Rearrangement reaction with formamides

The oximes of 4,5,6,7-tetrahydrobenzo[6]thiophen-4-one and -7-one undergo the Beckmann rearrangement to give 146 354 451 and 147 (R = H),362 respectively. Compound 147 (R=C1) may be prepared similarly and by treating 2-chloro-4,5,6,7-tetrahydrobenzo[ ]thio-phen-7-one with ammonia in the presence of PPA.356 The oxime of 4,5,6,7 -tetrahydrobenzo [6]thiophene- 4-one affords 4-aminobenzo [6]-thiophene in a modified Leuckart reaction.241,355 The same oxime may be converted into 4-amino-4,5,6,7-tetrahydrobenzo[ ]thiophene by reduction with aluminum amalgam in methanol.452 The parent ketone also affords 4-amino-4,5,6,7-tetrahydrobenzo[6]thiophene on reaction with formamide at 165°, followed by acidic hydrolysis of the resulting 4-formylamino compound.355... 

Acyl anions (RC(=0)M) are unstable, and quickly dimerize at temperatures >-100 °C (Section 5.4.7). These intermediates are best generated by reaction of organolithium compounds or cuprates with carbon monoxide at -110 °C and should be trapped immediately by an electrophile [344—347]. Metalated formic acid esters (R0C(=0)M) have been generated as intermediates by treatment of alcoholates with carbon monoxide, and can either be protonated to yield formic acid esters, or left to rearrange to carboxylates (R0C(=0)M —> RC02M) (Scheme 5.38) [348]. Related intermediates are presumably also formed by treatment of alcohols with formamide acetals (Scheme 5.38) [349]. More stable than acyl lithium compounds are acyl silanes or transition metal acyl complexes, which can also be used to perform nucleophilic acylations [350],... 

A fascinating e.s.r. investigation of the reactions in irradiated aqueous solutions of HCN and the CN anion has been effected. Use of the in situ radiolysis-e.s.r. method has shown that the primary radicals, H and OH (from the radiolysis of H2O), add to HCN in acid solutions to yield the H2C=N and HC(OH)=N radicals. The other intermediate, e q, also leads to H2C=N by addition followed by protonation. The reaction of OH andO with CN in alkaline solutions was found to produce a radical which is most probably CONHa (or CONH ). This radical is the same as that obtained from the reaction of OH with formamide. It is not clear as to whether the intermediate HC(OH)=N can rearrange to CONH2, but the reverse reaction is not found. Thus in experiments with HCONH2, the radical CONH2 is found under conditions where HCN yields HC(OH)=N. A theoretical... 

The Leuckart reaction (reductive amination of carbonyl compounds with formamide and formic acid) of 2-norbornanone and (lR)-(V-(3,3-dimethyl-2-oxo-l-norbornyl) acetamide furnishes the expected A-(2-norbornyl)formamides. (l/()-AI-(7,7-Dimethyl-2-0X0-l-norbornyl)acetamide, on the other hand, gives a product resulting from a Wagner-Meerwein rearrangement of the usual cationic intermediate followed by an unprecedented transamination, which affords an A,A-diacylammonium ion. Hydrolysis gives (15 )-A-(3,3-dimethyl-2-oxo-l-norbornyl)acetamide, which then undergoes the normal Leuckart reaction. 

A -Arylimincs (21a) can be oxidatively rearranged to formamides (21b) with sodium perborate.42 The reaction works best for secondary or aryl R groups. An oxaziridinc intermediate is proposed. Results with chiral secondary R groups indicate epimeriza-tion, suggested to occur via equilibration of (21a) with its enamine tautomer. 

A study of the photoaddition of formamide to olefins was undertaken with the aim of finding a new process for converting olefins to higher amides and possibly further to amines by reduction or by the use of the Hofmann rearrangement. Since hydrolysis of the amides to the corresponding carboxylic acids can be effected by standard procedures, this reaction provides a new process for carboxylation of olefins under mild conditions at room temperature. A similar reaction has been shown to take place in a thermal process, using peroxides as initiators (60). 

When heated with Raney nickel at 200°, substituted formamides rearrange with the elimination of ammonia to form a carbonyl compound (105). This is the reverse of the Leuckart-Wallach reaction. The reaction is postulated to take the following course ... 

White et a/, reported that ring-closing metathesis (RCM) of oxaziridine diene 37 afforded amide 38 and cycloalk-ene 39 in 7% and 36% yields, respectively <20010L413>. Under these conditions, oxaziridine-to-amide rearrangement is promoted. On reaction of oxaziridine 40 with KMn04 in acetone in the presence of 10% H2SO4, formamide acid 41 was isolated in 30% yield <2002T9431>. 

The addition of isocyanates to glycals, which has been studied thoroughly in connection with new methods of synthesizing lactams [256], usually affords a mixture of [2+2] and [4+2] cycloadducts. These primary reaction products are rather unstable and slowly rearrange to unsaturated amides, which can often be isolated directly from reaction mixtures [257,258]. In the case of simple dihydropyran derivatives 168, unsaturated A-substituted C-2 formamides 170 are the only isolable products (O Scheme 57) [259,260]. 

Reaction of ketones with hydrazoic acid proceeds similarly to the Beckmann rearrangement to give amides, while aldehydes yield nitriles and formamides under analogous reaction conditions (equations 4 and 5). 

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