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Stereoselektive Bildung von Oxaspiropentanen und Spiropentylketonen. Zur Stereochemie der nucleophilen Substitution am Cyclopropan
Author(s) -
Seebach Dieter,
Dammann Reinhard,
Lindner Hans Jörg,
Kitschke Brigitte
Publication year - 1979
Publication title -
helvetica chimica acta
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.74
H-Index - 82
eISSN - 1522-2675
pISSN - 0018-019X
DOI - 10.1002/hlca.19790620424
Subject(s) - chemistry , cyclopropane , stereochemistry , epoxide , nucleophilic substitution , intramolecular force , ring (chemistry) , substitution reaction , stereoselectivity , crystallography , medicinal chemistry , catalysis , organic chemistry
Stereoselective Formation of Oxaspiropentanes and of Spiropentyl Ketones. On the Stereochemistry of Nucleophilic Substitution at Cyclopropanes In an intramolecular S N 2‐type substitution with formation of the spiro[2.2]‐pentane skeleton, the highly strained transition state 2 with one three membered ring in an equatorial/equatorial and one in an apical/equatorial position of a pentacoordinated carbon atom ought to be ‐ at least formally ‐ involved. Yet, several examples of such processes are known. With the endo/exo isomeric bromohydrines 4 and 5 and bromoketones 13 and 14 this reaction is now shown to occur with clean inversion of configuration at the cyclopropane carbon atom. Unambiguous configurational assignments are made by X‐ray crystal structure determinations of the 7′ exo ‐bromo‐benzoate 6 (from the bromohydrine 4 ), of the endo ‐sulfonate 12 (from oxaspiropentane 7 , formed from 4 ), of the 7 exo ‐bromonorcarane 13 , and of its cyclization product 15 . ‐ A comparison of the qualitatively measured rates of epoxide ring formation from the closely related systems 18 and 20 proves the expected slower substitution at the cyclopropane carbon atom as compared to the open chain analogue.