An intramolecular cyclization approach to optically active cyclopentenyl bromides

Abstract

The two antipodes of l-bromo-3,3-dimethyl-4-[(tert-butyldimethylsilyl)oxy]cyclopentene, the dextrorotatory form of which ( 1) is regarded as a potential synthetic precursor to kalmanol, have been prepared in a state of high enantiomeric purity from propargyl alcohol. The key steps in the abbreviated synthetic pathway involve the bromination-dehydrobromination of aldehyde 12 to give 7, the conversion of alcohol 13 to the hydroxyl-substituted bromocyclopentene 18 by a novel tandem Claisen-Sakurai reaction sequence, and efficient enzymatic resolution of 18 via its chloroacetate ester. The absolute configurational assignments are based on 1H NMR analyses of the (R)-and (S)-MTPA esters of (-)-20.

Toward a Symphony of Reactivity: Cascades Involving Catalysis and Sigmatropic Rearrangements

“…[84] Treatment of vinyl enol ether 242 with Et 2 AlCl, followed by HCl and TBAF in the workup, resulted in facile formation at room temperature of the vinyl bromide 245 , presumably via intermediate aldehyde 243 . Thermal conditions were unsuccessful.…”

“…[82a] Borrelly and Paquette used a Claisen rearrangement/ Sakurai cyclization duet to prepare vinyl bromide 245, a cyclopentenyllithium reagent precursor that is important in their efforts toward the total synthesis of natural products (Scheme 55). [84] Treatment of vinyl enol ether 242 with Et 2 AlCl, followed by HCl and TBAF in the workup, resulted in facile formation at room temperature of the vinyl bromide 245, presumably via intermediate aldehyde 243. Thermal conditions were unsuccessful.…”

Stereochemical Control in Organic Synthesis Using Silicon-Containing Compounds

“…In some cases, bromodesilylation takes place with retention of configuration, either because the intermediate cation is so well stabilized that syn addition of bromine takes place, as with styrenes and β,β-disubstituted vinylsilanes 24 or because of syn elimination of the silyl bromide. , …”

Bis hin zu einer Symphonie der Reaktivität: Kaskaden mit Katalysen und sigmatropen Umlagerungen

“…Borrelly und Paquette verwendeten eine Claisen‐Umlagerung/Sakurai‐Cyclisierung im Duett zur Synthese des Bromids 245 , einer Vorstufe für ein Cyclopentenyllithium‐Reagens, das für ihre Totalsynthesen von Naturstoffen von Bedeutung ist (Schema ) 84. Die Behandlung des Vinylenolethers 242 mit Et 2 AlCl gefolgt von HCl und TBAF in der Aufarbeitung führte bei Raumtemperatur glatt zu dem Vinylbromid 245 , und zwar wahrscheinlich über das Aldehydintermediat 243 .…”