Anhydro cleavage

Alkylation of the anhydro-bases derived from 3,4-dihydro-jS-carboline and l-methyl-3,4-dihydro-)5-carbohne takes place at the pyr-N and is accompanied by ring cleavage. It was beheved that alkylation of the anhydro-bases derived from 7-methoxy-l-methyl-3,4-dihydro-jS-carboline alkiodides occurred at the pyr-N to give quaternary salts of type 458. It has now been shown, however, that methylation of the anhydro-base 438b (R = CH3) actually gives the... 

Benzothiazoline, cleavage of ring, 42 polarizabilite of CS bond, 42 Benzothiazolium salts, action on anhydro-base, 43... 

Table I. Ring Cleavage of 5,6-Anhydro-isopropylidene-D-glucof uranose.. 68...

An interesting contrast has been observed between the respective actions of acid and alkali on 3,4-anhydro-l,2-isopropylidene-D-tagatose (XXIVo). The anhydro ring of this compound shows considerable resistance to both mineral acids and alkali. Cleavage by sodium meth-... 

In their pioneering work. Just and co-workers have described many interesting transformations of the Diels-Alder adducts of furan to methyl nitroacrylate (77 + 77 ) and to dimethyl acetylenedicarboxylate (53). The mixture of racemic adducts 77 + 77 was hydroxylated into the exo-cis-diols 125 + 125 , separable by crystallization. Treatment of the isopropylidene acetal obtained from 125 with diazabicyclo[5.4.0]undec-5-ene (DBU) gave a high yield of alkene 126. Ozonolysis followed by a reductive work-up with dimethylsulfide, then with NaBH4, gave a mixture of epimeric triols 127. Cleavage with sodium periodate afforded 2,5-anhydro-3,4-0-isopropylidene-DL-allose (128) in 15 % yield, based on methyl 2-nitroacrylate used. TTie same allose derivative was obtained from adduct 53. ... 

Despite the fact that secondary hydroxyl groups of nucleosides also react with 23 (see later), selective iodination of only the primary hydroxyl group in some unprotected, pyrimidine nucleosides can also be achieved.82 Thus, brief treatment of thymidine with 1.1 mol-equivalents of 23 in N,N-dimethylformamide gave crystalline 5 -deoxy-5 -iodothymidine in 63% yield. It was even possible to effect some selective iodination of the 5 -hydroxyl group of 2,2 -anhydrouri-dine without excessive cleavage of the (quite labile) anhydro linkage. 

For 2,3-anhydro-/3-D-ribopyranosides, the normal mode of cleavage leads to 3-substitution, giving D-xylo derivatives. This result implies... 

Cleavage of the dithioacetal groups from the products, followed by reduction of the resultant carbonyl derivatives (46, 49, 52) with sodium borohydride leads,68 with the three compounds (45, 48, and 51), to 1,4-anhydro-L-ribitol (2,5-anhydro-D-ribitol) (47), 1,4-anhydro-L-xylitol (2,5-anhydro-D-xylitol) (50), and 1,4-anhydro-D-arabinitol (2,5-anhydro-D-lyxitol) (53), identified by comparison with their enantiomorphs, 1,4-anhydro-D-ribitol,69 1,4-anhydro-D-xylitol,70 and 1,4-anhydro-L-arabinitol. 71... 

Christensen and Goodman20 4 have carried out the cleavage of methyl 2,3-anhydro-4,0-c-benzylidene-a-D-allc)flide with alkaline benzyl mercaptan. Attack takes place at C[Pg.446]

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