2-oxo bromide

Access to p-mannosides can be achieved by epimerising the C-2 hydroxyl group of a P-glucoside, however this can be synthetically time consuming [35]. A more efficient alternative to the deprotection, oxidation, reduction methodology was developed by Lichtenthaler and co-workers and focused on the use of 2-oxo bromide 17 as the glycosyl donor [23]. Access to 2-oxo bromide 17 can be achieved from acetobromoglucose 18 in a simple 4-step synthetic sequence with an overall yield of 54% (Scheme 8.5). 

Furstner and Konetzki have successfully adopted this approach for the synthesis of the fungal metabolite 1 [15]. Treatment of 2-oxo bromide donor 17 with alcohol 27 in the presence of aluminosilicate solely afforded (3-glycoside 28, which was reduced without further purification with sodium borohydride. Mannoside 29 was obtained in a 78% yield over two steps with excellent stereoselectivity (Scheme 8.7). 

Benzothiazolin-3-ylacetic acid, 4-chloro-2-oxo-as herbicide, 6, 328 as plant growth regulator, 1, 191 Benzothiazolium bromide, 2-methyl-3-propargyl-nucleating agent... 

Reaction of 2-oxo-2,3-dihydropyrido[l,2,3- /e]-l,4-benzoxazinium chloride (253) with 1 and 2 mol of the appropriate heterocyclic quaternary salt 254 in the presence of a few drops of piperidine gave mono and bis condensation products 255 and 256, respectively (98MI45). Similar reactions of 2-arylpyrido[l,2,3- /e]-l,4-benzoxazinium bromides and 254 [R = R =-(CH=CH)2-] yielded condensation products 257 (X = 0). 

The reaction of cyclopropyl bromide with triphenylphosphine gives the expected phosphonium salt in less than 1 % yield. An alternate route to the salt by the thermal decomposition of 2-oxo-3-tetrahydrofuranyltriphenylphosphonium bromide gives a... 

This transformation can also be carried out under solvent-free conditions in a domestic oven using acidic alumina and ammoniiun acetate, with or without a primary amine, to give 2,4,5-trisubstituted or 1,2,4,5-tetrasubstituted imidazoles, respectively (Scheme 15A) [69]. The automated microwave-assisted synthesis of a library of 2,4,5-triarylimidazoles from the corresponding keto-oxime has been carried out by irradiation at 200 ° C in acetic acid in the presence of ammonium acetate (Scheme 15B) [70]. Under these conditions, thermally induced in situ N - O reduction occurs upon microwave irradiation, to give a diverse set of trisubstituted imidazoles in moderate yield. Parallel synthesis of a 24-membered library of substituted 4(5)-sulfanyl-lff-imidazoles 40 has been achieved by adding an alkyl bromide and base to the reaction of a 2-oxo-thioacetamide, aldehyde and ammonium acetate (Scheme 15C) [71]. Under microwave-assisted conditions, library generation time was dramatically re-... 

CN 1 -methyl-1 -[ 1 -methyl-2-oxo-2-( 10//-phenothiazin-10-yl)cthyl]pyrrolidinium bromide... 

A different multicomponent route to imidazoles has been described by the group of O Shea, involving the diversity-tolerant three-component condensation of an aldehyde, a 2-oxo-thioacetamide, and an alkyl bromide (5 equivalents) in the presence of ammonium acetate (Scheme 6.201) [364]. This allowed the preparation of a 24-membered 4(5)-alkylthio-lH-imidazole demonstration library from 21 different aldehydes, 12 alkyl bromides, and two 2-oxo-thioacetamides. The library was synthesized in a parallel format using a custom-built reaction vessel. Alkylthioimidazoles... 

A23-22-Oxo steroids 424 have been synthesized via 1,3-dipolar cycloaddition of steroidal nitrile oxides to low-molecular dipolarophiles. Cycloaddition of 2-propynyl bromide to 20-carbonitrile oxide, followed by hydrogenation of the isoxazole derivative, gives 22-enamino-24-keto steroid. The latter has then been converted into the target enones in several steps (465). 

Alternatively, l-oxo-l,2,3,4-tetrahydroquinolizinium ion (111 Scheme 73) and its congeners may be converted to derivatives of 1-hydroxyquinolizinium ion (63JCS2203). The bicyclic ketone (111) can be brominated to yield the 2-bromo (112) or the 2,2-dibromo derivative (113). Action of boiling acetic anhydride converts the monobromo ketone (112) to 2-bromoquinolizinium bromide (Table 2). If the same bromo ketone (112) is heated with ion-exchange resin (Amberlite IRA-400) loaded with hydroxyl ions or, alternatively, heated with silver acetate in water, the 1,2-dihydroxyquinolizinium ion is formed and may be recovered as the picrate (Scheme 74). 

Dimethyl-3-(2-oxo-2-phenyl-ethyl--bromid lagert sich beim Kochen mit Triethylamin in Acetonitril in 2-(2-Imino-5-phenyl-2,3-dihydro-oxazol-3-yl)-4,6-dimethyl-pyrimidin um. Aus diesem werden durch Kochen in Alkoholen mit 4-Methyl-benzolsulfonsaure als Katalysator 2-Alkoxy-l-(4,6-dimethyl-2-pyrimidyl)-4-phenyl-imidazole oder durch Erhitzen mit primaren oder sekundaren Aminen ebenfalls in Gegenwart von 4-Methyl-benzolsulfonsaure 2-Alkylamino-l-(4,6-dimcthyl-2-pyrimidyl)-4-phe-nyl-imidazole erhalten374 ... 

Br —CH2 —CO —CgH5 H5Cj-OH Ruckfl. 3-Amino-1-methyl-2- (2-oxo-2-phenyl-ethylthio J -benzimidazolium-bromid 85 120-125 366... 

Br-CH2-C-< J>-N02 ethyl)-2-methyl-3-[2- (4-nitro-phenyl) -2-oxo-ethyl. .. -bromid 412... 

---