Hydroxy-Directed Cyclopropanation of Esters: Synthesis of Trisubstituted Cyclopropanols

Recent advances in asymmetric synthesis via cyclopropanol intermediates

Cyclopropanols have attracted significant attention in organic synthesis as versatile three-carbon synthons, as this readily available class of donor-activated cyclopropanes undergoes miscellaneous transformations, either via ring-opening or with retention of the cyclopropane ring. This review summarizes stereoselective and stereoretentive transformations suitable for asymmetric synthesis. The utility of cyclopropanols is discussed for two main strategies: (i) substrate-controlled transformations using enantiomerically enriched cyclopropanol intermediates through a traditional approach, and (ii) the use of nonchiral or racemic cyclopropanols, where asymmetric induction is achieved through a chiral catalyst, representing a direction that has recently emerged.

Developments in the construction of cyclopropanols

The ring-opening of cyclopropanols is one of the most active areas of research and it has been well documented in recent years owing to subsequent coupling with various partners, thus providing the facile syntheses of a large number of multifunctional compounds that may otherwise be difficult to access. Evidently, the useful cascade reaction requires easy access to diversely functionalized cyclopropanol substrates. However, developments in the construction of cyclopropanols have not received adequate attention. Herein, recent reports on the formation of cyclopropanols are summarized, and the highly stereoselective production of new promising substrates for the cyclopropanol ring-opening/cross-coupling reactions are introduced and improved syntheses of known cyclopropanols are depicted. This review may facilitate more interesting applications of the cyclopropanol ring-opening/coupling reaction in the synthesis of pharmaceutical compounds, natural products, and structurally more diversified organic synthetic intermediates.

Pd-Catalyzed Selective Remote Ring Opening of Polysubstituted Cyclopropanols

The distant functionalization of ω-ene cyclopropanols is induced by a Pd-catalyzed Heck reaction triggering a "metal-walk" and selective ring-opening of the three-membered ring. This approach provides a new class of acyclic aldehydes possessing concomitantly a stereodefined double bond and a quaternary carbon stereocenter α to the carbonyl group.

Asymmetric Catalytic Preparation of Polysubstituted Cyclopropanol and Cyclopropylamine Derivatives

The catalytic asymmetric carbometalation of cyclopropenes followed by either an electrophilic oxidation or amination reaction provides a unique approach to the formation of diastereomerically pure and enantiomerically enriched cyclopropanol and cyclopropylamine derivatives, respectively.

Titanium carbenoid-mediated cyclopropanation of allylic alcohols: selectivity and mechanism

A new method for the chemo- and stereoselective conversion of allylic alcohols into the corresponding cyclopropane derivatives has been developed. The cyclopropanation reaction was carried out with an unprecedented titanium carbenoid generated in situ from Nugent's reagent, manganese and methylene diiodide. The reaction involving the participation of an allylic hydroxyl group, proceeded with conservation of the alkene geometry and in a high diastereomeric excess. The scope, limitations and mechanism of this metal-catalysed reaction are discussed.

Allylsamarium Bromide-Mediated Cascade Cyclization of Homoallylic Esters. Synthesis of 2-(2-Hydroxyalkyl)cyclopropanols and 2-(2-Hydroxyethyl)bicyclo[2.1.1]hexan-1-ols

In continuation of our previous study on the intramolecular reductive coupling of simple homoallylic esters promoted by allylSmBr/HMPA/H2O, which afforded a facile synthesis of 2-(2-hydroxyalkyl)cyclopropanols, here we report the reductive cascade cyclization of but-3-enyl but-3-enoates mediated by allylSmBr/HMPA/CuCl2·2H2O, in which the two C═C bonds were successively coupled to allow the construction of the structurally interesting bridged bicyclic tertiary alcohols. Thus, the 2-(2-hydroxyethyl)bicyclo[2.1.1]hexan-1-ols were prepared in moderate to good yields with excellent diastereoselectivity.