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endo,endo ‐ and exo,exo ‐Bicyclo[1.1.0]butane‐2,4‐dimethanol Dimesylate: Synthesis, Structure and Solvolysis
Author(s) -
Bentley T. William,
Llewellyn Gareth,
Kottke Thomas,
Stalke Dietmar,
Cohrs Carsten,
Herberth Edith,
Kunz Ulrike,
Christl Manfred
Publication year - 2001
Publication title -
european journal of organic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.825
H-Index - 155
eISSN - 1099-0690
pISSN - 1434-193X
DOI - 10.1002/1099-0690(200104)2001:7<1279::aid-ejoc1279>3.0.co;2-9
Subject(s) - chemistry , solvolysis , heterolysis , butane , bicyclic molecule , stereochemistry , epimer , dissociation (chemistry) , acetone , methanol , medicinal chemistry , hydrolysis , organic chemistry , catalysis
The title compounds endo , endo ‐ 9 and exo , exo ‐ 9 were prepared from benzvalene. As determined by single‐crystal X‐ray diffraction, several geometrical parameters of endo , endo ‐ 9 are particularly remarkable, namely the large interflap angle of the bicyclo[1.1.0]butane system (128.2°) and the length of the C‐1−C‐3 bond (151.2 pm). Solvolyses of endo , endo ‐ 9 in 60% acetone/water, ethanol and 2,2,2‐trifluoroethanol gave rise mainly to cis ‐5‐substituted cyclopent‐2‐ene‐1‐methanol mesylates ( cis ‐ 10 , cis ‐ 11 ). Small quantities of the corresponding trans isomers ( trans ‐ 10, trans ‐ 11 ) suggest a configurational conversion of the intermediate, which is proposed to be the nonclassical pseudoaxial 2‐mesyloxymethyl‐substituted cyclopent‐3‐en‐1‐yl cation ( ax ‐ 31 ) formed from endo , endo ‐ 9 by heterolytic dissociation accompanied by a Wagner‐Meerwein rearrangement. The solvolyses of exo , exo ‐ 9 took an entirely different course and afforded nonrearranged products ( 26 , 27 ) exclusively. This is interpreted in terms of the stereochemical requirements of the Wagner−Meerwein rearrangement, which in the case of exo , exo ‐ 9 would result in a highly strained cation such as 32 or 33 . In consequence, the generation of the bicyclobutylcarbinyl cation 34 seems to be the most favourable alternative. This result, together with kinetic data for solvolyses of endo , endo ‐ 9 and exo , exo ‐ 9 , casts doubt on a report on solvolyses of the dimethylbicyclo[1.1.0]but‐2‐ylcarbinyl tosylates 6 .4 Solvolyses of endo , endo ‐ 9 in several solvents are about 5 times faster than those of the ditosylate 2 (or the corresponding dimesylate), a less flexible bicyclo[1.1.0]butane derivative. That the solvolysis of exo , exo ‐ 9 takes place about 8 times more slowly than endo , endo ‐ 9 is interpreted by invoking a weaker σ‐participation in the case of the former. In comparison to the stereochemically closely related exo , exo ‐ 9 , the cyclobutanedimethanol ditosylate 28 solvolyses only 50 times more slowly.