Cyclopropanol chemistry

Synthetic Applications of Intermolecular Cyclopropanation of Carboxylic Esters with Dialkoxytitanacyclopropane Reagents

“…[8,13] Although the titanacyclopropane reagent 1 acts as the ethyl anion equivalent, in the two-step sequence of titanium-mediated cyclopropanation of esters followed by isomerization of the forming cyclopropanols, this transformation has good preparative value because it represents, to the best of our knowledge, the most convenient way to convert carboxylic esters into ethyl ketones (Scheme 22).…”

“…[61] Scheme 22 Scheme 23 Base-induced heterolytic ring cleavage of 1,2-disubstituted cyclopropanols usually proceeds in a highly regioselective manner to generate the most stable carbanionic intermediate, which leads to linear or methyl branched ketones depending on the carbanion stabilizing properties of the substituent at the C2 carbon atom (Scheme 24). [8,13] Scheme 24…”

“…[8,13] For example, the titanium-mediated cyclopropanation of ethyl 4-chlorobutyrate (62) with reagent 1 led to the cyclopropanol 63, which was easily converted into 1-bromo-6-chlorohexa-3-one (64) by reaction with bromine in aqueous 2-propanol. [63] Dihalo ketone 64 was transformed to pyrazole alkaloid withasomnine (65) Wicha and co-workers [64] used the transformation of carboxylic esters into vinyl ketones via the corresponding cyclopropanols for the preparation of chiral anti-diol 68, one of the key intermediates in the synthesis of 11α-hydroxyvitamin D 3 .…”

“…Oxidation of cyclopropanols with various metal salts, as well as with nonmetal-based oxidants, proceeds by a radical mechanism. [8,13] As an example, treatment of 1-substituted and 1,2-disubstituted cyclopropanols with molecular oxygen in the presence of Mn() abietate or manganese() acetylacetonate leads to the formation of peroxides 92 as a result of the trapping of gaseous oxygen by the intermediate β-oxoalkyl radicals 93. [72] In the case of 1,2-disubstituted cyclopropanols, the cleavage of the most substituted Scheme 32 carbonϪcarbon bond was observed to occur with high regioselectivity.…”

Bis alkoxytitanacyclopropanes and -propenes (Kulinkovich reagents): Versatile reagents for carbon—carbon bond formation

“…Hence, the ethyl group of the Grignard reagent has served as a synthetic equivalent of a two-carbon dianion synthon 3 -a quite unusual reactivity pattern (Scheme 1). Additionally, the reaction products -the cyclopropanols 2 -are of considerable interest since they are not only valuable synthetic intermediates which allow for facile, selective ring-opening reactions [2] but which may be used as building blocks for the construction of cyclopropane containing natural products [3].…”