Synthesis Of Carbocycles Research Articles

ChemInform Abstract: Formal [4+1] Annulation Reactions in the Synthesis of Carbocyclic and Heterocyclic Systems

AbstractReview: 546 refs.

Rhodium-catalyzed [5 + 2 + 1] cycloaddition of ene-vinylcyclopropanes and CO: reaction design, development, application in natural product synthesis, and inspiration for developing new reactions for synthesis of eight-membered carbocycles.

Practical syntheses of natural products and their analogues with eight-membered carbocyclic skeletons are important for medicinal and biological investigations. However, methods and strategies to construct the eight-membered carbocycles are limited. Therefore, developing new methods to synthesize the eight-membered carbocycles is highly desired. In this Account, we describe our development of three rhodium-catalyzed cycloadditions for the construction of the eight-membered carbocycles, which have great potential in addressing the challenges in the synthesis of medium-sized ring systems. The first reaction described in this Account is our computationally designed rhodium-catalyzed two-component [5 + 2 + 1] cycloaddition of ene-vinylcyclopropanes (ene-VCPs) and CO for the diastereoselective construction of bi- and tricyclic cyclooctenones. The design of this reaction is based on the hypothesis that the C(sp(3))-C(sp(3)) reductive elimination of the eight-membered rhodacycle intermediate generated from the rhodium-catalyzed cyclopropane cleavage and alkene insertion, giving Wender's [5 + 2] cycloadduct, is not easy. Under CO atmosphere, CO insertion may occur rapidly, converting the eight-membered rhodacycle into a nine-membered rhodacycle, which then undergoes an easy C(sp(2))-C(sp(3)) reductive elimination process and furnishes the [5 + 2 + 1] product. This hypothesis was supported by our preliminary DFT studies and also served as inspiration for the development of two [7 + 1] cycloadditions: the [7 + 1] cycloaddition of buta-1,3-dienylcyclopropanes (BDCPs) and CO for the construction of cyclooctadienones, and the benzo/[7 + 1] cycloaddition of cyclopropyl-benzocyclobutenes (CP-BCBs) and CO to synthesize the benzocyclooctenones. The efficiency of these rhodium-catalyzed cycloadditions can be revealed by the application in natural product synthesis. Two eight-membered ring-containing natural products, (±)-asterisca-3(15),6-diene and (+)-asteriscanolide, have been synthesized using the [5 + 2 + 1] cycloaddition as the key step. In the latter case, excellent asymmetric induction was obtained using a chiral substrate. The efficiency of the [5 + 2 + 1] reaction was further demonstrated by the synthesis of four sesquiterpene natural products, (±)-pentalenene, (+)-hirsutene, (±)-1-desoxyhypnophilin, and (±)-hirsutic acid C, containing linear or branched triquinane skeletons utilizing the tandem or stepwise [5 + 2 + 1] cycloaddition/aldol reaction strategy. With the success of [5 + 2 + 1] cycloaddition in natural product synthesis, application of the [7 + 1] and benzo/[7 + 1] cycloadditions in target- and function-oriented syntheses can be envisioned.

An Arylative Ring Expansion Cascade of Fused Cyclobutenes via Short-Lived Intermediates with Planar Chirality.

An arylative ring expansion cascade has been developed for the synthesis of medium-sized carbocycles from fused cyclobutenes. This reaction proceeds through a short-lived cis,trans-cycloalkadiene intermediate that is formed by thermal 4π electrocyclic ring opening. Chirality transfer experiments provide direct evidence for the transient generation of the intermediate.

ChemInform Abstract: Enantioselective Synthesis of cis‐Fused Cyclooctanoids via Rhodium(I)‐Catalyzed [4 + 2 + 2] Cycloadditions.

Abstract[4 + 2] Cycloadducts are formed as sideproducts in 23‐47% yield.

ChemInform Abstract: Rhodium‐Catalyzed C—H Activation of Phenacyl Ammonium Salts Assisted by an Oxidizing C—N Bond: A Combination of Experimental and Theoretical Studies.

Rh(III)-catalyzed C–H activation assisted by an oxidizing directing group has evolved to a mild and redox-economic strategy for the construction of heterocycles. Despite the success, these coupling systems are currently limited to cleavage of an oxidizing N–O or N–N bond. Cleavage of an oxidizing C–N bond, which allows for complementary carbocycle synthesis, is unprecedented. In this article, α-ammonium acetophenones with an oxidizing C–N bond have been designed as substrates for Rh(III)-catalyzed C–H activation under redox-neutral conditions. The coupling with α-diazo esters afforded benzocyclopentanones, and the coupling with unactivated alkenes such as styrenes and aliphatic olefins gave ortho-olefinated acetophenoes. In both systems the reactions proceeded with a broad scope, high efficiency, and functional group tolerance. Moreover, efficient one-pot coupling of diazo esters has been realized starting from α-bromoacetophenones and triethylamine. The reaction mechanism for the coupling with diazo este...

Formal [4+1] annulation reactions in the synthesis of carbocyclic and heterocyclic systems.

Formal [4+1] annulation reactions in the synthesis of carbocyclic and heterocyclic systems.

Ring-closing enyne metathesis of terminal alkynes with propargylic hindrance.

The ring closing enyne metathesis of substrates with propargylic hindrance was investigated, revealing the successful combination of the Stewart-Grubbs catalysts and microwave heating sometimes up to 170 °C for oxacycles. Medium-sized rings were obtained from terminal alkynes previously reputed as reluctant substrates. This unmatched combination was applied to the synthesis of carbocycles and oxacycles. In addition, this is the first report on the use of the Stewart Grubbs catalyst in ring closing enyne metatheses.

ChemInform Abstract: 3‐Alkyloxycyclobutanones as Useful Synthons for Heterocycle and Carbocycle Synthesis

AbstractReview: [formal [4 + 2], [3 + 2], and [3 + 3] annulations as well as other types of transformations with 3‐alkyloxycyclobutanones, 34 refs.

Hypervalent Iodine(III)‐Mediated Benzannulation of Enamines with Alkynes: an Efficient Synthesis of Substituted Aminonaphthoic Acid Derivatives

Abstract An intermolecular two CC bond formation procedure for the synthesis of carbocycles mediated by hypervalent iodine(III) reagents was developed. This metal free protocol provided a new approach for the synthesis of useful substituted 1‐amino‐2‐naphthoic acid derivatives via benzannulation reactions. Various N‐unsubstituted and N‐alkyl substituted aromatic enamines with terminal alkynes and non‐terminal alkynes can be converted into corresponding 1‐amino‐2‐naphthoic acid derivatives under mild reaction conditions. When meta‐substituted phenyl enamines were employed in the reaction, two cyclization paths were detected in the reaction and ortho‐cyclization products were the only or major products. Good functional group tolerance, readily available material and high atom utilization efficiency make this method a potential procedure which may find broad application in organic synthesis.

Enantioselective synthesis of cis-fused cyclooctanoids via rhodium(I)-catalyzed [4 + 2 + 2] cycloadditions.

Catalytic multicomponent [m + n + o]-type cycloadditions offer efficient, atom-economical routes to diverse complex carbocycles. Recently, such transformations have emerged as unique strategies for medium ring carbocycle synthesis. Despite the important developments in this area, however, highly enantioselective [m + n + o]-type processes accessing medium ring carbocycles have yet to be developed. Herein, a rhodium-catalyzed [4 + 2 + 2] cycloaddition of allenedienes with allenes enabling the direct stereoselective synthesis of cis-fused cyclooctanoids is reported. These cycloadditions are successful with a diverse range of π-components and demonstrate the potential for high levels of enantioselectivity in a [4 + 2 + 2] process.

Rhodium-catalyzed C-H activation of phenacyl ammonium salts assisted by an oxidizing C-N bond: a combination of experimental and theoretical studies.

Rh(III)-catalyzed C-H activation assisted by an oxidizing directing group has evolved to a mild and redox-economic strategy for the construction of heterocycles. Despite the success, these coupling systems are currently limited to cleavage of an oxidizing N-O or N-N bond. Cleavage of an oxidizing C-N bond, which allows for complementary carbocycle synthesis, is unprecedented. In this article, α-ammonium acetophenones with an oxidizing C-N bond have been designed as substrates for Rh(III)-catalyzed C-H activation under redox-neutral conditions. The coupling with α-diazo esters afforded benzocyclopentanones, and the coupling with unactivated alkenes such as styrenes and aliphatic olefins gave ortho-olefinated acetophenoes. In both systems the reactions proceeded with a broad scope, high efficiency, and functional group tolerance. Moreover, efficient one-pot coupling of diazo esters has been realized starting from α-bromoacetophenones and triethylamine. The reaction mechanism for the coupling with diazo esters has been studied by a combination of experimental and theoretical methods. In particular, three distinct mechanistic pathways have been scrutinized by DFT studies, which revealed that the C-H activation occurs via a C-bound enolate-assisted concerted metalation-deprotonation mechanism and is rate-limiting. In subsequent C-C formation steps, the lowest energy pathway involves two rhodium carbene species as key intermediates.

Seven-membered rings through metal-free rearrangement mediated by hypervalent iodine.

A versatile and metal-free approach for the synthesis of carbocycles and of heterocycles bearing seven- and eight-membered rings is described. The strategy is based on ring expansion of 1-vinylcycloalkanols (or the corresponding silyl or methyl ether) mediated by the hypervalent iodine reagent HTIB (PhI(OH)OTs). Reaction conditions can be easily adjusted to give ring expansion products bearing different functional groups. A route to medium-ring lactones was also developed.

Exploitation of in situ generated sugar-based olefin keto-nitrones: synthesis of carbocycles, heterocycles, and nucleoside derivatives.

Application of intramolecular 1,3-dipolar nitrone cycloaddition reaction on carbohydrate-derived precursors containing an olefin functionality at C-1 or C-3 or C-5 and a nitrone moiety at C-2 or C-3 as appropriate has resulted in the formation of structurally new cycloaddition products containing furanose-fused oxepane, thiepane, azepane, cyclopentane, cycloheptane, tetrahydrofuran, and pyranose-fused tetrahydrofuran rings. The structure and stereochemistry of these products have been characterized by spectral as well as single-crystal X-ray analyses. Two of the compounds have been transformed to the bicyclic nucleoside derivatives applying Vorbrüggen reaction conditions.

3‐Alkyloxycyclobutanones as Useful Synthons for Heterocycle and Carbocycle Synthesis

AbstractSubstituted 3‐alkyloxycyclobutanones are highly valuable intermediates in organic synthesis, which demonstrate interesting and rich reactivity in different types of reactions due to the strain energy. Under Lewis acid catalysis, 3‐alkyloxycyclobutanones can form zwitterionic intermediates and participate in a series of cycloaddition reactions as three‐ or four‐carbon synthons. This Focus Review will mainly discuss formal [4+2], [3+2], and [3+3] annulations as well as other types of transformations with 3‐alkyloxycyclobutanones.

ChemInform Abstract: Nitroalkenes in the Synthesis of Carbocyclic Compounds

AbstractReview: [16 refs.

Enantioselective synthesis of polycyclic carbocycles via an alkynylation-allylation-cyclization strategy.

A new general three-stage strategy to access polycyclic ring systems bearing all-carbon quaternary centers with high enantioselectivity is reported. The required starting materials were readily accessed in racemic form through the α-alkynylation of ketoesters with EBX (EthynylBenziodoXolone) hypervalent iodine reagents. A Pd-catalyzed asymmetric decarboxylation allylation was then achieved in high yields and enantioselectivities with Trost's biphosphine ligands. Finally, transition-metal catalyzed cyclization of the obtained chiral enynes gave access to fused and spiro polycyclic ring systems constituting the core of many bioactive natural products.

Intermolecular [3+2] Annulation of Cyclopropylanilines with Alkynes, Enynes, and Diynes via Visible Light Photocatalysis.

One-step synthesis of carbocycles substituted with amines from simple starting materials remains rare. We recently developed intermolecular [3+2] annulation of cyclopropylanilines with alkenes and alkynes that enable this one-step synthesis. Herein, we report our findings for a fullscale study of the annulation. Significant expansion of the substrate scope for both cyclopropylanilines and alkynes is achieved. A range of structurally diverse carbocycles substituted with amines is prepared.

N‐Heterocyclic Carbene‐Catalyzed All Carbon‐[4+2] Cyclocondensation of α,β‐Unsaturated Acyl Chlorides with 3‐Alkylenyloxindoles

AbstractAlthough the NHC‐catalyzed cyclization reactions have been well established for the synthesis of various heterocycles, the corresponding all carbon cyclization reaction for the synthesis of carbocycles is far less established. In this note, the NHC‐catalyzed all carbon [4+2] cyclocondensation of α,β‐unsaturated acyl chlorides and 3‐alkenyloxindoles was developed to give the corresponding spirocarbocyclic oxindoles in good yield with good to high diastereoselectivities.

Highly regioselective SN2′ reaction of β-fluoroallylic phosphates with organocopper reagents and its application to the synthesis of fluorine-containing carbocycles

Treatment of β-fluoroallyl phosphates with 2.2 equiv. of organocuprates, prepared readily from 2.2 equiv. each of CuCN and organometallics (organolithium reagents, Grignard reagents, and organozinc reagents), in THF at −40 to 0 °C for 0.25 to 24 h gave γ-products in a highly regioselective manner. Thus obtained γ-adducts were subjected to the ring-closing metathesis, the corresponding cyclic fluoroalkenes being afforded in good yields.

Aerobic copper-catalyzed oxidative [6C+1C] annulation: an efficient route to seven-membered carbocycles.

It has been revealed for the first time that co-promoted by CuCl and NaH in the presence of molecular oxygen (air), the reaction of dicinnamoyl ketene dithioacetals as the acyclic C6 synthons with ethyl cyanoacetate gives functionalized seven-membered carbocycles. A mechanism is proposed involving a tandem Michael addition-intramolecular radical cyclization-benzyl C(sp(3))-H bond oxidation.