Allenes in Catalytic Asymmetric Synthesis and Natural Product Syntheses

Abstract

Allenes are the simplest class of cumulenes, with two contiguous C=C bonds, and show unique physical and chemical properties. These features make allenes particularly attractive in modern organic chemistry. In this Review, attention is paid to the advances made in catalytic asymmetric synthesis and natural product syntheses based on well-established reactions of allenes, such as propargylation, addition, cycloaddition, cycloisomerization, cyclization, etc., with or without catalysts. Their versatile reactivity, substituent-loading ability, axial to center chirality transfer, and controllable selectivity allow access to target molecules by unique and efficient approaches. The main topics in this Review are presented with selected examples from 2003 to 2011.

6.08 Acylation-Type Reactions: Synthesis of Esters via Acyl Transfer

“…Allenes present a synthetically very useful class of axially chiral compounds. 155 Yet, short synthetic routes for the enantioselective synthesis of axial, helical, and planar chiral allenyl derivatives are rare. Deska and Bäckvall introduced the first DKR of allenols mediated by a palladium complex in combination with the enzyme porcine pancreatic lipase (PPL).…”

Importance of Intermolecular Hydrogen Bonding for the Stereochemical Control of Allene–Enone (3+2) Annulations Catalyzed by a Bifunctional, Amino Acid Derived Phosphine Catalyst

“…[4] This reaction unifies simple allenoate esters and enones under the catalysis of an amino acid derived b-aminophosphine with good to excellent selectivity.S ince then, several other organophosphine catalysts derived from amino acids have been reported for this and related reactions. [5,6] All these catalysts feature ah ydrogen-bonding group (amide or thiourea) vicinal to ad iphenylphosphine group.T od elineate the interactions responsible for enantioselectivity in this important class of transformations,w es tudied the initial reaction reported by Cowen and Miller. Therole of the functional groups and the origin of stereoselectivity in this transformation were established by computational investigation of the bond-forming steps of the reaction mechanism.…”

Combining NHC–Cu and Brønsted Base Catalysis: Enantioselective Allylic Substitution/Conjugate Additions with Alkynylaluminum Reagents and Stereospecific Isomerization of the Products to Trisubstituted Allenes

“…[1] Research in more recent years has been focused on the development of catalytic enantioselective protocols that generate allenes [1] or on providing access to molecules that contain them. [2] Various procedures have been introduced for site-, chemo-, and/or stereoselective allene functionalization.…”

“…[2] Various procedures have been introduced for site-, chemo-, and/or stereoselective allene functionalization. [3] Nonetheless, methods of preparation have been largely centered on disubstituted variants; [1] protocols that furnish the trisubstituted allenes, especially those that are catalytic, are less common and typically involve nucleophilic S N 2' additions to enantiomerically enriched alkynyl entities. [4] Among alternative approaches, strategies that deliver trisubstituted allenes through catalytic isomerization of alkyne-containing substrates [5] pose an attractive but somewhat uncharted pathway.…”