Intra- and Intermolecular Hydrogen Bonding Effects in Cycloadditions between Nitrile Oxides and 4-Benzoylamino-2-cyclopenten-1-ol and Its Derivatives

Abstract

Keywords: Cycloadditions / Nitrile oxides / Nitroso compounds / Solvent effects / StereoselectivityCycloadditions between nitrile oxides and cis-4-benzoylamino-2-cyclopenten-1-ol offer an example in which a strong intramolecular hydrogen bond completely offsets the syn-directing ability of the cyclopentene substituents. Solvents affected the conformational equilibrium of the cyclopentene dipolarophile but did not sizeably influence the cycloaddition selectivity, showing the absence of directing effects between

N,O-Nucleosides from Ene Reactions of Nitrosocarbonyl Intermediates with the 3-Methyl-2-buten-1-ol

“…Recently, we have proposed the synthesis of a new class of carbocyclic nucleosides starting from cyclopentadiene using the nitrosocarbonyl intermediates (RCONO, 1 ) chemistry . These intermediates, generated by the mild oxidation of nitrile oxides with tertiary amine N -oxides or by oxidation of hydroxamic acids, are efficiently trapped by cyclopentadiene (Scheme ) to afford the hetero Diels–Alder (HDA) cycloadducts 2 that are highly reactivity dipolarophiles and were employed to synthesize the conformationally restricted carbocyclic moiety aminols 4 through amide hydrolysis and N–O bond cleavage of the cycloadducts 3 . Aminols 4 were useful for the linear construction of purine and pyrimidine nucleosides 5 .…”

Enantioselective Photocycloaddition Mediated by Chiral Brønsted Acids: Asymmetric Synthesis of the Rocaglamides

“…Using the optimized conditions for enantioselective photocycloaddition (entry 11), we achieved the synthesis of the natural products rocaglaol 9 and rocaglamide 10 1c (Scheme ). By using 4 as dipolarophile and 7g as additive, we obtained rocaglaol 9 in 96% ee after decarboxylation and reduction of intermediate 11 …”

“…The TADDOL complexing agent could be recovered in high yield by precipitation from methanol. A control experiment involving addition of 7f and 5 equiv of methanol (entry 10) led to a loss of enantioselectivity presumably due to achiral background reactions promoted by the protic cosolvent …”

Generation and Trapping of Nitrosocarbonyl Intermediates

“…The benzhydroxymoyl chloride 283 was treated with triethylamine and NMO in the presence of freshly distilled cyclopentadiene to afford the HDA cycloadduct 56 in 68% yield (Scheme ). the same procedure was followed for large-scale preparation of the HDA cycloadduct which served for the synthetic elaboration into several structures, including carbocyclic nucleosides and biomimetic compounds. − …”