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Natural products have routinely been used both as sources of and inspiration for new crop protection active ingredients. The natural product UK-2A has potent anti-fungal activity but lacks key attributes for field translation. Post-fermentation conversion of UK-2A to fenpicoxamid resulted in an active ingredient with a new target site of action for cereal and banana pathogens. Here we demonstrate the creation of a synthetic variant of fenpicoxamid via identification of the structural elements of UK-2A that are needed for anti-fungal activity. Florylpicoxamid is a non-macrocyclic active ingredient bearing two fewer stereocenters than fenpicoxamid, controls a broad spectrum of fungal diseases at low use rates and has a concise, scalable route which is aligned with green chemistry principles. The development of florylpicoxamid represents the first example of using a stepwise deconstruction of a macrocyclic natural product to design a fully synthetic crop protection active ingredient.

The natural product UK-2A was transformed postfermentation to fenpicoxamid (InatreqTM active), a new crop protection active ingredient for disease control in wheat and bananas. A second-generation molecule inspired by UK-2A necessitates a nonmacrocyclic structure with fewer stereogenic centers to enable cost-effective large-scale production via total synthesis. Deconstruction of the UK-2A macrocycle led to the identification of key structural elements necessary to provide effective control of disease. Beginning with a nonmacrocyclic fragment containing these structural elements, a new molecule was created using structure–activity relationship studies focused on improving control of wheat leaf blotch caused by Zymoseptoria tritici. These studies led to the discovery of florylpicoxamid (AdaveltTM active), a new active ingredient in the picolinamide class of fungicide chemistry.

We describe here details of our investigations into Pd-catalyzed and thermal aza-Claisen-carbocyclizations of N-allyl ynamides to prepare a variety of α,β-unsaturated cyclopentenimines. The nature of the ynamide electron-withdrawing group and β-substituent plays critical roles in the success of this tandem cascade. With N-sulfonyl ynamides, the use of palladium catalysis is required, as facile 1,3-sulfonyl shifts dominate under thermal conditions. However, since no analogous 1,3-phosphoryl shift is operational, N-phosphoryl ynamides could be used to prepare similar cyclopentenimines under thermal conditions through zwitter ionic intermediates that undergo N-promoted H-shifts. Alternatively, by employing ynamides bearing tethered carbon nucleophiles, the zwitter ionic intermediates could be intercepted, giving rise rapidly to more complex fused bi- and tricyclic scaffolds.

Efforts in developing an expeditious and convenient method for synthesizing γ–amino-ynamides via nucleophilic addition of lithiated ynamides to aryl imines are described. This work also features an aza-variant of a Meyer-Schuster rearrangement of γ–amino-ynamides and the synthetic utility of γ–amino-ynamides in an intramolecular ketenimine-[2 + 2] cycloaddition.

We describe here the first synthesis of N-phosphoryl ynamides featuring C- and P-chirality via copper(I)-catalyzed amidative cross-couplings between phosphoramidates and phosphordiamidates with alkynyl bromides. Also featured is a tandem aza-Claisen-hetero-[2+2] cycloaddition for the synthesis of N-phosphoryl azetidin-2-imines.

A novel thermal 3-aza-Claisen rearrangement of N-allyl ynamides for the synthesis of α-allyl imidates is described. Also, a sequential aza-Claisen, Pd-catalyzed Overman rearrangement is described for the synthesis of azapine-2-ones.

An Overview on Ynamines Alkynes represent one of the most important and versatile building blocks in organic synthesis. Heteroatom-substituted alkynes, which can be considered as subgroups of alkynes, have also been vastly utilized in developing synthetic methods. In particular, ynamines [1-amino-alkynes or N-alkynyl amines] became the most valuable subgroup of alkynes after the establishment of their practical synthesis in the 1960's. The first attempt at preparation of an ynamine was reported by Bode1,2 in 1892. While well-characterized ynamines were reported in 19583 and 1960,4 a practical synthesis was not achieved until the effort led by Viehe5 in 1963 in addition to other subsequent works. In the ensuing twenty years, the synthetic significance of ynamines in organic and organometallic chemistry was firmly established by the work of many creative synthetic chemists. These elegant pioneer works have been informatively and carefully reviewed by Viehe in 19676 and 1969;7 Ficini in 1976;8 Pitacco and Valentin9 in 1979; Collard-Motte and Janousek10 in 1986; Himbert11 in 1993; and most recently by us12,13 and Katritzky14. Open in a separate window The synthetic eminence of ynamines is well merited because of the predicable regioselectivity in their transformations as shown by the generalization in Scheme i, and more importantly, because they are inherently highly reactive. However, this latter attribute is also the source of the limitation that has seriously hampered the development of ynamine chemistry, thereby shortening the period of its prominence in synthesis. Ynamines are very sensitive toward hydrolysis, as protonation of the electron-rich alkynyl motif affords reactive keteniminium intermediates, which upon trapping with water leads to simple amides in a rather expensive manner (Scheme i). This hydrolytic instability has caused much difficulty in the experimental preparation and general handling of ynamines, and more detrimentally, rendered ynamine chemistry inaccessible. Open in a separate window Scheme i Consequently, the synthetic utility of ynamines has suffered a dramatic decline during the last thirty years.15 The most glaring limitations have been in the development of intramolecular and stereoselective reactions.7–14 The only reported intramolecular reaction of ynamines was Genet and Kahn's acid catalyzed addition of a hydroxyl group to an ynamine [i→ii in Scheme ii] in 1980,16 and although clever, it constitutes a hydrolytic process. Open in a separate window Scheme ii Besides Reinhoudt's17 sole account in 1987 reporting hetero-[4 + 2] cycloadditions of chiral ynamine iii with nitroalkenes that led to cycloadducts iv in modest de, the only other notable studies were reported ten years later by Fischer18 showcasing [2 + 2] cycloadditions of chiral ynamides v and vi with vinylidene chromium carbene complexes, and another three years later by Pericas19 in their Pauson-Khand cycloadditions using chiral ynamines vii.

A de novo transformation of N-allyl-N-sulfonyl ynamides to amidines is described featuring a palladium-catalyzed N-to-C allyl transfer via ynamido-palladium-pi-allyl complexes.

We describe here details of our investigations into Pd-catalyzed and thermal aza-Claisen–carbocyclizations of N-allyl ynamides to prepare a variety of α,β-unsaturated cyclopentenimines. The nature of the ynamide electron-withdrawing group and β-substituent plays critical roles in the success of this tandem cascade. With N-sulfonyl ynamides, the use of palladium catalysis is required, as facile 1,3-sulfonyl shifts dominate under thermal conditions. However, since no analogous 1,3-phosphoryl shift is operational, N-phosphoryl ynamides could be used to prepare similar cyclopentenimines under thermal conditions through zwitter ionic intermediates that undergo N-promoted H-shifts. Alternatively, by employing ynamides bearing tethered carbon nucleophiles, the zwitter ionic intermediates could be intercepted, giving rise rapidly to more complex fused bi- and tricyclic scaffolds.

Treatment of N-allyl-ynamides of type (I), (IV), (IX), and (XI) with Pd(PPh3)4 results in formation of bridged or fused bicycloimines depending on the alkene substitution.

A cascade of Pd-catalyzed N-to-C allyl transfer–intramolecular ketenimine–[2 + 2] cycloadditions of N-allyl ynamides is described. This tandem sequence is highly stereoselective and the [2 + 2] cycloaddition could be rendered in a crossed or fused manner depending on alkene substitutions, leading to bridged and fused bicycloimines.

A series of carbocyclization cascades of allyl ketenimines initiated through a thermal aza-Claisen rearrangement of N-phosphoryl-N-allyl ynamides is described. Interceptions of the cationic intermediate via Meerwein–Wagner rearrangements and polyene-type cyclizations en route to fused bi- and tricyclic frameworks are featured.

We describe here the first synthesis of N-phosphoryl ynamides featuring C- and P-chirality via copper(I)-catalyzed amidative cross-couplings between phosphoramidates and phosphordiamidates with alkynyl bromides. Also featured is a tandem aza-Claisen-hetero-[2+2] cycloaddition for the synthesis of N-phosphoryl azetidin-2-imines.

The Pd-catalyzed or thermally-induced treatment of ynamides of type (I) with amines allows convenient access to amidines.

A detailed study of amidine synthesis from N-allyl-N-sulfonyl ynamides is described here. Mechanistically, this is a fascinating reaction consisting of diverging pathways that could lead to deallylation or allyl transfer depending upon the oxidation state of palladium catalysts, the nucleophilicity of amines, and the nature of the ligands. It essentially constitutes a Pd(0)-catalyzed aza-Claisen rearrangement of N-allyl ynamides, which can also be accomplished thermally. An observation of N-to-C 1,3-sulfonyl shift was made when examining these aza-Claisen rearrangements thermally. This represents a useful approach to nitrile synthesis. While attempts to render this 1,3-sulfonyl shift stereoselective failed, we uncovered another set of tandem sigmatropic rearrangements, leading to vinyl imidate formation. Collectively, this work showcases the rich array of chemistry one can discover using these ynamides.

A novel thermal 3-aza-Claisen rearrangement of N-allyl ynamides for the synthesis of α-allyl imidates is described. Also, a sequential aza-Claisen, Pd-catalyzed Overman rearrangement is described for the synthesis of azapine-2-ones.

The reaction with α,β-unsaturated ketones is optimized and can be catalyzed by a combination of CuCl2 and AgSbF6.

The Ficini [2 + 2] cycloaddition using N-sulfonyl-substituted ynamides is described, featuring the utility of CuCl(2) and AgSbF(6) as catalysts. This work represents the first successful example of ynamides participating in a thermal [2 + 2] cycloaddition with enones.

A detailed account of Simmons-Smith cyclopropanations of allenamides en route to amido-spiro[2.2]pentanes is described here. While the diastereoselectivity was low when using unsubstituted allenamides, the reaction is overall efficient and general, representing the most direct synthesis of both chemically and biologically interesting amido-spiro[2.2]pentane systems. With alpha-substituted allenamides, while the diastereoselectivity could be improved significantly based on a series of conformational analyses, both mono- and bis-cyclopropanation products were observed. Consequently, several structurally intriguing amido-methylene cyclopropanes could also be prepared.

A de novo transformation of N-allyl-N-sulfonyl ynamides to amidines is described featuring a palladium-catalyzed N-to-C allyl transfer via ynamido-palladium-π-allyl complexes.

Direct arylation of the exocyclic amino groups of nucleosides represents a simple approach to N-aryl nucleoside derivatives. To date, one limitation has been that only electron-deficient aryl bromides and triflates possessed adequate reactivity for efficient, direct N-arylation of nucleosides. We demonstrate herein that Pd-Xantphos catalytic systems lead to successful N-arylation of suitably protected 2'-deoxyadenosine and 2'-deoxyguanosine with a wide range of aryl bromides.