Methyl selective chlorination with

Many other glycosides have been subjected to selective chlorination with sulfuryl chloride. Methyl /3-L-arabinopyranoside afforded methyl 4-chloro-4-deoxy-a-D-xylopyranoside 2,3-di(chlorosulfate) in 29% yield, whereas the a-L anomer gave357 methyl 3,4-dichloro-3,4-dideoxy-/3-i)-ribopyranoside 2-(chlorosulfate) (30%). Methyl /3-d-ribopyranoside was converted into methyl 3,4-dichloro-3,4-dideoxy-a-L-arabinopyranoside through the action of pyridine hydrochloride on its 2,3,4-tri(chlorosulfate).358 Methyl a-D-lyxopyranoside gave only the 2,3,4-tri(chlorosulfate),353 as would be expected from the disposition of its hydroxyl groups, similar to that in the rhamno- and manno-pyranosides. Methyl a-D-altropyranoside was transformed into the 6-chloro-6-deoxy 2,3,4-tri(chlorosulfate) derivative in 80% yield.353... 

Treatment of pyrrole, 1-methyl-, 1-benzyl- and 1-phenyl-pyrrole with one mole of A -bromosuccinimide in THF results in the regiospecific formation of 2-bromopyrroles. Chlorination with IV-chlorosuccinimide is less selective (8UOC2221). Bromination of pyrrole with bromine in acetic acid gives 2,3,4,5-tetrabromopyrrole and iodination with iodine in aqueous potassium iodide yields the corresponding tetraiodo compound. 

Morphology of the anionically synthesized triblock copolymers of polyfp-methyl-styrene) and PDMS and their derivatives obtained by the selective chlorination of the hard segments were investigated by TEM 146). Samples with low PDMS content (12%) showed spherical domains of PDMS in a poly(p-methylstyrene) matrix. Samples with nearly equimolar composition showed a continuous lamellar morphology. In both cases the domain structure was very fine, indicating sharp interfaces. Domain sizes were estimated to be of the order of 50-300 A. 

Richardson and Hough s efforts on the chlorination of sucrose ran in parallel with their studies on the selective chlorination of other readily available disaccharides. One notable piece of work done with Philippe L. Durette involved a study of the regioselective chlorination of methyl (S-maltoside (Scheme 31), which was undertaken with the long-term objective of possibly developing a future synthesis of the natural antitumor agent, amicetin. 

SCHEME 31. Durette, Hough, and Richardson s study of the selective chlorination of methyl p-maltoside with sulfuryl chloride (1973). 

R. S. Bhatt, L. Hough, and A. C. Richardson, Selective chlorination of methyl p-lactoside with mesyl chloride in DMF, Carbohydr. Res., 49 (1976) 103-118. 

Chalcose (4,6-dideoxy-3-0-methyl-D-xy/o-hexose, 152) was obtained from methyl 4,6-dichloro-4,6-dideoxy-a-D-galactopyranoside (164).240 The dichloride 164 was readily prepared by selective chlorination of methyl ot-D-glucopyranoside with... 

For electrophilic and more bulky radicals, for example CnHal2n+i, selectivity increases dramatically. Whereas the selectivity for the radical chlorination (Table 1, entry 7) and bromination (Table 1, entry 8) of adamantane with Hal2 in CC14 is only approximately 5, for chlorinations with CC14 (Table 1, entries 9 and 10) and brominations with BrCCl3 (Table 1, entry 11) the selectivity increases to 21.5-27. Halogenations under metal-catalyzed GIF conditions (Table 1, entry 12) or in the presence of dioxirane (Table 1, entry 13) are less selective, because of the participation of oxygen-centered (GIF) or methyl (DMD) radicals. 

A convenient way selectively to introduce a chlorine atom into the methyl group of a methyl ketone has been developed. It involves treatment of the imine, formed from the reaction of the methyl-keto-group with ethanolamine, with Af-chlorosuccinimide (see Part II, Chapter 1, ref. 311 and also refs. 149-151 and 156). Various 3-trifluoromethyl derivatives have been prepared by photolytic addition of trifluoroiodomethane across the A -double-bond. ... 

Chlorination of Aromatic Compounds. NCS has also been used for the chlorination of pyrroles and indoles however, the reaction is less straightforward than when NBS and N-Iodosuccinimide are used. In the chlorination of 1-methylpyrrole, it has been demonstrated that basic conditions (NaHCOs, CHCI3) lead to the formation of 1-methyl-2-succinimidylpyrrole (eq 11). In the presence of catalytic amounts of perchloric acid, thiophenes and other electron-rich aromatic compounds have been chlorinated with NCS. (N-Chlorosuccinimide-Dimethyl Sulfide is used for the selective -substitution of phenols.)... 

Ando et al. 292,293 sported a series of chlorin dimers 341 and trimers 342 joined by amide bonds and found that among such oligomers, dimer 341 (Scheme 71) did show good tumor uptake and selectivity compared with the hematoporphyrin derivative (HpD). As part of their effort to improve the in vivo antitumor activity of chlorin-based photosensitizers, Pandey et extended this approach for the preparation of a series of amide-linked symmetrical and unsynunetrical chlorin dimers 345-347 (Scheme 72). For the preparation of unsymmeuical dimo 349, methyl pheophorfoide a was reacted with 1,3-propanediamine and the intermediate amide 345 was isolated in 80% yield. Reaction of 348 with H2(HPPH) afforded the unsymme-ttical dimer in 70% yield, and was found to be effective in... 

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