Cyanohydrins rearrangement

Claisen rearrangement, 660 conjugate carbonyl addition reaction, 725-726 Curtius rearrangement, 935 cyanohydrin formation, 707 dichlorocarbene formation, 227 Dieckmann cyclization reaction, 892-893... 

Since the key thermal rearrangement was optimized, we turned our attention to earlier steps. The synthesis of amidoxime 7 was optimized from acetone cyanohydrin 4 (Scheme 6.6). The original Strecker reaction was carried out with ammonia... 

Two one-pot syntheses of highly substituted pyran-2-ones have been published. One involves the reaction between t-BuNC, dialkyl acetylenedicarboxylates and bromomalonates <99JCR368>. In the other, cyclobutenediones are treated with 0-silylated cyanohydrins to yield a 4-acylcyclobutenone by a 1,4-silyl migration and cyanide displacement which rearranges to the pyranone (Scheme 18) <99JOC2145>. 

The methyl ester has also been obtained by esterification of cyclopentanecarboxylic acid.8 The acid, in turn, has been prepared by the Favorskii rearrangement,6 7 9-11 by the reaction of cyclopentyl Grignard reagent with carbon dioxide,12 by the carbonylation of cyclopentyl alcohol with nickel carbonyl13 or with formic acid in the presence of sulfuric acid,14 and by the hydrogenation of cyclopentene-1-carboxylic acid prepared from ethyl cyclopentanone-2-carboxylate 15 or from cyclopentanone cyanohydrin.16... 

Mode of synthesis A. cyanohydrin, by way of 2-nmino-2-deoxy-aldonic acid B. scission of sugar derivative epoxide with ammonia C. interconversion of hexosamine series D. hemihydrogenation of a-amino nitrile466 E. rearrangement of ketosyl-amine F. Removal of last carbon atom of hexosamine G. Hydrazinolysis (with inversion) of 2-0-tosyl-pentose. 6 Physical constants taken from this reference. c Derivatives (only) isolated. 

Fig. 14.21. Ring expansion of cyclic ketones via the Tiffe-neau-Demjanov rearrangement. The first step consists of the additions of HCN or nitromethane, respectively, to form either the cyanohydrin or the /J-nitroalcohol, respectively. The vicinal amino alcohol A is formed in the next step by reduction with LiAlH4. TheTiffeneau-Demjanov rearrangement starts after diazota-tion with the dediazotation.

The oxidation of a 12-hydrazone (248) with lead tetra-acetate provided a novel route to rearranged steroids with the C-nor-D-homo structure (249), although another isomer was formed simultaneously. Dehydration of a C-12 cyanohydrin with thionyl chloride gave the 13a-cyano-c-nor-D-homo-compounds (250) and (251).209... 

The -matrices of Figs. 2 and 3 are representations for the molecules of the starting and end points of a chemical reaction, the formation of the cyanohydrin 1 of formaldehyde from its components 2 and 3. Taking the difference between these two matrices — from each element of the first matrix the corresponding element of the second matrix has to be subtracted — one obtains another matrix (see Fig. 5). This matrix is a representation of the reaction itself, and is therefore called a reaction matrix or / -matrix. Rearranging the matrix equation of Fig. 5 gives Fig. 6. 

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