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Transannular Ring Expansion in Electrophilic Reactions of Spirocyclopropane‐Substituted Norbornene and Its Oxirane and Azirane Derivatives
Author(s) -
Adam Waldemar,
Carballeira Nestor,
Crämer Elisabeth,
Peters EvaMaria,
Peters Karl,
Schnering Hans Georg Von
Publication year - 1987
Publication title -
chemische berichte
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.667
H-Index - 136
eISSN - 1099-0682
pISSN - 0009-2940
DOI - 10.1002/cber.19871200411
Subject(s) - chemistry , adduct , electrophile , trifluoroacetic acid , moiety , oxetane , ring (chemistry) , hydrolysis , diol , nucleophile , stereochemistry , medicinal chemistry , organic chemistry , catalysis
Abstract The spironorbornene N gave on treatment with toluenesulfenyl chloride as minor product the 1,2‐adduct N‐1a and as major products the disubstituted brendanes N‐2a,b . The dispironorbornene D gave trace amounts of the 1,2‐adduct D‐1a and essentially exclusively the skeletally rearranged disubstituted brendane D‐2a . On the other hand, the oxirane O led on treatment with trifluoroacetic acid to the hydroxy esters O‐2a,b which were hydrolyzed to give the respective diols O‐2c,d , while the azirane A afforded the amino esters A‐2a,b , which were hydrolyzed to yield the respective amino alcohols A‐2c,d . Neither for the oxirane nor for the azirane were 1,2‐adducts observed in these acidcatalyzed reactions. The 2,6‐disubstituted brendanes (minor products) were formed via direct transannular ring expansion of the spirocyclopropane moiety in the bridged cations 3 that result from electrophilic attack on the norbornenes. Alternatively, the bridged cations 3 first underwent skeletal rearrangement and subsequent transannular ring expansion led to the 3,8‐disubstituted brendanes (major products). X‐ray analysis was essential to elucidate rigorously the structures of the sulfones N‐1b and N‐2c and the 3,8‐diol O‐2d .