Acid cleaving

A special problem arises in the preparation of secondary amines. These compounds are highly nucleophilic, and alkylation of an amine with alkyl halides cannot be expected to stop at any specifle stage. Secondary amides, however, can be monoalkylated and lydrolyzed or be reduced to secondary amines (p. 11 If.). In the elegant synthesis of phenyl- phrine an intermediate -hydroxy isocyanate (from a hydrazide and nitrous acid) cyclizes to pve an oxazolidinone which is monomethylated. Treatment with strong acid cleaves the cyclic irethan. 

Section 15 12 Periodic acid cleaves vicinal diols two aldehydes two ketones or an aldehyde and a ketone are formed... 

Hydrogen bromide adds to acetylene to form vinyl bromide or ethyHdene bromide, depending on stoichiometry. The acid cleaves acycHc and cycHc ethers. It adds to the cyclopropane group by ring-opening. Additions to quinones afford bromohydroquinones. Hydrobromic acid and aldehydes can be used to introduce bromoalkyl groups into various molecules. For example, reaction with formaldehyde and an alcohol produces a bromomethyl ether. Bromomethylation of aromatic nuclei can be carried out with formaldehyde and hydrobromic acid (6). 

Propanediol, acetone. This method removes the boronate by exchange. 2-Methylpentane-2,5-diol in acetic acid cleaves a phenyl boronate (85% yield). 

Furin, also known as paired basic amino-acid-cleaving enzyme (PACE), is a membrane bound subtilisin-like serine protease of the irons Golgi compartment. It is ubiquitously expressed and mediates processing of many protein precursors at Arg-X-Lys/Arg-Arg sites. 

Oxidation with chromium trioxide in acetic acid cleaved the indole ring to produce intermediate 23 which cyclodehydrated to give prazepam (24). 

Comparative sequence analysis based on MALDI-TOF-MS analysis of nucleic acids cleaved at specific bases and reference sequences used to construct in silico cleavage patterns enable cross-correlation of theoretical and experimental mass signal patterns. Observed signal pattern differences are indicators of sequence variations and... 

A Weak Lewis Acid Cleaves the C-F Bond. How Was the Glycosyl Fluoride Method Discovered 36... 

Most HPLC instruments monitor sample elution via ultraviolet (UV) light absorption, so the technique is most useful for molecules that absorb UV. Pure amino acids generally do not absorb UV therefore, they normally must be chemically derivatized (structurally altered) before HPLC analysis is possible. The need to derivatize increases the complexity of the methods. Examples of derivatizing agents include o-phthaldehyde, dansyl chloride, and phenylisothiocyanate. Peptides, proteins, amino acids cleaved from polypeptide chains, nucleotides, and nucleic acid fragments all absorb UV, so derivatization is not required for these molecules. 

The interaction of phenylbiguanide and ethyl p-ethoxypropionate in the presence of sodium methoxide yields a readily dissociable molecular complex of the expected guanamine and phenylbiguanide 486) (CLXIX). Aqueous picric acid cleaves the complex into the picrates of its constituents. However, the complex is not formed from the pre-formed 2- -ethoxyethyl-6-phenylguanamine (or its methyl analogue) and phenyl-biguanide in methanol or acetonitrile, and its nature is not completely understood (see also ref. 605). 

Sodium hydrogen sulphite,hypophosphorous acid and concentrated hydrobromic acid cleave 3-oxo-2,3-dihydrobenzoteUurophenes. 

Structures 16, 2 (R -R = Me), ° 4, if and 137, are all converted to the corresponding hydantoins by aqueous or methanolic hydrochloric acid, but it is possible to achieve selective hydrolysis. Thus, with aqueous ethanoic acid, 4 yields 148 (64%), whereas methanolic chloroethanoic acid cleaves 115 to 149(86%) the salt 137 gives 150 in aqueous methanol. ° ... 

A benzazepine that includes the same (3-ketoamide array as piroxicam (Chapter 11) retains NSAID activity. Oxidation of benzothiapinone (5-1), obtainable by cycli-zation of 4-(4-chlorophenylthio)-butyric acid, with hydrogen peroxide gives the corresponding sulfone (5-2). This is then converted to its enamine (5-34) by reaction with pyrrolidine. Condensation of the intermediate with 3,4-dichorophenylisocyanate (5-4) leads to the amide (5-5). Hydrolysis with an aqueous acid cleaves the enamine function to give the keto-amide and thus enolicam (5-6) [6]. 

The 3-amino isomers are more resistant towards reduction 3-amino-5-phenyl-l,2,4-thiadiazole is not affected by hydrogen sulfide or acidified potassium iodide, but does undergo decomposition under the influence of stannous chloride in acids or sodium in alcohol.126 Zinc in hydrochloric acid cleaves the heterocyclic nucleus completely, benzoic acid and hydrogen sulfide being the main products,126 while, under the same conditions, the 3-toluene-p-sulfonyl derivative yields benzal-dehyde and toluene-p-sulfonylguanidine.125... 

Scheme 34 shows the synthesis of the bc portion (336), which possessed three of the nine asymmetric centers present in cobyric acid. Retrosynthesis determined that (336) could be obtained, via sulfide contraction, from the two intermediates (337) and (338). Ring c was synthesized from (+)-camphor quinone (not shown). Ring b (337) was obtained from 8-methyl-j8-acetylacrylic acid (339), the two adjacent chiral centers being generated in the required relative orientation by a Diels-Alder cycloaddition with butadiene in the presence of tin(IV) chloride. Fractional crystallization served to resolve the diastereomeric a-phenethylamine salts derived from them, eventually affording the compound (340). Oxidation with chromic acid cleaved the double bond in (340) and one of the newly generated... 

Reductive cleavage of O—O, O—N, O—S and S—N bonds is also possible. For example, the peroxide bond in the dioxazine (152) is cleaved by treatment with zinc in ethanolic potassium hydroxide, or by catalytic hydrogenolysis (64JOC291). Zinc in acid cleaves the S—N bond in (153) (68LA(715)223). Concomitant reduction of the sulfoxide also occurs, so that subsequent recyclization and aromatization with loss of ammonia leads to the ben-zothiazole (154). The O—S bond in (3) is reductively cleaved by sodium borohydride to give the alcohol (155) (77TL4245). 

Phenylselenol, diphenylphosphine and diphenylarsine cleave Pt—Me bonds, but N-bromosuccinimide and 2-nitrobenzenesulfenyl chloride oxidize the methyl platinum(II) compounds to methyl platinum(IV) complexes (equations 208 and 209).573 m-Chloroperbenzoic acid cleaves the Pt—benzyl bond in PtCl(CHDPh)(PPh3)2 with retention of configuration at carbon.574... 

Treatment with aqueous sulfuric acid cleaves the MOM protective group (which consists of an acetal structure) to give compound 48. 

Boron tnchlonde acting as a Lewis acid cleaves ben/ylic ether 37 selectively to 38.IJ The third reaction, like the transiormation of 4 to 5, leads to a rranv-P-alkoxyacrylate 7... 

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