https://pubs.rsc.org/en/content/articlepdf/2019/NP/C8NP00092A

Marine natural products.

The direct functionalization of C-H bonds in organic compounds has recently emerged as a powerful and ideal method for the formation of carbon-carbon and carbon-heteroatom bonds. This Review provides an overview of C-H bond functionalization strategies for the rapid synthesis of biologically active compounds such as natural products and pharmaceutical targets.

C-H bond functionalization: emerging synthetic tools for natural products and pharmaceuticals

In studying the evolution of organic chemistry and grasping its essence, one comes quickly to the conclusion that no other type of reaction plays as large a role in shaping this domain of science than carbon-carbon bond-forming reactions. The Grignard, Diels-Alder, and Wittig reactions are but three prominent examples of such processes, and are among those which have undeniably exercised decisive roles in the last century in the emergence of chemical synthesis as we know it today. In the last quarter of the 20th century, a new family of carbon-carbon bond-forming reactions based on transition-metal catalysts evolved as powerful tools in synthesis. Among them, the palladium-catalyzed cross-coupling reactions are the most prominent. In this Review, highlights of a number of selected syntheses are discussed. The examples chosen demonstrate the enormous power of these processes in the art of total synthesis and underscore their future potential in chemical synthesis.

Palladium-catalyzed cross-coupling reactions in total synthesis.

4.2.8. Reductive Coupling 3109 5. Reaction of Aromatic Compounds 3110 5.1. Electrophilic Substitutions 3110 5.2. Radical Substitution 3111 5.3. Oxidative Coupling 3111 5.4. Photochemical Reactions 3111 6. Reaction of Carbonyl Compounds 3111 6.1. Nucleophilic Additions 3111 6.1.1. Allylation 3111 6.1.2. Propargylation 3120 6.1.3. Benzylation 3121 6.1.4. Arylation/Vinylation 3121 6.1.5. Alkynylation 3121 6.1.6. Alkylation 3121 6.1.7. Reformatsky-Type Reaction 3122 6.1.8. Direct Aldol Reaction 3122 6.1.9. Mukaiyama Aldol Reaction 3124 6.1.10. Hydrogen Cyanide Addition 3125 6.2. Pinacol Coupling 3126 6.3. Wittig Reactions 3126 7. Reaction of R,â-Unsaturated Carbonyl Compounds 3127

Organic Reactions in Aqueous Media with a Focus on Carbon−Carbon Bond Formations: A Decade Update

The design and implementation of cascade reactions is a challenging facet of organic chemistry, yet one that can impart striking novelty, elegance, and efficiency to synthetic strategies. The application of cascade reactions to natural products synthesis represents a particularly demanding task, but the results can be both stunning and instructive. This Review highlights selected examples of cascade reactions in total synthesis, with particular emphasis on recent applications therein. The examples discussed herein illustrate the power of these processes in the construction of complex molecules and underscore their future potential in chemical synthesis.

Cascade reactions in total synthesis.

The first synthesis of a highly functionalized B-homo-C-nor grayanotoxin closely related to kalmanol is reported. An enantiocontrolled route to the diquinane sector was first developed from (4R)-(+)-tert-butyldimethylsiloxycyclopentenone by taking advantage of the Michael acceptor properties of this enone and an α,β-unsaturated ester subsequently derived from it, viz., 4 → 7 → 8. These experiments formed the basis for more advanced substitution of the bicyclo[3.3.0]octane core. In fact, ready access was gained to the α-hydroxy esters 24−27. In these advanced intermediates, it is imperative that the acetyl and carbomethoxy groups bear a trans 1,3-relationship. The neighboring OR substituent should preferably be larger than methoxy in order to guarantee 100% facial selectivity during the ensuing capture by 1 (as its lithiated derivative). This condensation leads unidirectionally to tricyclic lactones represented by 30 and 31 and sets the stage for implementation of sequential Tebbe olefination and Claisen r...

Studies Directed to the Synthesis of the Unusual Cardiotoxic Agent Kalmanol. Enantioselective Construction of the Advanced Tetracyclic 7-Oxy-5,6-dideoxy Congener

The reaction of open-chain or cyclic α-diketones with specific ω-alkenyl organometallics leads readily under the proper conditions to 1,2-diols bonded to terminal olefinic chains. With 1-phenyl-1,2-propanedione, biacetyl, and cyclohexane-1,2-dione, allylindation in aqueous THF proceeds readily at both adjacent carbonyls. For cyclododecane-1,2-dione, recourse must be made to allylmagnesium bromide for completing the second-stage condensation. Grignard reagents have also served well as reactants for biacetyl monoadducts. In contrast, monoallylated camphorquinone is reluctant to couple to Grignard reagents and reacts only when Barbier-type alkyllithium reactions are applied. The ring closing metatheses of these products have been examined. Where six-membered ring formation operates, cyclization can be performed directly on diols. When larger rings are involved, the diols will react only if structural preorganization capable of facilitating mutual approach of the two double bonds is at play. For this purpose,...

Intercalation of Multiple Carbon Atoms between the Carbonyls of α-Diketones

Molecular ladders constituted of laterally-fused 1,4-cyclohexadiene subunits. Open-chain models of the [n]beltenes.

Electronic control of stereoselectivity. 9. The stereochemical course of electrophilic additions to aryl-substituted benzobicyclo[2.2.2]octadienes

Following an improved preparation of 2-methylene-1,3-dithiolane, this ketene acetal was shown to undergo inverse-electron-demand Diels-Alder cycloaddition to tropone. Regiocontrolled copper hydride reduction and resolution via sulfoximine adducts was readily achieved to give (-)-(9). Addition to (9) of the chiral nonracemic vinyl bromides (21) and (22) proceeded with endo capture of the nucleophilic vinyllithium to give carbinols that underwent anionic oxy-Cope rearrangement at somewhat elevated temperatures. The [3,3] sigmatropic event delivered cis,syn, cis-tricyclo[9.3.0.0 2,8 ]tetradecenones possessing structural frame- works related to the cyathins. Once (31) was in hand, it proved an easy matter to introduce added unsaturation and oxygen substituents. The tendency of certain derivatives for transannular cyclization was made quite apparent. Attempts to introduce a C(6)-α-methyl substituent was not achieved, chiefly as the result of the overall molecular concavity of this class of intermediates. A variety of reactions aimed at enhen- cing the level of functionality in rings B and C was explored and processes conducive to the attainment of these goals were developed

Leo A. Paquette

Papers

Studies Directed to the Synthesis of the Unusual Cardiotoxic Agent Kalmanol. Enantioselective Construction of the Advanced Tetracyclic 7-Oxy-5,6-dideoxy Congener

Intercalation of Multiple Carbon Atoms between the Carbonyls of α-Diketones

Molecular ladders constituted of laterally-fused 1,4-cyclohexadiene subunits. Open-chain models of the [n]beltenes.

Electronic control of stereoselectivity. 9. The stereochemical course of electrophilic additions to aryl-substituted benzobicyclo[2.2.2]octadienes

Exploratory Synthetic Studies Involving the Tricyclo[9.3.0.02,8]tetradecane Ring System Peculiar to the Cyathins