Remote functionalization of hydrocarbons with reversibility enhanced stereocontrol

Abstract

Remote functionalization of hydrocarbons could be achieved through successive zirconocene-mediated allylic C–H bond activations followed by a selective C–C bond cleavage.

Pd‐Catalyzed Selective Remote Ring Opening of Polysubstituted Cyclopropanols

“…This pathway is therefore a non‐productive pathway and either the Pd species disengage from the intermediate alkenyl–H[Pd]X or through a reversible Pd‐walk and H−PdX elimination with different hydrogens, the Pd changes stereoface to reach IIb . In this case, a syn ‐periplanar relationship between the Pd and the cyclopropanol leads to the ring‐fragmentation, producing the desired products 2 with an exclusive E ‐double bond …”

“…[9] This strategy was successfully used for differentP d-catalyzed metal walk [10] and to trigger selective ring-opening of cyclopropanes. [11] This concept of remote functionalization is nowadays getting morea nd more attractive as it allows not only the catalytic functionalization of moleculesa tu nreactive positions, [12] but also the possibility to merget wo independentr eactions at unrelated sites. [13] We envisaged that the strategy of remote functionalization would be suitable for the preparation of aldehydes possessing aq uaternary stereocenter in a-position to the carbonyl group with ap olysubstituted doubleb ond by combining the sequence of Pd-catalyzed Heck addition (formation of I)-Pd walk (formation of II)-selective ring-fragmentation (formationo fIII)w ith at erminal step revealing the aldehyde through aH À[Pd]ÀXe limination and concomitantly regeneration of the catalyst( Scheme 1c).…”

Synthesis and Stereochemical Assignment of Crypto‐Optically Active 2H6‐Neopentane

“…Our strategy for the preparation of both enantiomers of 2 H 6 -1 (Scheme 1) was to promote the transformation of the easily accessible w-ene cyclopropanes [10] as well as alkylidenecyclopropanes [11] into acyclic molecular fragments by merging two modes of chemical activation. [12] Indeed, through the use of au nique organometallic species,s uccessive allylic C À Hb ond activations followed by as elective C À Cb ond cleavage and selective functionalization with two different electrophiles, [10] complex molecular architectures possessing aq uaternary carbon stereogenic center [13] were readily constructed from common starting materials.…”

Synthese und stereochemische Bestimmung von krypto‐optisch‐aktivem 2H6‐Neopentan

“…Unsere Herangehensweise für die Synthese beider Enantiomere von 2 H 6 -1 (Schema 1) war die Umformung des einfach zugänglichen w-En-Cyclopropans [10] sowie des Alkylidencyclopropans [11] in acyclische Fragmente durch die Kombination zweier Aktivierungsstrategien. [10] Wirv ermuteten daher, dass eine Kontrolle über die Art der Aktivierung erfolgreich dafür genutzt werden kann, (R)-1 und (S)-1 ausgehend von einfach zugänglichem, enantiomerenreinem Alkylidencyclopropan herzustellen ( 2 H 3 -2;S chema 1, e.r. [14,15] Dies erfolgte durch sukzessive Aktivierung einer allylischen C-H-Bindung mit anschließender selektiver C-C-Bindungsspaltung,gefolgt von einer selektiven Funktionalisierung mit zwei verschiedenen Elektrophilen.…”