Regio- and Stereoselectivity of Water Elimination as a Function of Ring Size

Abstract

The elimination of water from tertiary alcohols was studied for carbocycles of ring size 5-16. The resulting olefins 3-5 were discriminated by NMR spectroscopy. The relative amount of their formation reflects the steric idiosyncrasies of the respective ring systems. The behavior of the medium-sized rings yielded experimental proof to the I-strain concept.

Syntheses of the fragrance hydroxyambran using hydrogenation methods

“…These successful hydrogenations required the presence of the base sodium methoxide (entries 2, 3), as reported in the literature. [20] However, an introduction of bulky t-butyl groups into the phosphine moiety (D), the substitution of chloride for tetrafluoroborate (E) and the presence of five membered PN ligands (F, G, H) in Rucomplexes of this type resulted in dramatic losses of catalytic activity (entries [4][5][6][7][8]. It is important to note that use of the catalyst B resulted in worsening conversion degrees at hydrogenation temperatures above 100°C, possibly due to a thermal decomposition of the Ru-complex under such conditions.…”

“…Up to now, two synthesis strategies have been reported for this compound, starting from cyclododecene or cyclododecanone . Both routes include: (a) combination of C12 moieties with appropriate C3 building blocks; and (b) hydrogenation of double bounds in the intermediates formed to produce the final product.…”

“…Unfortunately, the reactions between cyclododecene and propanoic acid or propylene oxide as initial reaction steps of the first route produce unsatisfactory yields of the resulting C15 key precursors of hydroxyambran. The second, more effective, route is commenced by the reaction between cyclododecanone and ethyl 2‐brompropanoate (Reformatskij reaction and subsequent acid catalysed dehydration of the tertiary alcohol formed) . In this way, a mixture of unsaturated ester isomers as the appropriate starting material for the fragrance is obtained with high yield.…”

“…Up to now, two synthesis strategies have been reported for this compound, starting from cyclododecene [1][2][3] or cyclododecanone. [4][5][6] Both routes include: (a) combination of C12 moieties with appropriate C3 building blocks; and (b) hydrogenation of double bounds in the intermediates formed to produce the final product. Unfortunately, the reactions between cyclododecene and propanoic acid [1] or propylene oxide [2,3] as initial reaction steps of the first route produce unsatisfactory yields of the resulting C15 key precursors of hydroxyambran.…”

“…The second, more effective, route is commenced by the reaction between cyclododecanone and ethyl 2-brompropanoate (Reformatskij reaction and subsequent acid catalysed dehydration of the tertiary alcohol formed). [4][5][6] In this way, a mixture of unsaturated ester isomers as the appropriate starting material for the fragrance is obtained with high yield. Afterwards, the ester function of these isomers is converted into a primary hydroxyl group with lithium aluminum hydride.…”