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The synthesis of 2-allenyl-2-substituted-3,3-difluoroindolines has been accomplished, taking advantage of the reaction between N-allenyl-indoles and Selectfluor under iron catalysis.

Gold-catalyzed carbocyclization of the title compounds give corresponding fused tetracyclic indole-β-lactams in modest to good yields with high stereo- and regioselectivities.

The divergent behavior of two homologue allenals, namely, 2-(buta-2,3-dienyloxy)- and 2-(propa-1,2-dienyloxy)benzaldehydes, as cyclization substrates is described. 2-(Buta-2,3-dienyloxy)benzaldehydes suffers a formal allenic carbocyclization reaction to afford chromenes, whereas 2-(propa-1,2-dienyloxy)benzaldehydes react to yield chromones. The formation of chromenes is strictly a formal hydroarylation process divided into two parts, namely, allenic Claisen-type rearrangement and oxycyclization. An unknown N-heterocyclic carbene (NHC)-catalyzed allenic hydroacylation reaction must be invoked to account for the preparation of chromones. ortho-Allenylbenzaldehydes bearing either electron-donating substituents or electron-withdrawing substituents worked well to afford both the hydroarylation and hydroacylation products. This unexpected difference in reactivity can be rationalized by means of density functional theory calculations. more...

The reaction of α-allenols (I) in the presence of PtCl2 as a catalyst results in intramolecular cyclization to dihydrofurans (II) whereas a binary Pt/Ag-catalyst promotes rearrangement to E/Z-mixtures of α,β-unsaturated ketones. more...

For the first time, the access to enantiopure six-membered heterocycles from two different allenes is demonstrated in a chemo- and regioselective palladium-catalyzed cross-coupling reaction.

The gold-catalyzed preparation of 2-azetidinone-fused oxacycles is accomplished from β-lactam-linked enynes through heterocyclization reaction taking advantage of the acetonide pendant group.

In contrast to the reaction of 3-phenoxy(indolyl)allenes (IV), which are transformed into 1-hydroxycarbazoles (V), the corresponding 3-iodo derivatives (I) afford 3-iodocarbazoles (II) through rare recycling of halogen groups via an unprecedented 1,3-halogen migration. more...

The direct approach for the stereoselective synthesis of functionalized enynes by treatment of aryl-substituted α-allenols with an aqueous Ac-Cl/NaOH system possibly proceeds via elimination of acetic acid, made up of a δ-hydrogen and the acetate group in the initially formed α-allenic acetate. more...

Regiocontrolled metal-catalyzed preparations of enantiopure tetrahydrofurans, dihydropyrans, and tetrahydrooxepines have been developed starting from γ-allenols derived from 4-oxoazetidine-2-carbaldehydes and D-glyceraldehyde. Regioselectivity control in the O–C functionalization of γ-allenols can be achieved through the choice of catalyst, protecting group, or tether. Because of the increasing power and availability of computers, and the simultaneous development of well-tested and reliable theoretical methods, the use of computational chemistry as an adjunct to experimental research has increased rapidly. Computational studies can be carried out to assist in understanding experimental data, such as the exploration of reaction mechanisms that are not readily studied by experimental means. As a consequence, density functional calculations were performed to predict the regioselectivity of the γ-allenol cycloetherification to the five-, six-, and seven-membered oxacycles on the basis of the tether nature, the presence of a protecting group, and characteristics of the metals, and to gain insight into the mechanism of the oxycyclizations. The interactions between computational and experimental chemistry are often brief. However, it should be desirable to keep this close association for long periods. This chapter must be considered as an interesting symbiotic relationship on the field of organic synthesis using metal (Au, Pd, and Pt) catalysis. more...

Two different halogenation procedures including both (DHQ)2-PHAL as the enantioselective agent are developed for the preparation of fluorinated heterocyclic scaffolds which are obtained as exclusive cis isomers. more...

The substitution pattern of the allenol substrate determines the reaction outcome of the gold-catalyzed cyclization to yield either dihydrofurans (II)/(VI) or oxetenes (IV)/(VII).

Amino-2-propanol structures can be obtained by addition to dibenzyl acetals of in situ generated dihalocarbenes using LVT (Low Valent Titanium). This methodology can be used to obtain adrenergic β-blockers with amino-2-propanol structure. Tetrahalomethanes are the best dihalocarbene precursors. The yields obtained using halofluoromethanes can be increased by addition of carbontetrachloride. A process that can imply halogen transfer may be proposed. more...

The allene moiety represents an excellent building block for allene cross-coupling cyclization reactions, affording heterocyclic skeletons in a single step. This strategy is of particular interest when two different allene derivatives are involved in a series of metal-catalyzed cross-coupling heterocyclization processes. This Concept article is focused on the Pd-catalyzed union of two different allenic moieties, with cyclization of at least one of them by intramolecular cyclometalation. These new, versatile, and highly effective transformations are complex multistep processes leading to potential privileged structures that could find wide applications in related medicinal chemistry. more...

A new chiral copper (II) catalyst was prepared from Cu(OTf) 2 and chiral pyridine-phosphine ligands 1–2 in dichloromethane and used in the Diels-Alder reaction of 3-acryloyl-1,3-oxazolidine-2-one with cyclopentadiene leading to enantioselectivities up to 99%. more...

The importance of the adrenergic β-blockers with structure of (S) 1-aryloxy-3-amino-2-propanol in the treatment of different diseases has led the development of a variety of stereoselective synthetic methodologies for this stereoisomer. In this review we present several methodologies to obtain this compound using (i) chiral substrates, (ii) chiral catalysts (organometallic or enzymes) and (iii) preparative chiral chromatography, showing the advantages and disadvantages of each methodology. more...

First insights into the reaction between a Baylis-Hillman adduct and an allene moiety have been obtained from the novel domino heterocyclization/cross-coupling reaction of alpha-allenols and Baylis-Hillman acetates, which furnishes [(2,5-dihydrofuran-3-yl)methyl]acrylate derivatives in moderate to good yields. more...

Positive discrimination: Chemo- and regioselective palladium-catalyzed cycloetherification of allendiols, namely beta,gamma- and gamma,delta-allendiols, may occur by judicious choice of palladium-catalyzed conditions owing to their potential ability to discriminate between both nucleophilic sites (see scheme). more...

Reactions of tetrahydrothiophene-3-carbaldehydes with stabilized organometallic reagents were investigated in aqueous media. Tetrahydrothiophene-3-carbaldehydes and a variety of stabilized organic halides undergo stereocontrolled coupling under Barbier-type conditions in the presence of different metals (zinc, tin, indium) and additives [ammonium chloride, hydrobromic acid, hafnium(IV) chloride, bismuth(III) chloride]. The regiochemistry of the carbonyl addition processes, when applicable, was excellent.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008) more...

A novel approach to enantiopure spirocyclic β-lactams has been developed by using different intramolecular metal-catalyzed cyclization reactions in monocyclic unsaturated alcohols. The access to cyclization precursors, 2-azetidinone-tethered homoallylic alcohols, (buta-1,3-dien-2-yl)methanols, and α-allenols was achieved by regio and stereoselective addition of stabilized organo-indium reagents to azetidine-2,3-diones in aqueous environment. more...