Catalytic Hydrofunctionalization Reactions of 1,3-Diynes

Metal-catalyzed hydrofunctionalization reactions of alkynes, i.e., the addition of Y–H units (Y = heteroatom or carbon) across the carbon–carbon triple bond, have attracted enormous attention for decades since they allow the straightforward and atom-economic access to a wide variety of functionalized olefins and, in its intramolecular version, to relevant heterocyclic and carbocyclic compounds. Despite conjugated 1,3-diynes being considered key building blocks in synthetic organic chemistry, this particular class of alkynes has been much less employed in hydrofunctionalization reactions when compared to terminal or internal monoynes. The presence of two C≡C bonds in conjugated 1,3-diynes adds to the classical regio- and stereocontrol issues associated with the alkyne hydrofunctionalization processes’ other problems, such as the possibility to undergo 1,2-, 3,4-, or 1,4-monoadditions as well as double addition reactions, thus increasing the number of potential products that can be formed. In this review article, metal-catalyzed hydrofunctionalization reactions of these challenging substrates are comprehensively discussed.

Synthesis of Functionalised Cyclohexanes from Carbohydrates

<p>Beta-D-glucopyranose pentaacetate was photobrominated to give the 5-baromide from which 6-deoxy-Beta-D-xylo-hex-5-enopyranose tetraacetate was obtained by reductive elimination. This reaction sequence represents an efficient new route to the 5-ene. A detailed investigation into the photobromination of Beta-D-glucopyranose pentaacetate with bromine and with NBS led to the isolation of several by-products containing bromine substituents at C-1 and/or C-5; their reactions with zinc-acetic acid were studied, and the conformations. in solution of four alkenes derived from the 5-bromo compound were determined. 2,3,4-Triacylated 2,3,4,5-tetrahydroxycyclohexanones were Obtained by mercury (II) catalysed rearrangement of 5-deoxyhex-5-enopyranose esters. The mechanism of this rearrangement, and some enopyranose esters The mechanism of this rearrangement, reactions of the products were examined. The use of these new carbocyclic compounds in the synthesis of branched-chain cyclitol derivatives was explored. By means of diazomethane or, alternatively, hydrogen cyanide, substituted cyclohexanes with one-carbon branches and tertiary hydroxyl groups at the site of chain-branching were preared. Attempts to eliminate water from these tertiary alcohols to give substituted cyclohexene-carbonitriles or -carbaldehydes were unsuccessful.</p>

Synthesis of Functionalised Cyclohexanes from Carbohydrates

<p>Beta-D-glucopyranose pentaacetate was photobrominated to give the 5-baromide from which 6-deoxy-Beta-D-xylo-hex-5-enopyranose tetraacetate was obtained by reductive elimination. This reaction sequence represents an efficient new route to the 5-ene. A detailed investigation into the photobromination of Beta-D-glucopyranose pentaacetate with bromine and with NBS led to the isolation of several by-products containing bromine substituents at C-1 and/or C-5; their reactions with zinc-acetic acid were studied, and the conformations. in solution of four alkenes derived from the 5-bromo compound were determined. 2,3,4-Triacylated 2,3,4,5-tetrahydroxycyclohexanones were Obtained by mercury (II) catalysed rearrangement of 5-deoxyhex-5-enopyranose esters. The mechanism of this rearrangement, and some enopyranose esters The mechanism of this rearrangement, reactions of the products were examined. The use of these new carbocyclic compounds in the synthesis of branched-chain cyclitol derivatives was explored. By means of diazomethane or, alternatively, hydrogen cyanide, substituted cyclohexanes with one-carbon branches and tertiary hydroxyl groups at the site of chain-branching were preared. Attempts to eliminate water from these tertiary alcohols to give substituted cyclohexene-carbonitriles or -carbaldehydes were unsuccessful.</p>

Alkoxyallenes as Starting Materials for the Syntheses of Natural Products

Alkoxyallenes are easily available and versatile building blocks for the preparation of a variety of natural products (terpenes, polyketides, alkaloids, amino acids, carbohydrates etc.) originating from different classes. The synthetic use of the three allene carbon atoms frequently follows the “normal” reactivity pattern showing that alkoxyallenes can be regarded as special enol ethers. Additions of alcohols or amines to alkoxyallenes form vinyl-substituted O,O- or N,O-acetals that are frequently used in ring-closing metathesis reactions. This methodology delivers crucial heterocyclic units of the target compounds. Enantioselective additions provide products with high enantiopurity. Alternatively, an “Umpolung” of reactivity of alkoxyallenes is achieved by lithiation at C-1 and subsequent reaction with electrophiles, such as alkyl halides, carbonyl compounds, imines or nitrones. High stereoselectivity of the addition step can be achieved by substrate control or auxiliary control. The high diastereo- or enantioselectivity is transferred to the subsequent acyclic or cyclic products. The cyclization of primary addition products occurs efficiently under mild conditions and provides functionalized dihydrofuran, dihydropyrrole or 1,2-oxazine derivatives. These are valuable intermediates for the synthesis of a variety of heterocyclic natural products. Nazarov cyclizations or gold catalyzed rearrangements allow the synthesis of five- and six-membered carbocyclic compounds that are also used for natural product synthesis. Dedicated to Dr. Reinhold Zimmer, a pioneer of alkoxyallene chemistry, on the occasion of his 60th birthday.

Recent Advances in the Synthesis of Hetero- and Carbocyclic Compounds­ and Complexes Based on Acenaphthylene-1,2-dione

Acenaphthylene-1,2-dione has been utilized in a wide range of reactions as a starting material for the synthesis of hetero- and carbocyclic compounds and complexes. This review provides a short summary of the recent advances in the application of acenaphthylene-1,2-dione in the synthesis of hetero- and carbocyclic systems and bioactive compounds. In addition, the applications of acenaphthylene-1,2-dione in the synthesis of spiro compounds, propellanes, and ligands in catalyst reactions, from 2002 to early 2018, are included.1 Introduction2 Synthesis of Spiro Compounds Employing Acenaphthylene-1,2-dione2.1 Methods for the Construction of Spiro Compounds2.1.1 By 1,3-Dipolar Cycloaddition of Acenaphthylene-1,2-dione via Azomethine Ylides2.1.2 By Multicomponent Reactions of Acenaphthylene-1,2-dione with C–H Acidic Compounds2.1.3 By Reaction of Acenaphthylene-1,2-dione with Zwitterionic Intermediates2.1.4 By Substitution and Multicomponent Reactions of Acenaphth- ylene-1,2-dione with Different Nucleophiles3 Synthesis of Propellanes by Employing Acenaphthylene-1,2-dione3.1 Methods for the Construction of Propellanes Based on Acenaph- thylene-1,2-dione3.1.1 By Reaction of Acenaphthylene-1,2-dione with Nucleophiles3.1.2 By Reaction of Acenaphthylene-1,2-dione with Binucleophiles4 Synthesis of Ligands Employing Acenaphthylene-1,2-dione for Catalyst Reactions5 Synthesis of Novel Hetero- and Carbocyclic Compounds Employing Acenaphthylene-1,2-dione5.1 By Reaction of Acenaphthylene-1,2-dione with Nucleophiles5.2 By Reaction of Acenaphthylene-1,2-dione with Zwitterionic Intermediates5.3 By Ring Opening and Ring Enlargement6 Conclusion

Metal-Catalyzed Oxidative Coupling of Ketones and Ketone Enolates

Recent years have witnessed a significant advancement in the field of radical oxidative coupling of ketones towards the synthesis of highly useful synthetic building blocks, such as 1,4-dicarbonyl compounds, and biologically important heterocyclic and carbocyclic compounds. Besides oxidative homo- and cross-coupling of enolates, other powerful methods involving direct C(sp3)–H functionalizations of ketones­ have emerged towards the synthesis of 1,4-dicarbonyl compounds. Moreover, direct α-C–H functionalization of ketones has also allowed an efficient access to carbocycles and heterocycles. This review summarizes all these developments made since 2008 in the field of metal-catalyzed/promoted radical-mediated functionalization of ketones at the α-position.1 Introduction2 Synthesis of 1,4-Dicarbonyl Compounds3 Synthesis of Heterocyclic Scaffolds4 Synthesis of Carbocyclic Scaffolds5 Conclusion