Enantioselective synthesis bromination

Section B shows some Hofmann rearrangements. Entry 9, using basic conditions with bromine, provided an inexpensive route to an intermediate for a commercial synthesis of an herbicide. Entry 10, which uses the Pb(OAc)4 conditions (see p. 949), was utilized in an enantiospecific synthesis of the naturally occurring analagesic (-)-epibatidine. Entry 11 uses phenyliodonium diacetate as the reagent. The product is the result of cyclization of the intermediate isocyanate and was used in an enantioselective synthesis of the antianxiety drug (tf)-fluoxetine. 

A novel strategy for the enantioselective synthesis of polyhydroxypiperidines 141, which can be viewed as amino 2,6-dideoxyazasugars, was developed based on 5-bromo-4-bromomethyloxazole 139 and JV-protected a-amino esters alkylation and bromine-lithium... 

Bromoetherification has been used for the enantioselective synthesis of polysubstituted furans170,171. calonectrin and deoxynivalenol172. The final products, again, do not contain bromine. 

The direct derivatization of the chiral brominated precursor shown below (x = 0.2) gave the corresponding silyl phosphazene copolymers (188) where the phosphine ligands sit inside wide and sterically demanding chiral pockets, and therefore, with potential interest to support catalysts for enantioselective synthesis. ... 

On the other hand, however, trimethylsilyl-protected catalyst 18 was suitable for the asymmetric bromination of aldehydes, and the resulting a-bromoaldehydes can be diastereoselectively transformed into the corresponding bromohydrin in one-pot (Scheme 7.31) (54). An additional utility of catalyst 18 was highlighted by application to the development of the direct aminoxylation of aldehydes with an oxoammonium salt generated from 2,2,6,6-tetramethylpiperidine 1-oxyl (TEMPO) by in situ oxidation with benzoyl peroxide, allowing for the highly enantioselective synthesis of stable a-aminoxy aldehydes, which could subsequently be reduced to the corresponding alcohol (55). 

The synthesis of both enantiomers of vasicinone has been carried out using almost entirely polymer-supported reagents. The route was based on functionalisation of deoxyvasicinone by a highly selective bromination then via enantioselective reduction of the derived ketone <06SL2609>. 

White and coworkers used trans Addition of bromine and (-)-l-bomeol to 3,4-dihydro-2//-pyran to afford the stereoisomeric bomyl bromotetrahydropyranyl ethers (3) and (4 Scheme 44) which are employed in an enantioselective total synthesis of (-)-monic acid C (Scheme 5).10 A simple synthesis of 4-methylthio-l,2-dithiolane, the photosynthesis inhibitor of the green alga Chara globularis (Scheme 45),83 exploits the observation that allylic sulfides undergo rearrangement on addition of bromine.84 Block and Naganathan employed the trans addition of bromine to 4-thioacetoxycyclopentene as a key... 

Somewhat between diastereoselective and enantioselective approaches is the Cram s synthesis involving the oxazolines with chiral alkoxide leaving groups [26]. In this manner, bromine in oxazoline 596 was substituted with sodium alkoxides, derived from readily available natural alcohols such as menthol (597), fenchyl alcohol (598), bomeol (599), quinine (600), and quinidine (601) to give the respective chiral oxazolines 602-606, Scheme 10. The Meyers reaction of oxazolines 602-606 and 1-naphthylmagnesium bromide (608) was effected at low temperatures (-42 °C) affording the expected biaryl 609 with respective chiral induction. 

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