Chemoselective coupling

Scheme 5.8 Armed/disarmed concept for chemoselective coupling of two w-pentenyl glycosides (NPGs). A 2-0-alkylated (armed) NPG 29 is much more readily activated than is a 2-0-acylated (disarmed) NPG 30.62...

The reaction of chromenes with mono- and bis- imides of 1,4-benzoquinones (6, X = O or NCOPh) is promoted by Lewis acids and affords pterocarpans and azapterocarpans, respectively (95TL2713). A total synthesis of the pterocarpan, neorautenane, involves a chemoselective coupling of a benzodipyran with o-chloro-mercuriophenol (95JCS(P1)949). 

Ley and coworkers reported the one-pot synthesis of tetrasaccharide 176 by combining selective activation with reactivity-based armed-disarmed glycosylation [113]. As shown in Scheme 6.35, the first chemoselective coupling was achieved via selective activation of the fluoride donor 173 over the selenoglycoside acceptor 174. The resulting disaccharide intermediate was more armed than the bifunctional... 

Mechanistically, the one-pot transformation can be rationalized by a sequence of chemoselective coupling of ort/to-halogenated (hetero)aromatic acid chlorides 81 and electron rich terminal alkynes 4, followed by nucleophilic addition of the sulfide ion to the a,p-unsaturated system 86 to furnish the anionic Michael adduct 87, and finally an intramolecular nucleophilic aromatic substitution in the sense of an addition-elimination process concludes the sequence (Scheme 46). 

Chemoselective coupling of lactose and an oxylamino-functionalized amino acid residue... 

This method of imidazolylzinc chloride synthesis has also found application in the synthesis of a sulfonyl chloride to be used in the preparation of some potential factor Xa inhibitors [17]. Thus, following imidazole metalation and quenching with ZnCl2, a chemoselective coupling reaction occurred to provide 16. Treatment with sulfur dioxide provided the sulfinic acid, which upon treatment with thionyl chloride, provided the requisite sulfonyl chloride 17. 

Coupling reactions. Sequential and chemoselective coupling reactions have been developed for 3-chloro-4-arylthio-l,2-cyclobutenones. Thus a Stille coupling replaces the chlorine atom with a Suzuki coupling to follow. Two different Pd complexes are used. ... 

Silastannylation of alkynes. The partitional difunctionalization is achieved using a catalytic system of Pd(OAc)j-RNC at room temperature (75-99% yield). The many chemoselective coupling procedures available to vinyltin and silicon compounds make these product extremely valuable for synthetic quests. 

A versatile and regio- and stereoselective synthetic method of terpenoids containing 1,5-diene units has been developed by Negishi. Chemoselective coupling of the alkylzinc bromide 49 with the alkenyl iodide in 50 provided 51. The alkyl iodide in 51 was converted to alkylzinc bromide, which was coupled again with the alkenyl iodide 50 to provide 52. Coenzyme Qio (53) was synthesized in 26 % overall yield by repeating a similar sequence of the coupling reactions [61]. 

The biphenyl-based phosphine 34 was prepared from 2-bromoiodobenzene (29). Chemoselective coupling of the iodide in 2-bromoiodobenzene (29) with diphenylphosphine (1) gave 2-bromophenyldiphenylphosphine (30), and its Suzuki-Miyaura coupling with 31 afforded the biphenylylphosphine 32. Reaction of 29 with the primary phosphine 8 afforded the di(2-bromophenyOphenylphosphine (33), and bis-biphenylylphosphine derivative 34 was obtained by Suzuki-Miyaura coupling of 33 with 31, although the yield was not high [2]. 

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