The Proton Magnetic Resonance Spectra of Some α-Acetoxy Ketones

2,3-Benzo-1-azabicyclo[2•2•1]hept-2-ene derivatives have been prepared by the introduction of a two-carbon bridge between positions-1 and -3 of the indole ring in 2,3-dimethylindole and tetrahydrocarbazole. In the former case both C-7 epimers were isolated and identified, and their nuclear magnetic resonance spectra were analyzed in detail. In the tetrahydrocarbazole series only one product was obtained and some ambiguity remains concerning the stereochemistry of this material. The physical properties of these compounds are of interest because the lone pair electrons on nitrogen are not able to overlap with the aromatic π system; the chemical properties are characterized by a facile cleavage of the tertiary amine under acylating conditions.

Section: Oxidationmentioning

confidence: 99%

Derivatives of 2,3-benzo-1-azabicyclo[2•2•1]hept-2-ene

McLean¹,

Fallas²,

Trotz³

et al. 1969

“…I t can be noted that recent reports of coupling constants of comparable magnitude have appeared for other fused ring systems (12,14,33,34) having protons in a similar orientation and also for vicinal cases in which there are small dihedral angles of ca. 20" (35,36).…”

Section: Stereochemistry At (2-21 and C-ddmentioning

confidence: 99%

The Stereochemistry of Maleopimaric Acid and the Long Range Shielding Effect of the Olefinic Bond

Ayer¹,

McDonald²,

Stothers³

1963

Nuclear magnetic resonance studies of methyl maleopimarate and closely related derivatives clearly establish the stereochemistry of methyl maleopimarate and, consequently, levopimaric acid. An extension of this study to other related compounds, 22 in all, provides evidence, on the basis of an intercomparison of the chemical shifts for the angular methyl protons, to support the original suggestion by Jackman (Applications of NMR in organic chemistry. Pergamon, S e w York. 1959. Chap. 7) that the long range shielding effect of the olefinic linkage is analogous to that of the carbonyl double bond. Coupling constants and chemical shifts for some of the protons of the bicyclo[2.2.2]octene system present in these compounds are also discussed.

“…4). When the dioxolenium ring is fused to an anchored cyclohexane system one oxygen is in an equatorial configuration and the other axial.…”

Section: Introductionmentioning

confidence: 99%

Remarkable stereoselectivity in the hydrolysis of dioxolenium ions and orthoesters fused to anchored six-membered rings

King¹,

Allbutt²

1970

108

Hydrolysis of dioxolenium (acyloxonium) ions fused to anchored six-membered rings gives almost exclusively that hydroxyester in which the ester function is axial (and the hydroxyl group equatorial). With the exception of the orthoformate, a group of related orthoesters reacted similarly. The potential utility of these observations in stereoselective synthesis is suggested by the following examples. (a) With trans-decalin-cis-2,3-diol (21) formation of the mono-benzoate via the orthoester leads to the axial ester (23d) in good yield; this procedure is complementary to reaction with benzoyl chloride and pyridine, which gives the equatorial ester (24d) as the only isolated product. (b) The action of silver acetate and iodine in wet acetic acid (the Woodward-Prkvost reaction) on trans-A'-octalin gives the axial acetateequatorial alcohol (236) again as the only significant product. The generality of this stereoselectivity is further supported by a number of individual examples drawn from the chemistry of carbohydrates. A rationalization is offered which qualitatively accounts for the observed stereoselectivity and its absence in the hydrolysis of the orthoformate, and which is based on the differences in steric strain among the possible transition states that fulfil the stereoelectronic requirements of dialkoxycarbonium ion formation.