Studies of cyclic acetals. XXII—limitations on the use of alkyl substituents as pseudoisotopic labels: The electron impact mass spectra of alkylated derivatives of 3,7,9‐ and 4,7,9‐trioxabicyclo[4·2·1]nonanes

Abstract

Abstract-Low resolution, electron impact mass spectra are tabulated for eleven methylated derivatives of 3,7,9-trioxabicyclo[4~2~l]nonane, 4,7,9-trioxabicyclo[4~2~llnonane and nine methylated derivatives, and 6-ethyl-3,7,9-trioxabicyclo [4*2.llnonane. In general, a substantial proportion of the fragmentation subsequent to electron impact can be rationalized according to a few, simple decomposition pathways that are inferred from analysis of mass number shifts caused by changes in substitution; however, major alterations in fragmentation are apparent in a few of these examples, which signals that, for several of the 4,7,9-trioxabicyclo[4~2~l]nonanes, the substituent acts not as an inert label but as a fragmentation-directing group.FRAGMENTATION subsequent to electron impact has been elucidated in detail for two 6,8-dioxabicyclo [3*2-l]octane derivatives, namely, 1,6-anhydro-2,3-O-isopropylidenep-D-talopyranose2 (1) and the 3,4-O-isopropylidene isomer3 (2). In an earlier paper: a partial analysis was accomplished of the fairly simple fragmentation induced by electron impact ionization of a number of methylated derivatives of 3,6,8-trioxabicyclo-[3-2.l]octane (3) and the corresponding 4-01; in the latter study, use was made of characteristic mass-number shifts caused by variations in substitution, which amounted to a pseudoisotopic labeling procedure (in contrast to such conventional isotopic labeling techniques as de~teration),~ as the major fragmentation processes appeared to depend only quantitatively on the extent and location of alkylation, whereas introduction of an exocyclic, oxygenated group at C-4 caused some new fragmentation modes to appear.4 These observations illustrate the principle formulated by Biemanna that, within a series of structurally related molecules, variations in substitution will result in characteristic shifts of mass number of common fragments unless the substituent acts to alter the relative stability of the possible fragments. Additional modes of fragmentation resulting from the presence of two oxygenated substituents in the 7-(S)-acetoxy-2-(S)-methoxy derivative of 3 complicate considerably its mass spectrum.' t For Part XXI, see Ref.1.

Studies of cyclic acetals. XXIII—low resolution, electron impact mass spectra of some 6,8‐dioxa‐3‐thiabicyclo[3.2.1]octanes and related 2‐acetoxy, 3‐oxo and 3,3‐dioxo derivatives

“…Whereas the mass spectrometric literature abounds with reports about oxygenated heterocycles, there is a paucity7 of data for mixed heterocycles containing both oxygen and sulfur atoms. 6,8-Dioxa-3thiabicyclo[3.2.1]octane (1) has been known for a decade; its preparation (Scheme 1, method A) by the action of sodium sulfide on 2,4-di-(p-tolylsulfonyloxy-* or ~h l o r o -~ methyl)-1,3-dioxolane was extended" ret For Part XXII, see Ref. 1. cently to the preparation of 2 and 5-7.…”

Hétérobicycles oxygénés. Synthèse d'alkyl-3,6,8-trioxabicyclo[3.2.1]octanes et d'alkyl-3,7,9 et -4,7,9-trioxabicyclo[4.2.1]nonanes

“…La synthese de dioxolannes bifonctionnels (12) permettait d'envisager l'acces a deux series isomeres: les 3,7,9-et les 4,7,9-trioxabicyclo[4.2.I]nonanes. Tous les cornposCs correspondant dCcrits dans le present rnCrnoire ont Ct C par ailleurs CtudiCs en spectrographie de rnasse, afin dlCvaluer les possibilitts d'utiliser des groupements mCthyle comrne marqueurs de la fragmentation (13).…”