3- chloro-4- -2-butanone

Write the structures of the enol forms of 2 butanone that react with chlorine to give 1 chloro 2 butanone and 3 chloro 2 butanone... 

Reaction of isatins with 3-chloro-2-butanone gave 205.9 l-(o-Tolyl)-isatins underwent a reaction similar to the Pfitzinger synthesis to give 206.71... 

Related methods. The replacement of 3-chloro-2-butanone (or of similar a-halogenated ketones) by ethyl a-chloroacetoacetate [Graffenried and Kostanecki, 1910) gives aryloxyacetoacetates (77)]. Cyclodehydration of esters (77) (with H2S04) gives good yields (60-70%) of coumarilic esters (78),232 which are sometimes difficult to synthesize by other methods. 

As shown in the general equation and the examples, halogen substitution is specific for the a-carbon atom. The ketone 2-butanone has two nonequivalent a carbons, and so substitution is possible at both positions. Both l-chloro-2-butanone and 3-chloro-2-butanone are formed in the reaction. 

Butanone Chlorine 1 -Chloro-2-butanone 3 -Chloro- 2-butanone... 

Reaction of N-substituted bromomethanesulfonamides with 2 equiv of potassium carbonate and an cr-haloketone, ester, or nitrile leads directly to the /3-sultams 187 substituted at the C-3 position by an EWG. This base-promoted condensation can be used with a-halo ketones, esters, and nitriles where a second Sn2 intramolecular displacement can operate in tandem fashion (Scheme 60). This domino alkylation sequence exhibits a reactivity order where ketone > nitrile > ester (Table 14). The process is particularly efficient when diethyl bromomalonate or 3-chloro-2-butanone are involved <2004CJC113>. 

There are also examples of the use of compounds that are converted into diketones under the conditions of the Pfitzinger reaction and then react with isatins. Thus, the diacid 56 (yield 58%) was obtained from 2-hydroxy-3-butanone and isatin 7 in the presence of potassium hydroxide in water [26], while the dicarboxylic acids 58 were synthesized from 3-chloro-2-butanone and isatins 57 [44], The initial chloro ketone is clearly saponified to 2-hydroxy-3-butanone under the reaction conditions. As in the reaction with isatin 7, the product is then oxidized to 2,3-butanedione, which reacts with two molecules of isatin. 

Other factors. The roaatifHi with aJdehydes usually takes place tween 0 and 15° in a solvent such as ether or acetone in the cases mentioned abovo, or in jS-lactone itself if the procesa is con-tinuoua.i T Cyclohexanone reacts in ether solution between -10 and 0 , For the reaction with other ketones, which if present In excess serve as the solvent, keteno ie often added at room tempera tnre. This ia true also for the <]uiuoneH. < Ocarnforth studied the stereceolectivity of the addition of ketene to 3-chloro-2-butanone. 

Other halogenated ketones for which photolysis studies have been reported are 3-chloro-2-butanone and 4-chloro-2-butanone , perfluorocyclobutanone , di-chloromethyl and trichloromethyl cyclohexadienones , and bromodiketones . 

The reaction between a-halo ketones and sodium dialkyl phosphites has been extended to phosphonate carbanions. For example, diisopropyl 1 -lithio-1-fluoromethylphosphonate, generated from diisopropyl fluoromethylphosphonate and LDA, reacts with 3-chloro-2-butanone at low temperature in THF to give diisopropyl l-fluoro-2-nicthyl-2,3-cpoxybutylphosphonate in 46% yield. 33.134... 

The topicity concept is also important in the reactions of trigonal centers, such as carbonyls and alkenes. In consideration of carbonyls, for example, the two faces are homotopic in a symmetrically substituted ketone, such as acetone or 2-pentanone, because the molecule has C2 symmetry. However, the faces are enantiotopic in an unsymmetrically substituted ketone, such as 2-butanone 190. While the reaction with hydride ion on the top face of the carbonyl group forms (M)-2-butanol 191, the reaction on the bottom face forms (5)-2-butanol 192. Extending this argument further, the two faces are diastereotopic in an unsymmetrical ketone bearing a chiral center elsewhere in it, e.g., (7 )-3-chloro-2-butanone 193. The delivery of hydride ion to the top face of the carbonyl group forms 2(/ ),3(/f)-3-chloro-2-butanol 194 and the delivery to the bottom face forms 2(,S ),3(A )-3-chloro-2-butanol 195. The molecules 194 and 195 are diastereoisomers. 

Another common situation where topicity issues become important is at trigonal centers, such as carbonyls and alkenes. As some examples, let s focus on carbonyl groups. The two faces of the carbonyl are homotopic in a ketone substituted by the same groups [R(C=0)R], such as acetone, because the molecule contains a C2 axis (see below). The faces are enantiotopic in an unsymmetrically substituted ketone, such as 2-butanone, because they are interconverted by a a plane. The faces are diastereotopic in a structure such as either enantiomer of 3-chloro-2-butanone, because there are no symmetry elements that interconvert the faces. 

Consider the three ketones in Figure 6.7 and the topicities of their carbonyl faces. In acetone, the two faces of the carbonyl are homotopic—interconverted by a C2 rotation. In 2-butanone, the faces are enantiotopic (prochiral)—interconverted only by a mirror plane. In (R)-3-chloro-2-butanone, the two faces are diastereotopic. This molecule is asymmetric, and so there can be no symmetry operation that interconverts the two faces of the carbonyl. A consequence of this lack of symmetry in (R)-3-chloro-2-butanone is that the carbonyl group is expected to be nonplanar—that is, O, C2, Cl, and C3 will not all lie in a plane. The point is that because the two faces of the carbonyl are inequivalent, the carbonyl cannot be planar. This is a symmetry argument of the sort mentioned previously, and as with all symmetry arguments, we cannot predict how large the deviation from planarity must be, only that it is expected to be there. As such, if we obtain a crystal structure of (R)-3-chloro-2-buta-none, we should not be surprised to find a nonplanar carbonyl. 

As we can anticipate the stereochemical relationships among the products, we can also evaluate the symmetry properties of the transition states of the hydride addition reactions. For acetone, there is only one possible transition state and only one product. For 2-butanone, the transition states derived from "top" and "bottom" attack are enantiomeric. As such they will have equal energies, and so AG will be the same for the formation of the two enantiomeric products. As a result, a racemic mixture must form. Finally, in the reduction of (R)-3-chloro-2-butanone, the two transition states are diastereomeric, and so they are expected to have different energies (diastereomers differ in all ways). Since the starting point for the two reactions is the same, AG is expected to be different for the two, and therefore the rates for formation of the two diastereomeric products cannot be the same. Since the rates of formation of the two products are not the same, we can state with certainty that the reduction of (R)-3-chloro-2-butanone is expected to not produce a 50 50 mixture of the two products in the initial reaction. This can be anticipated from first principles. When we start from a single reactant and produce two diastereomeric products, we do not expect to get exactly a 50 50 mixture of products. However, as is always true of a symmetry argument, we cannot anticipate how large the deviation from 50 50 will be—it may be 50.1 49.9 or 90 10. We can only say that it is not 50 50. 

Another example of a stereoselective reaction is the previously discussed reduction of (R)-3-chloro-2-butanone (see Figure 6.7). In this case the two products are diastereomers, and the reaction is referred to as diastereoselective. This reaction is also stereospecific, in that (S)-3-chloro-2-butanone will give a different ratio of products with the same reducing agent. If the two products are enantiomers [as in the reduction of 2-butanone (Figure 6.7)], the reaction is enantioselective if one enantiomer is formed preferentially. 

For the wheat fungicide silthiofam (E), an efficient low-cost synthesis has been developed, which starts from 3-chloro-2-butanone (X) and proceeds via the following steps ... 

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