Diels-Alder based syntheses, applications

The synthesis of secondary amines from azides is efficient in terms of chemos-electivity [57] and has found valuable applications in the preparation of diamines [58,59], m-alkylaminoboronic esters [60], and in Diels-Alder-based amination reactions [61]. A convenient general route to open-chain polyamines, which play major roles in cellular differentiation and proliferation, has also been developed using the reductive alkylation of aliphatic aminoazides by (co-halogenoalk-yi)dichloroboranes as a key step [62] (Scheme 21). 

Tran orm-based or long-range strategies The retrosynthetic analysis is directed toward the application of powerful synthesis transforms. Functional groups are introduced into the target compound in order to establish the retion of a certain goal transform (e.g., the transform for the Diels-Alder reaction, Robinson annulation, Birch reduction, halolactonization, etc.). 

Development of base-catalyzed Diels-Alder reaction of 3-hydroxy-2-pyrone and its application to synthesis of bioactive compounds 99YGK84. 

Organic syntheses based on biosynthetic proposals are often extremely concise and elegant.6 Although the constitution and stereochemical complexity of carpanone may seem formidable, the sequential application of the Diels-Alder and oxidative phenolic coupling transforms7 to the natural product provides an exceedingly efficient solution. Chapman s striking synthesis of carpanone typi-... 

Okamura H., Iwagawa M. and Nakatani M. Development of Base Catalyzed Diels-Alder Reaction of 3-Hydroxy-2-Pyrone and Application to Synthesis of Biologically Active Compounds Org. Chem. Japan 1999 57 84... 

This procedure describes the preparation and application of an effective chiral catalyst for the enantioselective Diels-Alder reaction.11 The catalyst is derived from optically active 1,2-diphenylethylenediamine, the preparation of which (either antipode) was described in the preceding procedure. The aluminum-based Lewis acid also catalyzes the cycloaddition of crotonoyl oxazolidinones with cyclopentadiene,11 and acryloyl derivatives with benzyloxymethylene-cyclopentadiene. The latter reaction leads to optically pure intermediates for synthesis of prostaglandins.11... 

In the late 1970s, Kirchhoff at Dow Chemical Company developed the use of benzocyclobutenes in polymer synthesis and modification. These efforts culminated in 1985 with the issuance of the first patent describing the use of benzocyclobutene in the synthesis of high-molecular-weight polymer.27 Similar work that involved a thermosetting system based on Diels-Alder cycloaddition between terminal benzocyclobutene and alkyne groups,28,29 was reported separately and independently by Tan and Arnold.28 Since these initial discoveries, the field of benzocyclobutene polymers has expanded rapidly and benzocyclobutene chemistry constitutes the basis of a new and versatile approach to the synthesis of high-performance polymers for applications in the electronics and aerospace industries.30... 

The use of porphyrinic ligands in polymeric systems allows their unique physio-chemical features to be integrated into two (2D)- or three-dimensional (3D) structures. As such, porphyrin or pc macrocycles have been extensively used to prepare polymers, usually via a radical polymerization reaction (85,86) and more recently via iterative Diels-Alder reactions (87-89). The resulting polymers have interesting materials and biological applications. For example, certain pc-based polymers have higher intrinsic conductivities and better catalytic activity than their parent monomers (90-92). The first example of a /jz-based polymer was reported in 1999 by Montalban et al. (36). These polymers were prepared by a ROMP of a norbor-nadiene substituted pz (Scheme 7, 34). This pz was the first example of polymerization of a porphyrinic macrocycle by a ROMP reaction, and it represents a new general route for the synthesis of polymeric porphyrinic-type macrocycles. 

Following the first reports in the literature of catalytic imprinted beads, a number of authors also reported applications of this polymer format to several imprinting systems. Busi et al. [64] reported the preparation of catalytic active beads for the Diels-Alder reaction using a TSA as a template. Jakubiak and co-workers developed imprinted beads for the oxidation of phenols based on a Cu(II) complex as catalytic centre [65]. Say and collaborators described the synthesis of microbeads also based on a Cu(II) complex with esterase activity towards paraoxon (60), a potent nerve agent [66]. The imprinted beads enhanced the rate of reaction over the non-imprinted polymer by a factor of 40, as resulted from the ratio of the corresponding kciil. 

Asymmetric Diels-Alder reaction and its applications based on catalysis by bis(oxa-zoline)copper(II) complexes have been published in full details. This method has been further extended to the synthesis of 2,3-dihydropyran-6-ylphosphonates, 4-aminodihy-dropyrans, and piperidones. Note that both epimeric amines are accessible by merely changing the diene substrate, that is, ( )- versus (Z)-configuration. Diazolidi-none 75 serves as a chiral catalyst that also activates enals (actual dienophiles being the iminium ions)." ... 

Progress in Heterocyclic Chemistry (PHC) Volume 7 reviews critically the heterocyclic literature published mainly in 1994. The first two chapters are traditionally review articles. Chapter 1 surveys useful synthetic routes to "Polyfunctional Pyrroles and Pyrazoles" starting from conjugated azoalkenes. This review is based on the researches of O. A. Attanasi and his school in Urbino (Italy). As last year the second review is unconventional, comprising a compilation of the" Application of Diels-Alder Cycloaddition Chemistry for Heterocyclic Synthesis". It is written by our president A. Padwa and is in an unusual format with a pertinent list of references dating back forty years in some cases. We were encouraged to include this review because of favourable comments received from readers about this type of survey in PHC Volume 6. 

Several reviews have been published within the year which are of general relevance to the photoreactions of aromatic compounds. The subjects of these reviews include photochemistry in ionic liquids and in isotropic and anisotropic media, organic synthesis utilizing photoinduced electron-transfer reactions," heteroatom-directed photoarylation processes, photochromism, and photochemical molecular devices. Reviews more directly pertinent to the sections in the present chapter include those of the photoisomerization of five-membered heteroaromatic azoles, the photocycloaddition of benzene derivatives to alkenes, Diels-Alder additions of anthracenes, advances in the synthesis of polycyclic aromatic compounds, diarylethene-based photochromic switches, the photo-Fries rearrangement, and the application of Diels-Alder trapping of photogenerated o-xylenols to the synthesis of novel compounds. " A number of chapters in the two recently published handbooks of photochemistry and photobiology and in the revised edition of the text on photochromism are also pertinent to the current subject matter. 

The presented review describes total syntheses directed towards 6-amino-6,8-dideoxy-D-eryt/iro-D-galacto-octose, commonly named lincosamine - the sugar component of the antibiotic lincomycin. In the first part we present total syntheses of lincosamine that start from carbohydrate precursors. The D-galactose-derived aldehyde is the most frequently used synthon. In the second part, total syntheses of lincosamine from non-carbohydrate precursors are presented. This part of the review is divided into two subsections. The first one groups syntheses based on the application of furan compounds. In the second one we present a hetero-Diels-Alder approach to the synthesis of lincosamine. 

The methodology based on nitroso DieIs-alder reaction that proved useful in the synthesis of tropane alkaloids also seemed to open an attractive route to some other alkaloids. Compared to the intramolecular imino Diels-Alder reaction (ref. Ic) the intramolecular variant of the nitroso Diels-Alder reaction has received far less attention (refs. 6b 12), despite the enormous potential it holds for alkaloid synthesis. With this in mind we proceeded to examine the application of the intramolecular nitroso Diels-Alder cycloaddition in the synthesis of alkaloids possessing saturated nitrogen heterocyclic ring systems. 

The Bode group have documented an NHC-catalyzed enantioselective synthesis of ester enolate equivalents with a,p-unsaturated aldehydes as starting materials and their application in inverse electron demand Diels-Alder reactions with enones. Remarkably, the use of weak amine bases was crucial DMAP (conjugate acid = 9.2) andN-methyl morpholine (NMM, conjugate acid pAa = 7.4) gave the best results. A change in the co-catalytic amine base employed in these reactions could completely shift the reaction pathway to the hetero-Diels-Alder reaction, which proceeded via a catalytically generated enolate. An alternative pathway that occurred via a formal homoenolate equivalent was therefore excluded. It is demonstrated that electron-rich imidazolium-derived catalysts favor the homoenolate pathways, whereas tri-azolium-derived structures enhance protonation and lead to the enolate and activated carboxylates (Scheme 7.71). 

Enantioselective vanadium and niobium catalysts provide chemists with new and powerful tools for the efficient preparation of optically active molecules. Over the past few decades, the use of vanadium and niobium catalysts has been extended to a variety of different and complementaiy asymmetric reactions. These reactions include cyanide additions, oxidative coupling of 2-naphthols, Friedel-Crafts-type reactions, pinacol couplings, Diels-Alder reactions, Mannich-type reactions, desymmetrisation of epoxides and aziridines, hydroaminations, hydroaminoalkylations, sulfoxida-tions, epoxidations, and oxidation of a-hydroxy carbo) lates Thus, their major applications are in Lewis acid-based chemistiy and redox chemistry. In particular, vanadium is attractive as a metal catalyst in organic synthesis because of its natural abundance as well as its relatively low toxicity and moisture sensitivity compared with other metals. The fact that vanadium is present in nature in equal abundance to zinc (albeit in a more widely distributed form and more difficult to access) is not widely appreciated. Inspired by the activation of substrates in nature [e.g. bromoperoxidase. 

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