Geminal dichloride

An interesting formation of a 1,3-dioxan -one from a geminal dichloride and salicylic acid is displayed in Scheme 103. Langer et al. have found that phthaloyl chloride cleanly reacted with salicylic acid. The product was not the expected nine-membered ring but spirotetracycle 219 in 82% yield. The product formation can be explained by assuming an initial equilibration of phthaloyl chloride and 3,3-dichloro-3//-isobenzofuran-l-one <2001EJ01511>. 

For the dichlorobutanes the two Cl s are first placed on one C of the straight chain. These are geminal or gem-dichlorides. 

Condensation Reactions. Many triam inotriarylmethane dyes can be produced by condensation of Michlers ketone (9) with aromatic amines. The ketone must generally be activated with phosgene or phosphorus oxychloride, whereby a reactive blue chloro compound (10) is formed from the intermediate geminal dichloride. With V-phcnyl-1 -naphthylaminc, for example, (13) reacts to form Victoria blue B (11). 

The first system to be studied was 2-methyl-2-tolyl-cyclopentanone 168. In early 1979 we attempted to perform direct geminal dimethylation of this compound using dimethyltitanium dichloride 17114 in hope of obtaining curparene (Sect. F.II). Initial attempts were unsuccessful, since the product turned out to be the Grignard-type adducts 169 and 170 (Equation 57). 

Another reaction which can be brought about by PCI5 is the conversion of aldehydes and ketones into the corresponding geminal dichlorides and this is illustrated in Protocol 7 by the conversion of terephthalaldehyde 36 into the tetrachloride 37. Unusually for a reaction using PCI5, no HC1 is evolved here and the product is sufficiently unreactive to be isolated using an aqueous work-up. It should be noted that chlorination of aromatic aldehydes in this way is the method of choice for synthesis of benzylidene chlorides since the products obtained from the alternative chlorination of toluenes are always contaminated by the benzyl chlorides and benzotrichlorides. 

A variation of this reaction was developed in 1986 by Takai and Utimoto, in which geminal dihaloalkanes were added to aldehydes in a reaction mediated by chromium dichloride. This led to the stereoselective formation of the corresponding tran5-olefins 10 [12]. The major drawback of this method is the rather cumbersome access to the corresponding substituted dihalomethane compounds, which prevents a broad application of this reaction for synthesis. 

If the reaction is carried out with anhydrous hydrogen fluoride replacing the Lewis acid, a mixture of geminally dihalogenatcd compounds is obtained gem-dichlorides 7, gpm-chlorofluo-rides 8 and getn-diiluorides 3 (Table 7). ... 

Although mixtures of halogenated compounds are obtained, and good procedures for the synthesis of gem-dichlorides and difluorides are known, this reaction can be useful for the preparation of gem-chlorofluoroalkanes. Only very few examples of synthetic procedures for these particular mixed geminally dihalogenated compounds are known. 

The trimeric phosphazene dichloride, hexachloro-cyclotriphosphazene (N3P3Clg), reacts with dilithium l,T-ferrocenylene dichalcogenates, fc(ELi), under stepwise replacement of the three pairs of geminal chloro substituents to give spiro-cyclotri-... 

Scheme 5) are accessible by nucleophilic elimination-cycloaddition of geminal dichlorides with the anions [(OC)4MnPPh2] and [(i/ -C5H5)Mo(CO)2PPh2] respectively. 

Geminal The two groups under consideration are attached to the same carbon atom, e.g. a geminal dichloride, -CC12- See also vicinal. 

The direct geminal dimethylation of ketones using dimethyltitanium dichloride has provided an extremely simple synthesis of cuparene (120) from the ketone (121).77 This efficient procedure should prove useful in other sesquiterpenoid syntheses in view of the fact that the gem-dimethyl group is a common feature in a number of such compounds. A new sesquiterpene, (—)-herbertene (122), has been... 

Treatment of ketones wifh a mixture of CH2I2, TiCl4, and zinc in THF at 0°C for 90 min produced fhe mefhylenation product in 5-8% yield whereas when lead dichloride was added the reaction proceeded smoothly at 0 °C to give the product in 81% yield wifhin 30 min (Scheme 13.68) [85]. A catalytic amount of lead dichloride probably promotes furfher reduction of zinc carbenoid (ICH2ZnI) by zinc in THF to give a geminal dizinc compound (CH2(ZnI)2) which is a key intermediate for the methylenation of carbonyl compounds. 

The halogen atoms of the geminal dihalo derivatives of diaryl diketones and of heterocyclic ketones can be replaced in reactions with sulfur compounds 0e.g., sodium hydrogen sulfide, thioacetic acid, phosphorus pentasulfide), thioketones being formed.318,319 Staudinger and Freudenberger,320 for instance, obtained thiobenzophenone in 46% yield from benzophenone dichloride (dichlorophenylmethane) and a hot alcoholic solution of sodium hydrogen sulfide ... 

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