Diastereoselective Reduction of Cyclopropenylcarbinol:  New Access to anti-Cyclopropylcarbinol Derivatives

Abstract

[reaction: see text] Cyclopropenylcarbinol derivatives are regio- and diastereoselectively reduced with LiAlH(4) in Et(2)O into trans-cyclopropylcarbinols as a single isomer. The regioselectivity of the hydroalumination reaction on the cyclopropenyl ring has been mapped out by deuterium labeling experiments.

Gold(I)‐Catalysed Cycloisomerisation of 1,6‐Cyclopropene‐enes

“…[37] This result indicated an S configuration for the hydroxyl-substituted stereocentre in alcohol 15. Additionally, hydroalumination of the minor cyclopropenylcarbinol 14 [38] and subsequent treatment of the resulting compound 17 with DDQ (anhydrous conditions) provided para-methoxybenzylidene acetal 18 (52 %, 83:17 epimeric mixture at the acetal stereocentre), the relative configuration of which was confirmed by 1 H NMR spectroscopy (Scheme 10). Application of the Felkin-Anh model [39] would have predicted cyclopropenylcarbinol 14 to be the major diastereomer, which is not experimentally observed.…”

Metal Mediated and Catalyzed Nucleophilic Additions to Cyclopropenes

“…Recently, Zohar and Marek have shown that the diastereoselectivity of the LiAlH 4 reduction of cyclopropenes can be controlled when the substrate is a secondary allylic alcohol [90]. The diastereoselectivity is particularly high when the substrates are derivatives of 3,3dimethylcyclopropene.…”

Diastereodivergent Carbometalation/Oxidation/Selective Ring Opening: Formation of All‐Carbon Quaternary Stereogenic Centers in Acyclic Systems

“…[7] Ideally, if one could prepare these quaternary stereocenters in a single-pot operation from simple starting materials through a selective carbon-carbon bond activation, it would not only answer this challenging synthetic problem but also pave the way for the efficient formation of new functionalized adducts.Our plan was to initially perform a diastereoselective carbometalation reaction of the cyclopropenyl ester 1 to give the diastereomerically enriched functionalized cyclopropylmetal species 2 (Scheme 1). [8] Then, in a subsequent step, 2 would be oxidized into the corresponding metal cyclopropanolate 3 which would undergo a regioselective ring-opening reaction to provide the versatile metal homoenolate 4. [9] Aldehydes 5, bearing the expected all-carbon quaternary stereocenters in acyclic system, would then be obtained after acid hydrolysis, The entire sequence would proceed in a single pot from the starting alkene.…”

“…[11] Importantly, the metal-catalyzed enantioselective cyclopropenation of terminal alkynes with diazoacetate and Rh II , Co II , or Ir II catalysts are well established methods and as a result, 2-substituted 2-cyclopropenecarboxylic acid esters (1) are easily obtained with excellent enantiomeric ratios and yields. [8,12] So, from the enantiomerically enriched 1, easily prepared from simple terminal alkynes, the formation of these challenging aldehydes (5) could be carried out in a single-pot operation through a sequence of diastereoselective carbometalation/oxidation/ selective ring-opening reactions (Scheme 1).The diastereoselectivity of the carbometalation should be controlled by the stereogenicity of the carbon atom holding the ester moiety (C1; Scheme 1). In the subsequent reactions, this point of chirality is transferred upon selective C3ÀC1 bond activation to give the enolate 4 with an all-carbon stereogenic center.…”

“…To reach such functionalized molecular architectures (e.g., 5) with high enantiomeric ratios, highly diastereoselective carbometalation of cyclopropenes is therefore required. [8,13] Scheme 1. Proposed diastereoselective carbometalation/oxidation/ selective ring-opening reactions.…”