Enantioselective syntheses of a 1α-hydroxyvitamin D ring A precursor from 3-(triphenylsilyl)glycidol and from malic acid

1,n-Dicarbanionic Titanium Intermediates from Monocarbanionic Organometallics and Their Application in Organic Synthesis

“…This cyclopropanol formation also proceeds smoothly with alkenyl-, cycloalkyl-, − , and arylcarboxylates 177,179 as well as with carboxylates containing β- 186,195 or γ-halogen, acetal, , and quite a number of other functional substituents including dialkoxyphosphonyl groups (see Table ). This methodology offers the best way to prepare the key precursors to bicyclopropylidene ( 48 ) 180,181 and its bisspirocyclopropanated analogue 49 , since methyl cyclopropanecarboxylate and ethyl dispiro[2.0.2.1]heptane-7-carboxylate are virtually quantitatively converted to 1-cyclopropylcyclopropanol and 1-(dispiro[2.0.2.1]hept-7-yl)cyclopropanol (Scheme ) .…”

Synthetic Applications of Intermolecular Cyclopropanation of Carboxylic Esters with Dialkoxytitanacyclopropane Reagents

“…[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 . Ester 70, readily accessible from -(ϩ)-malic acid (69), was converted into cyclopropanol derivative 71 in high yield by treatment with titanacyclopropane reagent 1.…”

The Kulinkovich hydroxycyclopropanation reaction in natural product synthesis

“…Therefore, various analogues that differ in the substitution of the A-ring or vary in the side chain are being developed to increase potency and selectivity. Wicha et al 25 The key intermediate in the synthesis was conjugated nitroalkane 14 which was synthesised from dibromoketone 13. Dibromoketone 13 was furnished via Kulinkovich cyclopropanation of ethyl 3-bromopropionate 11 followed by ring cleavage of cyclopropanol 12.…”