Dihalo compounds

The same disconnection is also effective for cyclopropanes but the reagent for the earbene synthon is a diazocompound RCHN2 or a dihalo compound treated with a metal e.g. 

Treatment of geminal dihalocyclopropyl compounds with a strong base such as butyl lithium has been for several years the most versatile method for cumulenes. The dihalo compounds are easily obtained by addition of dihalocarbenes to double--bond systems If the dihalocyclopropanes are reacted at low temperatures with alkyllithium, a cyclopropane carbenoid is formed, which in general decomposes above -40 to -50°C to afford the cumulene. Although at present a number of alternative methods are available , the above-mentioned synthesis is the only suitable one for cyclic cumulenes [e.g. 1,2-cyclononadiene and 1,2,3-cyclodecatriene] and substituted non-cyclic cumulenes [e.g. (CH3)2C=C=C=C(CH3)2]. 

In addition to the trialkyldihalo- and triaryldihalo antimony compounds, mixed dihalo compounds such as chi oroiodo triphenyl antimony [7289-82-9], (CgH3)2SbClI, have been reported (182). It has been shown, however, that such compounds disproportionate ia solutioa to give a mixture of startiag material plus products (183) ... 

Trialkyl- and triaryldihaloarsoranes have been studied to a much greater extent than the tri- and tetrahaloatsotanes. The dihalo compounds ate stable crystalline species, although they decompose on heating ... 

The authors also reported a few polysulfides [54,55] caused the reaction between sodium sulfide and dihalo-compounds activated by —SO2— and amide groups, respectively. 

As a final example in this section, a contribution by Grubbs et al. is discussed. The chloride-free ruthenium hydride complex [RuH2(H2)2(PCy3)2] (37) is believed to react, in the presence of alkenes, to form an unidentified ruthenium(O) species which undergoes oxidative additions with dihalo compounds, e.g., 38, to give the corresponding ruthenium carbene complex 9 (Eq. 4) [20]. 

Other sources of Ru(0) can also be used for this synthesis. For example, it was recently demonstrated that [Ru(arene)(diene)] complexes such as 39 undergo double oxidative addition of heterosubstituted dihalo compounds 40 in the presence of phosphine ligands (Eq. 5) [21]. 

In other uses of ge/n-dihalo compounds, aldehydes and ketones add the CH2I group, R2CO —> R2C(OH)CH2l, when treated with CH2I2 in the presence of and the... 

Omission of the 17-hydroxyl group in the 6,9-dihalo compounds apparently does not lead to loss of biological activity. Dehydration of the 6a-fluoro-17-desoxy intermediate 272 by means of NBS in pyridine... 

On treatment with concentrated halogen acids, certain hexitols yield 1,6-dideoxy-l,6-dihalo compounds. The structure of the compound so obtained from galactitol, first reported by Bouchardat,404 was later verified by synthesis.405 Allitol is transformed406 into 1,4-anhydro-6-chloro-6-deoxy-DL-allitol and l,4-anhydro-5,6-dichloro-5,6-dideoxy-DL-talitol on treatment with fuming hydrochloric acid at 100°. 

The dihaloalkanes having the same type of halogen atoms are named as alkyUdene or alkylene dihalldes. The dihalo-compounds having same type of halogen atoms are further classified as geminal halides (halogen atoms are present on the same carbon atom) and vicinal halides (halogen atoms are present on the adjacent carbon atoms). In common name system, pem-dihalides are named as aUq Udene halides and uic-dihalides... 

Molina et al. were able to prepare the mesoionic thiadiazole (292) from iminophosphorane 297 and carbon disulfide. As Scheme 106 shows, 298 reacts with a,w-dihalo compounds to form dimer 299 [91JCS(P1)1159]. The synthesis of the mesoionic thiazolo[2,3-6][l,3,4]thiadizole is described in (92T1285). 

Several pyrazolo[l,2-a]pyrazoles are prepared by alkylation of pyrazoles with 1,3-dihalo compounds or with malonyl chloride (66FRP1441519 82LA420 86AP70). For example, treatments of 183 with disubstituted malonyl chlorides afford 184. Very similar to this is the formation of pyrazolo[l,2-a]-pyrazolium bromide from 1/f-pyrazoles and bromomethyloxirane (71JHC489 79JOC4473). 

It is difficult to obtain cross-coupling products of two different carbonyl compounds by an intermolecular version of the McMurry reaction. Examples that use excess amounts of one carbonyl component are few. "" When one carbonyl component is replaced by a 1,1-dihalo compound or dithioacetal and the alternative is reduced with a low-valent metal such as low-valent titanium or chromium(ii), cross-coupling products, that is, Wittig-type olefins, are produced in high yields. Because the alternative approach is described elsewhere, we concentrate on only its important features here. 

Third, chromium-based reagents prepared by reduction of 1,1-dihalo compounds with CrCl2 are suitable for the transformation of aldehydes to (i4)-iodoalkenes, (it)-alkenylsilanes, " and ( )-alkenylboronic esters with one-carbon homologation (Equation (8)). The amount of CrCl2 can be reduced to a catalytic amount by using manganese (or zinc) and MesSiCl. " ... 

Vicinal dihalo compounds, dehalogena-tion of, 7-10 Vinyl amines, 98 Vinyl ammonium hydroxides, 97 Vinyl azides, 277 Vinyl carbazole, 98 V-Vinyldimethylamine, 103 Vinylidene chloride, reaction with sodium /8-alkoxyalcoholates, 56, 58... 

They also developed a second process via other dihalo-compounds [36]. Treatment of the 1,2-bromo-hydroxy chain with TiCl4 in DME, gave mainly the l-bromo-4-chloro unit. Condensation with the Ci0 sulfone in DMF, in the presence of /BuOK gave the retinyl-sulfoneacetate. Elimination of the tolylsulfmate with KOH in DMF produced vitamin A acetate in 87% yield, Fig. (14). 

The most direct synthesis is performed by reaction of a dihalo compound with a tricoordinated phosphorus compound including a reactive P—Y bond (reaction 101). This synthesis, first used with secondary phosphines, the corresponding phosphides or diphosphines (Y = H, Na, K, PPh2)2b,38°, has subsequently been developed also with silylphosphines (Y = SiMe3),132,381-383 which are easier to handle (reaction 102). The same kind of cyclization by intramolecular alkylation can be achieved using a functional phosphine prepared in a multi-step synthesis380,384,385 (reaction 103). 

The reaction of a diphosphine with a dihalo compound, resulting in the formation of a di- or tetra-phosphonium salt2c, is a special case because if fits well with a cyclization on phosphorus, but also at the same time with a cyclization between two chains already linked to the second phosphorus (reaction 102). Another kind of ring closure on the phosphorus results from the biphilic character of halophosphines toward dienic392 or acetylenic28,393 systems (reaction 105). 

Dihalo compounds react with thioureas or thioamides (77HCA2872, 75CPB1764, 73RTC20) syntheses of 2,4-benzothiazepines, e.g. (322) and (324), from o-xylyl dibromides (323) are shown, o-Chloromethylbenzoyl halides similarly give 2,4-benzothiazepin-5-ones and 4-bromobutyryl chloride gives the 1,3-benzothiazepin-4-one system. 

Depending on the molar ratio, halogenation of 4-oxo-6,7,8,9-tetra-hydro-4//-pyrido[l,2-n]pyrimidines gave 9-halo or 9,9-dihalo compounds.75,133,316-319 9-Bromo- or 9-chloro-6-methyl-4-oxo-6,7,8,9-tetra-hydro-4if-pyrido[l,2-a]pyrimidine-3-carboxylic acids were obtained as 4 1 mixtures of the thermodynamically more stable 6,9-diaxial and the 6-axial, 9-equatorial-substituted diastereoisomers.317... 

Another useful procedure for the synthesis of dioxepins, oxathiepins, as well as dithiepins under basic conditions involves deprotonation of a diol or dithiol precursor and treatment of the resulting anion with a g and biaryl derivative 132 <2005TL7291> (Scheme 62) ... 

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