Dibromide synthesis

The useful ring closure providing benzothiepines involved the formation of both S-C bonds by reaction of diaryllithium or divinyllithium organometallic species with S2+ equivalents. Another method for formation of both S-C bonds toward dihydro- and tetrahydrothiepines and thiepines is the nucleophilic substitution reaction of S2 equivalents (Na2S or Li2S) with dibromides. Synthesis of thiepines by the related stepwise formation of two S-C bonds was also described. 

Merrilactone A, via ring-closing diene metathesis, 11, 210 Mesitylato complex, with Pd, 8, 347 Mesitylbismuth dibromide, synthesis, 3, 916 Mesitylbismuth dichloride, synthesis, 3, 916 Mesitylcopper complex, characteristics, 2, 157... 

P. M. Lahti, A. Sarker, R. O. Garay, R. W. Lenz, and F. E. Karasz, Polymerisation of 1,4-bis(tetrahy-drothiopheniomethyl) - 2 - cyano - 5 - methoxybenzene-dibromide synthesis of electronically push-pull" substituted poly(p-phenylene vinylene)s. Polymer 55 1312 (1994). 

Ambrettohde is obtained from hibiscus and has a musk like odor Its preparation from a compound A is outlined in the table that follows Write structural formulas ignonng stereochem istry for compounds B through G in this synthesis Hint Zinc as used in step 4 converts vici nal dibromides to alkenes )... 

Titanium Dibromide. Titanium dibromide [13873-04-5] a black crystalline soHd, density 4310 kg/m, mp 1025°C, has a cadmium iodide-type stmcture and is readily oxidized to trivalent titanium by water. Spontaneously flammable in air (142), it can be prepared by direct synthesis from the elements, by reaction of the tetrabromide with titanium, or by thermal decomposition of titanium tribromide. This last reaction must be carried out either at or below 400°C, because at higher temperatures the dibromide itself disproportionates. 

Ceroplastol synthesis, 1, 428 Cetyl alcohol synthesis, 1, 478 Chaetoglobasins structures, 4, 376 Chalcone, o -azido-2 -oxy-synthesis, 3, 823 Chalcone, 2-hydroxy-reduction, 3, 751 Chalcone, 2 -hydroxy-mass spectra, 3, 618 Chalcone dibromides flavone synthesis from, 3, 823 Chalcones polymers, 1, 304 Chanoclavine synthesis, 6, 423 Charge density waves in stacks of ions, 1, 351-352 Chartreusin... 

In the early 1930 s, when the prime research aim was the commercial synthesis of the sex hormones (whose structures had just been elucidated), the principal raw material available was cholesterol extracted from the spinal cord or brain of cattle or from sheep wool grease. This sterol (as its 3-acetate 5,6-dibromide) was subjected to a rather drastic chromic acid oxidation, which produced a variety of acidic, ketonic and hydroxylated products derived mainly by attack on the alkyl side-chain. The principal ketonic material, 3j -hydroxyandrost-5-en-17-one, was obtained in yields of only about 7% another useful ketone, 3 -hydroxypregn-5-en-20-one (pregnenolone) was obtained in much lower yield. The chief acidic product was 3j -hydroxy-androst-5-ene-17j -carboxylic acid. All three of these materials were then further converted by various chemical transformations into steroid hormones and synthetic analogs ... 

For synthesis of the parent isoindole, Kreher and Seubert used the condensation of theo-xylene dibromide (23) with 0-benzylhydroxyl-amine (24) to give 2-henzyloxyisoindoline (25). Elimination occurred 25 A. H. Blatt, Chem. Rev. 27, 429 (1940). 

This method is similar to that employed in the synthesis of isoselenazoles (73JHC267). However, owing to the thermal stability of the tellurium dibromides 6, one can perform the reaction at room temperature, whereas with selenium dibromides it must be carried out at -70°C. 

In a modified procedure the free carboxylic acid is treated with a mixture of mercuric oxide and bromine in carbon tetrachloride the otherwise necessary purification of the silver salt is thereby avoided. This procedure has been used in the first synthesis of [1.1.1 ]propellane 10. Bicyclo[l.l.l]pentane-l,3-dicarboxylic acid 8 has been converted to the dibromide 9 by the modified Hunsdiecker reaction. Treatment of 9 with t-butyllithium then resulted in a debromination and formation of the central carbon-carbon bond thus generating the propellane 10." ... 

Cyclization of the two pendant alkyl side chains on barbiturates to form a spiran is consistent with sedative-hypnotic activity. The synthesis of this most complex barbiturate starts by alkylation of ethyl acetoacetate with 2-chloropentan-3-one to give 152. Hydrolysis and decarboxylation under acidic conditions gives the diketone, 153. This intermediate is then reduced to the diol (154), and that is converted to the dibromide (155) by means of hydrogen bromide. Double Internal alkylation of ethyl... 

Palladium-mediated catalysis has only been exploited relatively recently in the synthesis of substituted PPV derivatives. The use of aryl dibromides as monomers is particularly useful as it allows the synthesis of PPVs substituted with alkyl rather than alkoxy sidechains. The Suzuki [53, 54], Heck [55], and Stille [56] reactions have been used in the synthesis of new PPV derivatives, but attaining high molecular weight PPV derivatives by these methodologies has proved problematic. A phenyl-subslilutcd PPV material PPPV 31 was synthesized by a Suzuki coupling (Scheme 1-10) of dibromoethene and fo/.v-boronic acid 30. Its absorption (2ni ix=385 nm) and emission (2max=475 nm) maxima were strongly... 

For the preparation of 3-benzothiepin 3,3-dioxide (11) a multiple-step synthesis has been described.82 Oxidation of 4,5-dihydro-3-benzothiepin-l(2//)-one to its S,S-dioxide with hydrogen peroxide in glacial acetic acid, is followed by the multiple-step preparation of dibromide 10, which is dehydrohalogenated by triethylamine to provide sulfone 11. 

The enzymatic conversion of a-(aminomethyl)pyrroles is also used by nature to produce porphyrinogens like uroporphyrinogen III (see introduction, compound 8), which is the key building block in the biosynthesis of all known porphinoid natural products. This biomimetic method is a powerful tool for the synthesis of different porphyrins, e.g. for the preparation of JV,Af, V ,Ar"-tetramethylporphyrin-2,3,7,8,12,13,17,18-octaacetic acid dibromide 12.36... 

Chalcone dibromides are advantageous intermediates for the preparation of various nitrogen-containing heterocycles (refs. 1-4). In the case of exocyclic a,P-unsaturated ketones, however, only few examples are known concerning the utilization of their dibromides for such purposes (ref. 5). Our aim was, therefore, the synthesis of the dibromides of various exocyclic a,P-unsaturated ketones (ref. 6) and to study their chemical transformations. In our present paper the reaction of such dibromides with azide nucleophile is reported. 

The exocyclic a,P-unsaturated ketones la-h used for the preparation of dibromides 2a-h were E isomers synthesized by known procedures (refs. 7,8). Previously we reported the synthesis of some dibromides (2a,d,g) used here as starting materials, by the bromine addition of the appropriate a,P-unsaturated ketones (la,d,g) (ref. 6). In the case of our present study, compounds lb,c,e,f,h were allowed to react with a small excess of bromine in carbon tetrachloride solution at room temperature for approx. 20 min. to afford the dibromides 2b,c,e,f,h (Eqn. 1) (Table 1). 

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