Solvolysis of trans-2,2-dimethyl-3-(2'-methylpropenyl)cyclobutyl tosylate. Model reactions relevant to squalene biosynthesis

Rm, Coates; Wh, Robinson

doi:10.1021/ja00771a079

Cited by 18 publications

(18 citation statements)

References 2 publications

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“…In a previous experiment using the same procedure, a sample of cold 12 (59 mg, 0.14 mmol) was converted to 2 (20 mg, 22%): 'H NMR (300 MFIz, CDC13) 5.05 (br s, 4 H, vinyls), 4.87 (d, J = 8 Hz, vinyl adjacent to C3'), 4.0-2.6 (br, ammonium counterions, carbinyls), 1.96 (m, 16 H, vinyl methylenes), 1.64 (m, 9 H, vinyl methyls), 1.55 (s, 12 H, vinyl methyls), 1.4-0.8 ppm (unresolved resonances for the cyclopropyl methyl and Cl' and C3' cyclopropyls); 31P NMR (121 MHz, CDC13) -9.4 (br s, 1 P, P2), -11.3 (br s, 1 P, PI); negative ion FABMS, m/z (rel intensity) 585 (M -NjH,0, 25), 189 (11), 181 (12), 177 (14), 159 (30), 97 (16).…”

Section: Methodsmentioning

confidence: 99%

Squalene synthetase, inhibition by ammonium analogs of carbocationic intermediates in the conversion of presqualene diphosphate to squalene

et al. 1989

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Section: Methodsmentioning

confidence: 99%

Squalene synthetase, inhibition by ammonium analogs of carbocationic intermediates in the conversion of presqualene diphosphate to squalene

et al. 1989

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“…The incipient steric interaction between eclipsing groups in the solvolytic transition state from the cis isomer is responsible for its slower rate (76). Hydrolysis ofthe model cyclobutyl tosylates in the presence of sodium borohydride furnishes the squalene-like diene (295a, 34%) and its double isomer 303 (12%) as weil as the same two dienols (39~~) mentioned previously (380). The reaction of 298-0Ts with pyridine in benzerre at 70°, conditions conducive to formation of elimination products, provides symmetrical phytoene-like triene 296a (56~~) and its positional isomer 304 (28%).…”

Section: References Pp 205~230mentioning

confidence: 77%

“…7 -2) In cantrast to the very inefficient rearrangement of 16-0Py+ I-to squalene-like products, hydrolysis of trans-cyclobutyl tosylate (298-0Ts), a potential progenetor of ion 293 (R = CH3), affords dienals 300-0H and 301-0H in high yield (82-95%) (67,(380)(381)(382). Since the same product mixture is obtained from hydrolysis of the cyclopropylcarbinyl p-nitrobenzoate 299-0PNB, the two reactions presumably pass through a common cationic intermediate which is very likely the tertiary cyclopropylcarbinyl carbonium ion 297 (R = CH3).…”

Section: References Pp 205~230mentioning

confidence: 99%

“…It is significant that trans-cyclobutyl tosylate 298-0Ts is much more reactive in solvolysis than its cis isomer (k ''""' I kc~, = 250) (380,381) as is commonly the case with 3-substituted cyclobutyl sulfonates (76). The * A certain amount (17%) of unrearranged cyclopropylcarbinol (302-0H) is assumed to have been formed by a direct SN2 displacement (k, pathway).…”

Section: References Pp 205~230mentioning

confidence: 99%

“…The absence of pertinent experimental information has not inhibited speculation upon means by which enzymatic control might be achieved. Since allylic stabilization provides a driving force for rupture of the C1-C3 bond, it has been suggested that immobilization of the adjacent double bond within the active site such that the porbitals are approximately orthogonal to the C1 -C3 bond of presqualene pyrophosphate might help to prevent premature ring scission (380). Another explanation invokes the inftuence of the pyrophosphate counter-ion Fortschntte d. Chem.…”

Section: References Pp 205~230mentioning

confidence: 99%

See 2 more Smart Citations

Biogenetic-Type Rearrangements of Terpenes

Coates

1976

Fortschritte Der Chemie Organischer Naturstoffe / Progress in the Chemistry of Organic Natural Products

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Ketene Cycloadditions

1994

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The reaction of ketene with itself was described almost simultaneously in 1908 by Chick and Wilsmore in England, and by Staudinger and Klever in Germany; priority for the discovery was attributed to Wilsmore by the German group. Ketene cycloaddition was an early example of a peculiar process, one that formed carbon–carbon bonds with ease, often without the need for solvent, catalyst, or high heat. Subsequent work by others was done in the shadow of Staudinger's exhaustive and rigorous study of all phases of ketene reactivity. Three factors led to a resurgence of interest in this reaction beginning in the 1960s. Haloketenes, which had previously eluded study, were found to have high reactivity, and the halogens could easily be removed after the reaction. The increasing sophistication of powerful analytical methods, particularly nuclear magnetic resonance spectroscopy, led to discovery of the interesting stereochemical aspects of this reaction. Finally, the new theory of orbital symmetry conservation provided a conceptual framework to rationalize these puzzling “no mechanism” reactions. This chapter is a review of cycloaddition reactions of ketenes. Here, a cycloaddition is defined as a reaction of a ketene with an unsaturated organic compound to give a cyclic product by a mechanism that, in principle, involves the almost simultaneous formation of two bonds between two reactants. While there is no concern here as to whether bond formation is concerted or stepwise, no other chemical process can take place between the formation of the first and second bond. Definition here involves both structural and mechanistic factors, and it is difficult to avoid a certain amount of arbitrariness. Products, such as dehydroacetic acid, which seem to us to arise by concatenation of ketene molecules followed by cyclization are excluded. These reactions, are more properly considered to arise from a series of ionic reactions, and the prediction of the eventual product does not take advantage of the special mechanistic features commonly associated with true cycloadditions. Additions to imines to give β‐lactams are numerous and will be covered in a separate review. The literature has been searched to the end of 1988. Many reviews devoted partially or exclusively to ketene cycloadditions have been published. Specific topics that have been reviewed include haloketenes, fluoroketenes, cyanoketenes, intramolecular cycloadditions, conjugated ketenes, and β‐lactam antibiotics. Ancillary topics pertinent to ketene cycloadditions that have been reviewed include cycloreversion reactions, ketene equivalents, which provide ketene functionality with olefin‐like reactivity especially in [4 + 2] reactions, application of frontier molecular orbital theory to cycloadditions, and a critical discussion of cycloadditions with polar intermediates. Applications of cyclobutanones in synthesis have also been reviewed.

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Solvolysis of trans-2,2-dimethyl-3-(2'-methylpropenyl)cyclobutyl tosylate. Model reactions relevant to squalene biosynthesis

Cited by 18 publications

References 2 publications

Squalene synthetase, inhibition by ammonium analogs of carbocationic intermediates in the conversion of presqualene diphosphate to squalene

Squalene synthetase, inhibition by ammonium analogs of carbocationic intermediates in the conversion of presqualene diphosphate to squalene

Biogenetic-Type Rearrangements of Terpenes

Ketene Cycloadditions

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