Abstract
We report a simple and straightforward route to hetero-functionalized cyclopropanes by addition of heteroatom nucleophiles to ethyl 2-(diethoxymethyl)cycloprop-2-ene-1-carboxylate. The resulting donor-acceptor substituted cyclopropane are useful synthetic intermediates owing to their high functionalization. Particular emphasis is placed in the stereochemical outcome of this reaction.
Highlights
Cyclopropenation of alkynes by diazocarbonyl compounds, promoted by copper or rhodium (II) catalysts, has been extensively studied.[1]
Owing to the absence of direct cyclopropanation methods for such hetero-substituted cyclopropanes,[6] we anticipated that these compounds could be prepared by reaction of ethyl 2-(diethoxymethyl)cycloprop-2ene-1-carboxylate (1) with different heteroatom nucleophiles
With the cyclopropene 1 in hand we have examined the addition of heteroatom nucleophiles (Table 1)
Summary
Cyclopropenation of alkynes by diazocarbonyl compounds, promoted by copper or rhodium (II) catalysts, has been extensively studied.[1]. Cyclopropenyl esters are very useful synthetic intermediates, readily available by slow addition of alkyl diazoacetates to an excess of the appropriate alkyne in the presence of a catalytic amount of rhodium acetate.[2] Following this general procedure, ethyl 2(diethoxymethyl)cycloprop-2-ene-1-carboxylate (1) was prepared in 72% yield by reaction of propionaldehyde diethyl acetal (2) with ethyl diazoacetate (Scheme 2), using dirhodium(II) tetraacetate as catalyst. The reaction of ethyl 2-mercaptoacetate (entry 3) with cyclopropene 1 using sodium hydride as base (1.1 equiv.) provided the cyclopropane 3c only in 25% yield.
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