Addition of formamides

The chain addition of formamide to alkenes is a closely related reaction. It results in the formation of primary amides. The reaction is carried out with irradiation in acetone. The photoexcited acetone initiates the chain reaction by abstracting hydrogen from formamide ... 

In a study of the formation of an inclusion complex between beta cyclodextrin and indole, the stability constant in aqueous solution was found, on the addition of formamide, to decrease, accompanied by a... 

The hybridization phase entails thermal denaturation of double-stranded DNA and incubation of the probe with the denatured DNA at a temperature 25°C below the melt temperature. Unless one is interested in partial homology, lower temperatures should be avoided. However, addition of formamide promotes the hybridization, thereby permitting the use of a lower temperature, if it should be required, to prevent structural modification. 

In the case of terminal olefins it was found that the major product of the reaction was the 1 1 adduct resulting from an anti-Markovnikov addition of formamide to the double bond. Products resulting from Mar-kovnikov-addition of formamide to olefins were also obtained, but in poor yields. In addition, smaller yields of higher telomers were also formed. In the case of nonterminal olefins mixtures of the two possible amides (1 1 adducts) were obtained. These amides resulted from addition... 

The photoamidation reaction has been applied to dienes of various types (61). These reactions need further investigation since the interaction of the excited sensitizer with the diene makes them complicated. The addition of formamide to 4-vinylcyclohexene as well as to m-1,5-cyclooctadiene led to 1 1 additions products (61). These reactions can be summarized as follows ... 

Since the addition of formamide to olefins is induced photochemically as well as by peroxides at elevated temperatures, it may be safe to assume that we deal here with a free radical reaction. Let us apply this assumption to interpret the results. A reasonable free radical derived from formamide would be a carbamoyl radical CONH2 which can be formed by loss of a hydrogen atom from formamide. Experimental data show that irradiation of formamide in the presence of acetone and in the absence of an olefin leads to the formation of considerable amounts of oxamide. 

The free radical chain-mechanism propose for the addition of formamide to isolated double bonds can be extended to include the present case as well. The carbamoyl radical involved adds to the double bond of norbomene from the less hindered exo side leading to the exo isomer exclusively,... 

As in cases already discussed, addition of acetone to norbomene also occurs (8% yield). This addition is also stereospecific leading to 2-exo-acetonylnorbomane, and thus following the steric route of the addition of formamide (58, 62). 

In this case the two ester groups seem to stabilize the radical more than one phenyl group (41). However, steric factors which may play an important role in the orientation of addition of the radicals to the double bond should not be ignored. This point, as well as some photochemical problems involving the sensitized addition of formamide to a,(3-unsatu-rated esters, need further experimental clarification. 

Elad, D. The Light-induced Addition of Formamide to Esters of Maleic, Fumaric, and Acetylenedicarboxylic Acids. Proc, chem. Soc. 1962, 225. 

RNA (is) is nonenzymatically hydrolysed in aqueous solutions at elevated temperatures (Tenhunen, 1989 Kaga et al., 1992). At 80°C, degradation occurs within 2 h, whereas at 60°C 55 RNA is partially destroyed within 6 h. Conditions generally used for DNA hybridization should therefore be modified, especially for quantitative studies of RNA. Since the length of hybridization affects the final results, this could explain why the degree of mismatch necessary to form a stable hybrid in RNA RNA hybridization is much less than that predicted by calculations. The addition of formamide allows hybridization to be carried out at lower temperatures without changing the stringency. 

This conclusion is supported by low-temperature 29Si NMR work of Boonstra and co-workers (21) on a two-step TEOS-ethanol sol-gel system. The results indicate that formamide acts as a base to reduce H+ concentration and the hydrolysis rate, but more importantly it also reduces the dimerization rate. In a two-step process, less than stoichiometric acidic water is added for hydrolysis, and condensation remains relatively slow. Dimerization is retarded, and so the number of free silanols available for condensation in the second step (addition of basic water) is enhanced. Thus, addition of formamide decreases the gel time by increasing the number of silanols for condensation. Gels with larger particle sizes and larger mean pore size are produced, and drying stresses are reduced. 

The reaction in Entry 12 is related and uses thioglycolate esters as a chain transfer agent. In this particular reaction involving an electron-rich alkene, the yield is only 8% in the absence of the thioglycolate. Entry 13 is another example of the addition of an acyl radical to relatively electrophilic alkene. Entry 14, involving the addition of formamide was done with acetone photosensitization. The 2-dioxolanyl radical involved in Entry 15 would be expected to be nucleophilic in character and higher yields were obtained with diethyl maleate than with typical terminal alkenes. The addition of 1,3-dioxolane to various enones has been done using benzophenone sensitization.The radicals in Entries 17 and 18 are electrophilic in character. Entries 19 and 20 are examples of thiol additions. 

Zee-Cheng and Cheng s (73JHC85 73JHC867) route to the benzo[c]phe-nanthridines utilized the formation of the N-formamide derivatives 41-43 from the corresponding tetralone intermediates 2939,40 by addition of formamide and formic acid under Leuckart conditions. The derivatives... 

The photosensitized addition of formamide to olefins is essentially an addition of H and CONH2 to the double bond (see e.g. 106) trans-annular participation of a second suitably located olefinic linkage has also been observed (106). Longifolene, however, gives only the unsaturated amides (159, 160), with no evidence of a 1,5-H shift product possibly because of fast abstraction by triplet acetone of a hydrogen a to the radical centre (107). 

Qosely related is the chain addition of formamide to olefins, a reaction that provides amides. The initiating radicals are generated photolytically. Excited-state acetone abstracts a hydrogen atom from formamide, and the addition is a chain process. 

In order to relate the effect of formamide on the gelation process and the subsequent structure of the xerogels, nitrogen sorption was performed. The results are provided in table II. The addition of formamide to acid catalyzed silica and silica/PVAc gels result in mesoporous, rather than microporous solids. Increasing the substitution of formamide for ethanol increases the BET surface area and pore volume. On the other hand, the addition of PVAc resulted in decrease of the BET surface area and pore volume for ual levels of formamide. 

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