Download e-book for kindle: Asymmetric Organocatalysis in Natural Product Syntheses by Mario Waser
By Mario Waser
ISBN-10: 3709111625
ISBN-13: 9783709111628
This ebook offers the reader with an illustrative assessment referring to profitable and everyday functions of organocatalysis within the box of ordinary product synthesis. the focus should be on organocatalytic key-steps for every (multi-step) synthesis defined, while different usually quite cutting edge alterations could be passed over, as this could be past the scope of this volume.
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Additional info for Asymmetric Organocatalysis in Natural Product Syntheses
Example text
123, (R)-12 (10mol%) C10H21 CHO 2. allyl bromide In ONHPh O C10H21 OH 67% 137 (99% ee, dr = 4:1) 136 (+)-Disparlure (135) Scheme 32 Total synthesis of (+)-disparlure (135) N H Ph OTMS Ph (S)-138 1. BzOOBz, HQ (S)-138 (5mol%) C10H21 CHO 136 2. allyl bromide In 44% OAc OBz O C8H17 C10H21 O OH 139 (95% ee, dr = 86:14) 28 Scheme 33 Enamine-catalyzed a-oxygenation in the synthesis of (À)-(5R,6S)-6-acetoxy-5hexadecanolide (28) moth, Porthetria dispar (118), whereas the (À)-enantiomer has been shown to antagonize this effect (119).
The imidazoline salt 253 was reported recently by Willis et al. to be the catalyst of choice in an iminium-catalyzed transfer hydrogenation (using ester 247 as a hydride donor) of an (E)/(Z)-mixture of the a,b-unsaturated aldehyde 254 to furnish the chiral aldehyde 255 in good yield and enantioselectivity (221). 2 eq) 254 (E:Z = 3:1) N N S 255 N Dysideaproline E (256) 85% (90% ee) Scheme 58 Enantioselective transfer hydrogenation in the synthesis of (À)-dysideaproline E (256) 255 in hand, the total synthesis of dysideaproline E (256) could be accomplished in a short period of time and in a straightforward manner (Scheme 58).
Dysideaproline E (256) belongs to a family of chlorinated natural products isolated from extracts of a Dysidea sp. from the Philippines (222). 2 Carbon Nucleophiles in Michael-Type Reactions Carbon-carbon bond forming reactions between carbanionic nucleophiles like enolates or deprotonated nitroalkanes and electron deficient alkenes and alkynes belong to the oldest and most versatile transformations known today (223–229). Moreover, stereoselective variants have proven to possess an enormous potential in the syntheses of complex molecules as already exemplified in Sect.
Asymmetric Organocatalysis in Natural Product Syntheses by Mario Waser
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