Synthesis and Stereochemistry of Insect Derived Spiroacetals with Branched Carbon Skeletons

Abstract

About thirty constitutionally different spiroacetals have been characterised from insects but only three have branched carbon skeletons. Two are based on the 1,7-dioxaspiro[5.5]undecane system and are certain stereoisomers of the 2,4,8-trimethyl derivative, from the aposematic shield bug, Cantao parentum (White), and a 2,2,8-trimethyl derivative from the rove beetle, Ontholestes murinus (L). The 1,6-dioxaspiro[4.5]decane system is represented by a stereoisomer of the 2,3,7-trimethyl derivative in the Cantao species. The elucidation of their structures and stereochemistry by spectroscopy, synthesis and enantioselective gas chromatography is described.

Insect chemistry and chirality

“…The location of the label was clearly shown to be vicinal to the deuterium atom by the mass spectral fragmentation pattern and, in particular, the ions at m/z 140 (M − CH 3 CHO) and 143 (plus 3 amu). This constitutes the first unequivocal demonstration that the 18 O incorporation from labeled dioxygen we had previously observed in 65 corresponds to the second oxygen atom introduced. Although predicted by our general paradigm, this observation clearly excludes other more complicated biosynthetic schemes, which could be proposed in view of the unusual double 18 O incorporation into the spiroacetals of B. cacuminata and B. oleae.…”

“…This constitutes the first unequivocal demonstration that the 18 O incorporation from labeled dioxygen we had previously observed in 65 corresponds to the second oxygen atom introduced. Although predicted by our general paradigm, this observation clearly excludes other more complicated biosynthetic schemes, which could be proposed in view of the unusual double 18 O incorporation into the spiroacetals of B. cacuminata and B. oleae. 27,28 Given our previous results with racemic 69 in B. cucumis, we expected a complex manifold of products to result from incorporation of rac-71 (Scheme 18).…”

“…The absolute stereochemistry of the components A-H (excepting B) are shown below. 17,18 Determination of the structure and stereochemistry of minor component B was more difficult. This component was initially assumed to be the (E;Z) diastereomer of 2,8-dimethyl-1,7-dioxaspiro [5.5]undecane which often accompanies the (E;E)-diastereomer (component A).…”

“…The proposal was that analysis of the incorporation of racemic and (S) and (R) Solid phase micro-extraction (SPME) and GC-MS analyses of the (E;E)-spiroacetal demonstrated that 18 O was incorporated and over time the relative intensity of the ion at m/z 184 (M + for endogenous spiroacetal) decreased and those at m/z 186 and m/z 187 increased. The m/z 186 ion corresponds to incorporation of one 18 O atom into unlabeled endogenous precursor, whereas m/z 187 arises from 18 O-oxygenation of the administered rac-71 and confirms its in vivo transformation to spiroacetal system 65. The location of the label was clearly shown to be vicinal to the deuterium atom by the mass spectral fragmentation pattern and, in particular, the ions at m/z 140 (M − CH 3 CHO) and 143 (plus 3 amu).…”

Die Totalsynthese von (−)‐Nitidasin

“…Unsere erfolgreiche Sequenz startete mit dem oxidativen Abbau von käuflichem (À)-Citronellen (12) zum in der Literatur beschriebenen Aldehyd 13. [22] Dieser wurde durch eine Corey-Fuchs-Homologisierung mit Abfangen der intermediären Alkinyllithiumspezies mit MeI zum Enin 14 umgesetzt. [23] Im Anschluss daran griffen wir auf ein von Negishi entwickeltes Cyclometallierungsprotokoll zurück, [24] um den Fünfring und das tetrasubstituierte Alkenyliodid aufzubauen.…”