“…The acetate could be further purified by flash column chromatography on silica gel ( R f = 0.47; ether:pentane 1:8). The NMR spectrum agreed with that reported in the literature …”
The stereochemistry of the deamination of (−)-spiropentylamine in acetic acid has been studied,
and it was found that one of the major products, (−)-spiropentyl acetate, was formed with essentially
complete inversion of configuration. This suggests that it is formed via an SN2 displacement on the
spiropentyldiazonium ion. The stereochemistry was established by the conversion of (−)-spiropentanecarboxylic acid to (−)-spiropentylamine via a Curtius rearrangement that proceeds with
retention of configuration. The (−) acid also was converted to spiropentyl methyl ketone with
methyllithium and then to (+)-spiropentyl acetate via the Baeyer−Villiger reaction that also results
in retention of configuration. The deamination of N-nitroso-N-spiropentyl urea was studied in
methanol, and spiropentyl methyl ether was a major product. Similarly, the reaction in water led
to spiropentanol. The latter reactions also lead to 2-methoxymethyl- or 2-hydroxymethyl-1,3-butadiene, respectively, corresponding to the alternative mode of reaction via a cyclopropyl cation−allyl cation rearrangement.
“…The acetate could be further purified by flash column chromatography on silica gel ( R f = 0.47; ether:pentane 1:8). The NMR spectrum agreed with that reported in the literature …”
The stereochemistry of the deamination of (−)-spiropentylamine in acetic acid has been studied,
and it was found that one of the major products, (−)-spiropentyl acetate, was formed with essentially
complete inversion of configuration. This suggests that it is formed via an SN2 displacement on the
spiropentyldiazonium ion. The stereochemistry was established by the conversion of (−)-spiropentanecarboxylic acid to (−)-spiropentylamine via a Curtius rearrangement that proceeds with
retention of configuration. The (−) acid also was converted to spiropentyl methyl ketone with
methyllithium and then to (+)-spiropentyl acetate via the Baeyer−Villiger reaction that also results
in retention of configuration. The deamination of N-nitroso-N-spiropentyl urea was studied in
methanol, and spiropentyl methyl ether was a major product. Similarly, the reaction in water led
to spiropentanol. The latter reactions also lead to 2-methoxymethyl- or 2-hydroxymethyl-1,3-butadiene, respectively, corresponding to the alternative mode of reaction via a cyclopropyl cation−allyl cation rearrangement.
“…Spiropentyl derivatives may undergo ionization via either one of two closely related transition states that lead to two different sets of products. The mode of reaction depends on the process; for example: ,,, …”
Section: Discussionmentioning
confidence: 99%
“…The reaction of spiropentylamine with nitrous acid in acetic acid has been reported to give 2-methylenecyclobutyl acetate and 3-methylenecyclobutyl acetate along with spiropentyl acetate in a 1:5:5 ratio . These are the products that would be expected from a spiropentyl cation that behaved as a cyclopropylcarbinyl cation.…”
The structures of spiropentyl cation and its rearrangement products have been studied via ab initio
geometry optimization at the MP2/6-31G* and B3LYP/6-311G* theoretical levels with additional
calculations at the MP4/6-311G* level. The cation was calculated to be a transition state and
underwent a cyclopropylcarbinyl to cyclobutyl cation rearrangement. This led to the products
observed in the nitrous acid deamination of spiropentylamine. A closely related transition state,
with the second cyclopropyl ring rotated 20° from the normal Cs geometry, was located. It led to a
cyclopropyl cation type ring opening to an allyl cation, which formed the products observed in the
solvolysis of spiropentyl chloride. The two transition states have essentially the same energy.
“…This description satisfactorily accounts for the unusual stability of these cations. Q (37) (381 (39) The idea that pyramidal cations are made up of molecular fragments allows us to replace CH@ by similar fragments which are isolobal with CH@, namely fragments X having the same or similar properties regarding the number, symmetry, shape, and energy of the relevant frontier orbitals[331, e.g. BH (37).…”
Section: Formal Construction Of Pyramidal Ions From Cho and 4e Systemsmentioning
Dedicated to Professor Ferdinand Bohlmann on the occasion of his 60th birthday Pyramidal cations are discussed with reference to their role as the connecting link between organic and inorganic chemistry. The electronic structure of these ions is treated with respect to their physical and chemical properties, namely charge distribution, geometry, and quenching reactions with nucleophiles. The chemistry in the gas phase of certain carbenium ions, in particular the scrambling of carbon atoms, is readily explicable by invoking transition states or intermediates of pyramidal structure. Moreover, the behavior of unimolecular processes can be understood in terms of transition states in which a hydrogen molecule is positioned as a "side-on" or an "end-on" ligand. Volume 20 -Number 12 December 1981 Pages 991 -1 066 Angew. Chem. Inr. Ed. Engl. 20. 991-1003 (1981) 0 Verlag Chemie GmbH. 6940 Weinheim, 1981 0570-0833/81/1212-0991 $02.50/0 ( 73) Nu ( 74) NU I \ I I D Scheme 7. Quenching of pyramidal cations by nucleophiles Nue. Angew. Chem. Int. Ed. Engl. 20. 991-1003 (198I) Received: July 8, 1981 [Z 390 IE] German version: Angew. Chem. 93, 1046 (1981) 11) a) H. Hogeueen. P. W. Kwant. Acc. Chem. Res. 8, 413 (1975); b) H. C. Brown (with comments by P. uon R. Schleyer): The Nonclassical Ion Problem, Plenum Press, New York 1977, Chap. 1, p. 17.121 a) R. N. Grimes: Carboranes, Academic Press, New York 1970; b) W. N .
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