Rapid Access to Complex Molecular Architectures viao-Azaquinones

A Metal-free Catalytic Reduction of α,β-unsaturated Carbonyl Compounds with Phenyldimethylsilane

Selective reduction of α,β-unsaturated carbonyl compounds to the corresponding saturated ones by phenyldimethyl silane was promoted by a catalytic amount of I2O5 at ambient temperature in CH2Cl2.

1,8-Bis(silylamido)naphthalene complexes of magnesium and zinc synthesised through alkane elimination reactions

The reactions between magnesium or zinc alkyls and 1,8-bis(triorganosilyl)diaminonaphthalenes afford the 1,8-bis(triorganosilyl)diamidonaphthalene complexes with elimination of alkanes. The reaction between 1,8-C₁₀H₆(NSiMePh₂H)₂ and one or two equivalents of MgⁿBu₂ affords two complexes with differing coordination environments for the magnesium; the reaction between 1,8-C₁₀H₆(NSiMePh₂H)₂ and MgⁿBu₂ in a 1 : 1 ratio affords 1,8-C₁₀H₆(NSiMePh₂)₂{Mg(THF)₂} (1), which features a single magnesium centre bridging both ligand nitrogen donors, whilst treatment of 1,8-C₁₀H₆(NSiR₃H)₂ (R₃ = MePh₂, ⁱPr₃) with two equivalents of MgⁿBu₂ affords the bimetallic complexes 1,8-C₁₀H₆(NSiR₃)₂{ⁿBuMg(THF)}₂ (R₃ = MePh₂2, R₃ = ⁱPr₃3), which feature four-membered Mg₂N₂ rings. Similarly, 1,8-C₁₀H₆(NSiⁱPr₃)₂{MeMg(THF)}₂ (4) and 1,8-C₁₀H₆(NSiMePh₂)₂{ZnMe}₂ (5) are formed through reactions with the proligands and two equivalents of MMe₂ (M = Mg, Zn). The reaction between 1,8-C₁₀H₆(NSiMePh₂H)₂ and two equivalents of MeMgX affords the bimetallic complexes 1,8-C₁₀H₆(NSiMePh₂)₂(XMgOEt₂)₂ (X = Br 6; X = I 7). Very small amounts of [1,8-C₁₀H₆(NSiMePh₂)₂{IMg(OEt₂)}]₂ (8), formed through the coupling of two diamidonaphthalene ligands at the 4-position with concomitant dearomatisation of one of the naphthyl arene rings, were also isolated from a solution of 7.

Total synthesis of the pseudopterosin aglycones

The 15 published total syntheses of the pseudopterosins are reviewed, with focus on strategic considerations and an emphasis on ring formation.

Marine diterpene glycosides

Marine diterpene glycosides (MDGs) respresent a small but highly significant group of the much larger class of marine diterpenes. The three well-studied examples of MDGs are eleutherobins, pseudopterosins and fuscosides, all of which exhibit extremely promising biological activity. The eleutherobins are potent anti-mitotic agents, and the pseudopterosins and fuscosides are potent anti-inflammatory agents. This review discusses the structures and biological activities of these compounds, as well as their biosynthesis and synthesis.

A Convenient Synthesis of the Central Core of Helioporins, seco-Pseudopterosins and Pseudopterosins via BCA-Annulation Sequence

A convenient synthesis of the central core of helioporins, seco-pseudopterosins and pseudopterosins in racemic form is reported, using a Suzuki coupling (A-ring formation)-Friedel-Crafts acylation sequence, followed by synthetic elaboration of the resulting tetralone derivative. Key steps of the method are a totally diastereoselective cuprate conjugate addition and a final, spontaneous Friedel-Crafts acylation.

Solvent-dependent oxidations of 5- and 6-azaindoles to trioxopyrrolopyridines and functionalised azaindoles

A regioselective synthesis of 4,7-dimethoxy 5- and 6-azaindoles 2 has been achieved, based on the appropriate choice of ortho-directing or ortho-repulsing groups in the formylation of a pyridine ring. Studies on the regioselectivity of the formylation step and on the preparation of azidoacrylate intermediates 4 are described in this paper. The reactivity of the 5- and 6-azaindole structures towards BBr3-mediated selective monodemethylation and oxidative demethylation reactions were also investigated. The regioselectivity of the deprotection was confirmed using a chemical approach. Oxidation reactions were then carried out on either dimethoxy- or hydroxymethoxyazaindoles, in different solvents, using [bis(trifluoroacetoxy)iodo]benzene. In acetonitrile-water, trioxopyrrolopyridines 12 were obtained, whereas the formation of functionalised azaindoles 17 was observed in acetonitrile-methanol. The tautomeric structure of the trioxopyrrolopyridines was proved by X-ray diffraction analysis.

A mild, chemoselective oxidation of sulfides to sulfoxides using o-iodoxybenzoic acid and tetraethylammonium bromide as catalyst

A mild, selective, and high-yielding method for oxidation of sulfides to sulfoxides using IBX and tetraethylammonium bromide in a variety of solvents is described. The method offers the advantage of short reaction times, no over-oxidation to sulfones, and compatibility to a wide range of functional groups.

Polyvalent iodine in organic chemistry

Tricoordinate, I(III), and pentacoordinate, I(V), polyvalent iodine compounds have been known for over a century. In the last twenty years, new polyvalent iodine reagents have been introduced along with synthetic methodologies, based on these and derived reagents, that play an ever increasing role in contemporary organic chemistry. In this Perspective, an overview of these developments is provided with emphasis on the chemistry and uses of aryl-, alkenyl-, and alkynyliodonium salts in preparative and synthetic organic chemistry. It is hoped that this brief overview, along with recent more comprehensive reviews of the field, will stimulate further developments and applications of this useful class of compounds across a broad spectrum of organic chemistry.

Iodine(V) reagents in organic synthesis. Part 1. Synthesis of polycyclic heterocycles via Dess-Martin periodinane-mediated cascade cyclization: generality, scope, and mechanism of the reaction

The scope, generality, and mechanism of the Dess-Martin periodinane-mediated cyclization reaction of unsaturated anilides discovered during the total synthesis of the CP-molecules (phomoidrides A and B) are delineated. A plethora of heterocyclic compounds are accessible by employing gamma,delta-unsaturated amides (derived from anilines and carboxylic acids), urethanes, or ureas (derived from isocyanates and allylic alcohols and amines) as substrates. Optimization of the reaction led to room-temperature conditions, while isotope labeling studies allowed a mechanistic rationale for this cascade reaction.

Total synthesis of the CP-molecules (CP-263,114 and CP-225,917, phomoidrides B and A). 3. Completion and synthesis of advanced analogues

The completion of the total syntheses of the CP-molecules is reported. Several strategies and tactics, including the use of amide-based protecting groups for the homologated C-29 carboxylic acid and the use of an internal pyran protecting group scheme, are discussed. The endeavors leading to the design of new methods for the homologation of hindered aldehydes and to the isolation of a polycyclic byproduct (23), which inspired the development of a new series of reactions based on iodine(V) reagents, are described. In addition, the discovery and development of the LiOH-mediated conversion of CP-263,114 (1) to CP-225,917 (2) is described, and a mechanistic rationale is presented. Finally, a synthetic route to complex analogues of the CP-molecules harboring a maleimide moiety in place of the maleic anhydride is presented.

Iodine(V) reagents in organic synthesis. Part 2. Access to complex molecular architectures via Dess-Martin periodinane-generated o-imidoquinones

o-Imidoquinones, a rather rare class of compounds, are prepared from anilides by the action of Dess-Martin periodinane (DMP) and water. Their chemistry has been extensively investigated and found to lead to p-quinones and polycyclic systems of diverse molecular architectures. Applications of this methodology to the total synthesis of the naturally occurring compounds, epoxyquinomycin B and BE-10988, are described. Finally, another rare chemical entity, the ketohydroxyamide moiety, has been accessed through this DMP-based synthetic technology, and its reactivity has been studied. Among its most useful reactions is a set of cascade heterocyclic annulations leading to a variety of polycyclic systems of possible biological relevance.