Alpine synthesis

Fig. 7. Preparation of Alpine-borane (93) and use in the synthesis of homochiral butyrolactones and arylhydroxytetronic acids. Rg and denote small and...

The synthesis of chiral liquid-crystalline allenes was reported by Tschierske and co-workers (Scheme 4.10) [14]. An asymmetric reduction of 41 with Alpine borane was a key step to an enantioenriched allene 44. After removal of the silyl group, the allenic alcohol was etherified by the Mitsunobu method to give 45, the first liquid-crystalline allene derivatives. 

Synthesis Features of Alpine Waters and Management Concerns... 

The goal of this chapter is to summarize the composition and community patterns of algae (with special consideration to benthic diatoms), zoobenthos, and fish that occur in Alpine freshwaters. The data presented are a synthesis of published research and represent the current state of knowledge on the different groups. The chapter closes with a general perspective on the biodiversity of alpine freshwaters. 

Highly enantioenriched 4-alken-l-yn-3-ol moieties present in many bioactive acetylenic metabolites from sponges have been efficiently obtained by reduction of the parent 1-trimethylsilyI-4-alken-l-yn-3-one 18 with Alpine-borane or with BH3-SMe2 in the presence of chiral oxazaborolidines, followed by desilylation of the resulting alcohol. This strategy has been applied to the first stereoselective synthesis of petrofuran 19 <99SL429>. 

The above described total synthesis features the first enantiodivergent approach to (+)- and (—)-scopadulcic acid A. The central transformations are the stereoselective carbonyl group reduction with (S)-Alpine Borane , the use of enolization stereoselection to dictate which enantiomer is produced, and the palladium-catalyzed bis-Heck cyclization which occurs with complete stereo- and regiocontrol to establish the scopadulan scaffold. 

L. A., Hall, M.J., Alpin, R.T. and Anserson, H.L. (2000) Insulated molecular wires Synthesis of conjugated polyrotaxanes by Suzuki coupling in water. Angewandte Chemie (International Ed. in English), 39, 3456-60. 

Ernst W. G. and Ottonello G. (1984) Synthesis of trace element geochemistry for five western Alpine Iherzolites. Ofioliti 9, 425-442. 

The first total synthesis of the neuritogenic spongean polyacetylene lembehyne A was accomplished by M. Kobayashi and co-workers. The single stereocenter of the molecule was introduced via the Midland reduction of a propargylic ketone using an Alpine-Borane , which was prepared from (+)-a-pinene and 9-BBN. 

Alpine borane (the Midland reagent, 3) has found broad use in the synthesis of complex natural products. As early as 1980, only one year after Midland s seminal publication, Johnson and co-workers used 3 for the reduction of ketone 18 to afford alcohol 19 in 75% yield and 97% ee.12 This material was used to complete the synthesis of 20, a cyclization precursor in Johnson s total synthesis of hydrocortisone acetate. 

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