in the caibapenem and carbacephem 0-lactam antibiotic) skeletons. Ketone (10) should be of value in the construction of the biologically interesting l-carbapen-2-ene ring system. Synthesis of ketoacetates of potential use in the carbacephem system (e.g. 11 and 12) was also achieved by similar sequences shown in Scheme 11. ... 

The potential utility of the stereocontrol available through exo [6 + 4] cycloaddition in the tropone series can be seen in Garst s stereoselective cyclodecene synthesis. This methodology is predicate on the efficient translation of the double bond geometry from stereochemically homogeneous ( )- and (Z)-1-acetoxybutadiene via cycloadducts (30) and (35) into ( )-cyclodecene (36) and (Z)-cyclod ne (3, respectively. Reduction of cycloadducts (30) and (35) to the corresponding fiiUy saturated ketoacetates, followed by conversion to the mesylates and hydride reduction, led to the desired 10-membered ring products (36) and (37) in 78% and 40% yields, respectively. 

Ammonium ceric nitrate dissolved in 8 4 1 methanol/ethyl methyl ketone/isopropenyl acetate, after 20-25 min at room temp. aq. NaHC03 added, and the mixture heated at 40° for ca. 45 min with vigorous stirring -> product. Y 78%. The method is highly regiospecific. F.e., also synthesis of y-ketoacetals with addition of 2 C-atoms using vinyl acetate, and with dimethyl malonate in place of ketones, s. E. Baciocchi et al.. Tetrahedron Letters 28, 5357-60 (1987). 

As well as yielding a mixture of epimeric ketoacetates, in which the epimer required for the synthesis of lincosamine derivatives is a minor component, acetolysis of the diazoketone also gave the 3-oxetanone (112) (19% yield), a product of pyranose-ring opening. 

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