The Synthesis and Physical Properties of Some 1- and 2-Pyrazolines 1

The geometrically isomeric cis-and trans-3-methyl-4-ethyl-3-carbomethoxy-A~-pyrazolines were prepared and their pyrolysis and photolysis studied. The isomeric pyrazoli~les gave cyclopropane products of mixed stereochemistry, but predominantly with retention of the stereochemistry present in the starting pyrazoline. Each pyrazoline gave stereospecifically a different a,p-unsaturated ester product. This stereospecificity can be related to the structure of the pyrazoline through the requirement that the loss of nitrogen must be from the side of the pyrazoline that is trans to the hydrogen at C-4.

Section: Discussionsupporting

confidence: 82%

Section: Discussionmentioning

confidence: 99%

See 1 more Smart Citation

Pyrazolines. VII. Concerning the formation of olefins from the pyrolysis of pyrazolines

McGreer¹,

Wu²

1967

“…The regioselectivity of the cycloaddition reaction was clearly shown by the p.m.r. spectrum of the product 37, which showed that there was only one proton (multiplet at 7 5.11) adjacent to the -N=N-moiety (42 The synthesis of ( +)-sativene (3) was achieved via a sequence which was in the later steps very similar to the preparation of (-)-copacamphene (1). However, the required bicyclic diene 39 was prepared via a route quite different from that employed for the corresponding compound 22 in the copa series.…”

Section: Synthesis Of (-)-Cyclocopacamphene (2)mentioning

confidence: 99%

Stereoselective Total Synthesis of Copa and Ylango Sesquiterpenoids: (−)-Copacamphene, (−)-Cyclocopacamphene, (+)-Sativene, (+)-Cyclosativene

Piers¹,

Geraghty²,

Smillie³

et al. 1975

EDWARD PIERS, M. BERT GERAGHTY, R. DEAN SMILLIE, and MARCEL SOUCY. Can. J. Chem. 53,2849 (1975).Stereoselective total syntheses of the tricyclic sesquiterpenoids (-)-copacamphene (1) and (+)-sativene (3) and of the related tetracyclic compounds (-)-cyclocopacamphene (2) and (+)-cyclosativene (4) are described. An efficient four-step synthetic sequence was employed to convert the bicyclic dione 5 into the olefinic ketone 8. The latter compound was converted in four steps into the olefinic alcohol 23. Eliminative cyclization of the corresponding tosylate 25 gave (-)-copacamphene (1) in high yield. In similar fashion, (+)-sativene (3) was obtained by cyclization of the olefinic tosylate 42, which in turn was derived via a four-step synthetic sequence from the olefinic ketone 9. Oxidation of the olefinic alcohol 23 afforded the aldehyde 34. Conversion of the latter compound into the p-tosylhydrazone 35, followed by pyrolysis of the corresponding lithium salt 36, gave the pyrazoline 37. Photolysis of 37 afforded, in high yield, (-)-cyclocopacamphene (2). Similarly, (+)-cyclosativene (4) On decrit des syntheses totales et stCreos6lectives des sesquiterpenoides tricycliques (-) copacamphene (1)et (+) sativene (3)et des composCs t6tracycliques (-) cyclocopacamphene (2) et (+) cyclosativtne (4) qui leur sont relies. On a utilise une sequence de synthtse efficace impliquant 4 Btapes pour transformer la dione 5 en cetone non-saturee 8. On a converti ce dernier compose en alcool olefinique 23 en quatre etapes. L'elimination cyclisante du tosylate correspondant 25 donne le (-) copacamphtne (1) avec un bon rendement. D e la mCme maniere, on obtient le (+) sativene (3) par cyclisation du tosylate non-sature 42, qui derive de la cetone non-saturk 9 par I'intermediaire d'une sequence de synthese en 4 etapes. L'oxydation de I'alcool insature 23 fournit l'aldehyde 34 qui est transforme en p-tosylhydrazone 35. La pyrolyse du sel de lithium de cette derniere (36) donne la pyrazoline 37 qui par photolyse conduit, avec un bon rendement, au (-) cyclocopacamphtne (2). On obtient le (+) cyclosativene (4) de la mCme maniere a partir de I'alcool 41 par I'intermediaire de la pyrazoline 46.

“…In earlier work it has been suggested that both carbon-nitrogen bonds are being cleaved in the rate-determining step of 1-pyrazoline thermolysis, and that a nitrogen free intermediate is produced (4). This interpretation arose from a progressive decrease in activation energy on going from 1-pyrazoline (1) to 3,3,5,5-tetramethyl-1-pyrazoline (2).…”

mentioning

confidence: 99%

Secondary deuterium kinetic isotope effects on the thermolysis of 1-pyrazolines

Al-Sader¹,

Crawford²

1968

Self Cite

Secondary kinetic isotope effects on four deuterated 1-pyrazolines support the formation of a trimethylene intermediate during gas phase thermolysis. Calculation of cyclization relative rate constants for the trimethylene intermediates reveals that substitution of hydrogen by deuterium has no effect when the terminal methylenes are substituted, but the rateconstants are decreased when thecentral methylene's hydrogens are substituted. Explanations are advanced for all of the observed effects.