BROMIDES, EFFICIENT SYNTHESIS

EFFICIENT SYNTHESIS OF BROMIDES FROM CARBOXYLIC ACIDS CONTAINING A SENSITIVE FUNCTIONAL GROUP DEC-9-ENYL BROMIDE FROM 10-UNDECENOIC ACID (1-Decene, 10-bromo-)... 

The utility of the copper/Taniaphos-catalyzed allylic alkylation was further illustrated in two subsequent reports. The application of aliphatic allylic bromides containing protected alcohols and amines leads to the efficient synthesis of bifunctional building blocks (Scheme 15) . ... 

Sonawane et al. (Sonawane et al., 1994) described a practical and efficient synthesis of fenoprofen using commercially available m-phenoxybenzaldehyde as the starting material. The key step in the synthesis is the transformation of the a-hydroxyacetal (i) into its chlorosulfonyl ester in situ and its concomitant rearrangement to the methyl ester (ii) in high yields. The required a-hydroxyacetal (i) can be readily prepared from m-methoxybenzaldehyde by the routine sequence of reactions Grignard reaction with ethyl bromide or chloride, oxidation and finally a-chlorination with CuCI2-LiCI/DMF. 

A more efficient synthesis has been described by Nicolaides et al.[3l and TenBrinld4 (Scheme 2). The key step of the synthesis is an intramolecular Williamson s reaction between a bromide and an alkoxide to provide l,4-oxazin-5-ones 3. The cyclic product is subsequently hydrolyzed to the desired methyleneoxy dipeptide. This method provides better yields and allows for the preparation of dipeptide surrogates containing bulky side chains. 

Methyl 2,3-di-0-benzyl-oc-D-glucopyranoside gives 58% of 2,3,6- and 21% of 2,3,4-tri-0-benzyl ether on reaction with 1.4 equiv. of sodium hydride and benzyl bromide [71]. In a remarkably selective reaction, 62% of methyl 2,4,6-tri-0-benzyl-a-D-glucopyranoside result from the unprotected methyl a-D-glucopyranoside [74]. Benzyl chloride has been used for this transformation, as well as for the efficient synthesis of methyl 2,4-di-0-benzyl-a-D-xylopyranoside [75] 1 As expected, OH-2 in methyl 4,6-0-benzylidene-a-D-glucopyranoside is more reactive [71] than OH-3. 

A new, efficient synthesis of ubiquinone (249) has been described.115 In the key step, 6-bromo-2,3-dimethoxy-5-methylhydroquinone diacetate (257) is treated with l,l-dimethyl-7r-allyl-, 7r-geranyl-, 7r-solanesyl-, ir-decaprenyl-, or 7r-phytyl-nickel bromide (258)—(262) in HMPA at 60 °C, to afford a 70% yield of 2,3-dimethoxy-5-methyl-6-prenylhydroquinone diacetate (263). Ubiquinones-1, -2, -9, and -10 (250)—(253) and 6, 10, 14 -hexahydroubiquinone-4 (254) have been prepared by this method. The preparation of tritium-labelled 5-demethoxy-ubiquinone-9 (255) has been described.116... 

Efficient Synthesis of Bromides from Carboxylic Acids Containing a Sensitive Functional Group. 

DiMauro and co-workers [67] have developed a rapid and efficient synthesis of 3-amino-imidazopyridines 16 using a microwave-assisted one-pot cyclization. The intermediate 15 was further reacted with various aryl bromides in the presence of a catalytic amount of Pd(dppf)Cl2 to yield the target compounds 16. The reaction scope is quite broad with respect to the aldehyde and aryl bromide components which might be electron-rich, electron-poor, aromatic, aliphatic, or sterically encumbered (Scheme 15). 

Yang D, Kwon M, Jang Y et al (2010) A convenient and efficient synthesis of C-carbamoyl-1,2,3-triazoles from alkyl bromide by a one-pot sequential addition conversion of ester to amide using Zr(Ot-Bu)4. Tetrahedron Lett 51 3691-3695... 

There are only a few reports in this area. Reaction of a pyrazolyl disulfide 377 with bromotrifluoromethane and ethyl bromide in the presence of sodium dithionite at room temperature afforded pyrazolyl sulfides 378. Oxidation of these with hydrogen peroxide in trifluoroacetic acid afforded sulfenylpyrazoles 379 in excellent yields (Scheme 41) <2006JFC(127)948>. Pyrazole-4-carbaldehyde 380 has been utilized in the efficient synthesis of... 

Dibromo-2,2 -bisbenzimidazoles 692 react with aryl zincates under Negishi coupling conditions to give 4,4 -bisaryl-2,2 -bisbenzimidazoles 693 (Scheme 168). Lower yields were obtained with heteroaryl zincates (2- or 3-pyridyl) <2006OL4989>. Cross-coupling of bromides 694 with phosphonites provided an efficient synthesis of phosphonates 695 <1998TL2797>. 

Kartha, K P R, Field, R A, Glycosylation chemistry promoted by iodine monobromide efficient synthesis of glycosyl bromides from thioglycosides, and 0-glycosides from disarmed thioglycosides and glycosyl bromides, Tetrahedron Lett., 38, 8233-8236, 1997. 

An early example having potential commercial importance comes from tlie Trost laboratory s synthesis of vitamin D analogs (Scheme 6-23) [51], Their combination of vinyl bromide 129 and alkyne 130 to form triene 131 led to a concise and efficient synthesis of (-i-)-alphacalcidiol (134). In this reaction, vinyl bromide 129 participates in a bimolecular Heck reaction with alkyne 130 and the resulting alkenylpalladium intermediate 133 undergoes subsequent intramolecular Heck reaction with the pendant terminal alkene to provide 131. Under the reaction conditions, some of the desired product undergoes a [1,7]-hydrogen shift to yield 132. After thermal recycling of the minor component, a remarkable 76% yield of 131 was obtained. 

A simple and efficient synthesis of juvabione (58) (c/. Vol. 1, p. 60 Vol. 5, p. 49 Vol. 4, p. 88), a sesquiterpenoid possessing juvenile hormone activity, has been achieved using a combination of hydroboration and carbonylation reactions cf. Scheme 6). A new efficient synthesis of ( )-a-curcumene (59) cf. Vol. 5, p. 51) involves reduction in situ (Li-NHs) of the alkoxide produced from p-tolylmagnesium bromide and 6-methylhept-5-en-2-one. ... 

Acid chlorides couple with arylstannanes to form ketones in HMPA solution in the presence of chlo-robis(triphenylphosphinebenzyl)palladium. The same methodology has been used as part of a very efficient synthesis of manoalide and its seco derivative. The coupling of aroyl chlorides with benzylzinc bromides also produces arylbenzyl ketones under palladium catalysis.The benzylzinc bromides are formed in situ. ... 

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