1,3‐Dipolar Cycloadditions of a 2‐Oxoethanenitrile Oxide Derived from (2R)‐Bornane‐10,2‐sultam to Electronically Modified 4,4′‐Disubstituted Stilbenes

2009/06/01 by Jan Romanski, J. Romański, Christian Chapuis +1 · 1 citation
Chemistry · Pharmacology, Toxicology and Pharmaceutics · #Organic Chemistry Cycloaddition Reactions #Fluorine in Organic Chemistry #Asymmetric Synthesis and Catalysis

paper · doi:10.1002/hlca.200800412

Abstract

Abstract magnified image Thanks to its type‐II dipole nature, we were able to demonstrate the higher reactivity of the SO 2 /CO syn ‐conformer for the uncatalyzed 1,3‐dipolar cycloaddition of the 2‐oxoethanenitrile oxide 2 derived from bornane‐10,2‐sultam to the symmetric 4,4′‐disubstituted trans ‐stilbenes 3a – 3i . The C( α )‐ si dipolarophile π y approach along the CO bond precludes the use of the steric rules formerly expressed for this pseudo‐ C 2 ‐symmetric auxiliary. The observed diastereoselectivity is related to the electronic nature of the dipolarophile and may be predicted on the basis of its σ para Hammett constant. The absolute configuration was based on the X‐ray structure analysis of cycloadduct (4 S ,5 S )‐ 4b , which exhibits an SO 2 /CO anti ‐conformation. Finally, the results obtained with cis ‐stilbene suggest a nonsynchronous mechanism.

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