Ring-Closing Metathesis Reactions of Bis(enynes): Selectivity and Surprises

A study of the ring-closing metathesis reactions of two bis­(enynes) is presented. These substrates, which contain two alkenes and two alkynes, as well as a resident stereocenter, can potentially generate metathesis products resulting from many reaction pathways. In this contribution we present our results on these reactions, show how small changes in reaction conditions can lead to different product ratios, and attempt to provide a rationale for the outcomes

Phosphine-Catalyzed Cycloadditions of Allenic Ketones: New Substrates for Nucleophilic Catalysis

A range of phosphine-catalyzed cycloaddition reactions of allenic ketones have been studied, extending the scope of these processes from the more widely used 2,3-butadienoates to allow access to a number of synthetically useful products. Reaction of allenyl methyl ketone 4 with exo-enones afforded spirocyclic compounds in good regioselectivity and promising enantioselectivity via a [2 + 3] cycloaddtion. Aromatic allenyl ketones undergo a phosphine-promoted dimerization to afford functionalized pyrans, leading to a formal [2 + 4] Diels−Alder product, but did not react in the [2 + 3] cycloaddition. The results from other reactions that had found utility with 2,3-butadienoates are also reported

Phosphine-Catalyzed Cycloadditions of Allenic Ketones: New Substrates for Nucleophilic Catalysis

A range of phosphine-catalyzed cycloaddition reactions of allenic ketones have been studied, extending the scope of these processes from the more widely used 2,3-butadienoates to allow access to a number of synthetically useful products. Reaction of allenyl methyl ketone 4 with exo-enones afforded spirocyclic compounds in good regioselectivity and promising enantioselectivity via a [2 + 3] cycloaddtion. Aromatic allenyl ketones undergo a phosphine-promoted dimerization to afford functionalized pyrans, leading to a formal [2 + 4] Diels−Alder product, but did not react in the [2 + 3] cycloaddition. The results from other reactions that had found utility with 2,3-butadienoates are also reported

Practical Synthesis of Sultams via Sulfonamide Dianion Alkylation: Application to the Synthesis of Chiral Sultams

A practical synthesis of sultams was developed via intramolecular sulfonamide dianion alkylation. This method has been applied toward the synthesis of chiral sultams, which are synthetically valuable as chiral auxiliaries

New Method for the Synthesis of Diversely Functionalized Imidazoles from N-Acylated α-Aminonitriles

A new general method for the synthesis of medicinally important diversely functionalized imidazoles from N-acylated α-aminonitriles has been developed. N-Acylated α-aminonitriles were reacted with triphenylphosphine and carbon tetrahalide to afford 2,4-disubstituted 5-halo-1H-imidazoles in good yield. This new methodology was applied for the synthesis of 2-butyl-4-chloro-5-hydroxymethylimidazole. These halo-imidazoles can be directly converted to 2,4,5-trisubstituted imidazoles through palladium-catalyzed coupling reactions

Practical Synthesis of Functionalized 1,5-Disubstituted 1,2,4-Triazole Derivatives

A general approach for the synthesis of 1,5-disubstituted-1,2,4-triazole compounds is described. A series of new oxamide-derived amidine reagents can be accessed in excellent yield with minimal purification necessary. Typically, these amidine reagents are stable crystalline solids and in certain cases were found to exist in a cyclic form as determined by NMR spectroscopy. Under optimized conditions, the direct reaction of these prepared reagents with various hydrazine hydrochloride salts efficiently generates the target triazoles. Both aromatic and aliphatic hydrazines react readily with the amidine reagents under very mild reaction conditions, delivering desired 1,5-disubstituted-1,2,4-triazole derivatives in good yields

Highly Enantioselective Hydrogenation of Aromatic-Heteroaromatic Ketones

Asymmetric hydrogenation of ketone 1 using trans-RuCl2[(R)-xylbinap][(R)-daipen] (3) as a catalyst afforded secondary alcohol 2 quantitatively and in 99.4% ee. Further exploration of the effect of the thiazole ring substitution revealed that the catalyst was highly effective for the enantioselective hydrogenation of 5-benzoyl thiazoles, which afforded corresponding alcohols in 92−99% ee. The same protocol was applicable to a variety of aromatic-heteroaromatic ketones to generate secondary alcohols in excellent enantioselectivities

Preparation of C-3,5-Acyl Furanoses via Highly Selective Intramolecular Acyl Migration

A practical synthesis of C-3,5-acyl furanose via a base-catalyzed, highly selective intramolecular acyl migration in alcohol solvents is reported

Preparation of C-3,5-Acyl Furanoses via Highly Selective Intramolecular Acyl Migration

A practical synthesis of C-3,5-acyl furanose via a base-catalyzed, highly selective intramolecular acyl migration in alcohol solvents is reported

Novel Intramolecular Reactivity of Oximes: Synthesis of Cyclic and Spiro-Fused Imines

Under conventional heat (135−145 °C) or microwave irradiation and 1 equiv of acetic anhydride, ortho-substituted aryl-oximes undergo a novel sp3 C−H activated cyclization to produce the corresponding isoindoles, and aliphatic oximes afford the corresponding dihydropyrroles. The cyclization occurs with various substrates in good yield (46−82%) leading to unique spiro-fused and cyclic imines. An initial mechanistic investigation suggests the reaction occurs via a nitrenium or vinyl nitrene intermediate