Cyclic adduct

Elemental sulfur undergoes nucleophilic attack by amines at low temperatures. Therefore the conjugate position of an enamine is sufficiently nucleophilic to attack elemental sulfur and yield thiolated intermediate 103. When 103 is treated when phenyl isothiocyanate, the cyclic adduct 104... 

To overcome this problem and obtain desired [P(aa)2(bb)] or [P(aa)(bb)(cc)] type products in high yields and to the exclusion of all others, it is necessary to consider a synthetic route that allows the sequential introduction of each of the three ligands in three different and orthogonal chemical steps. This is done by treating PX3 derivatives (X=halogens, NR2, ORf) with diols to form mono-cyclic adducts, which are in turn oxidized to bicyclic spirophosphoranes using... 

Baccolini et al. developed a novel method for the synthesis of 2-phenyl derivatives of 2//-[l,2,3 Idiazaphospholcs [17], which are otherwise difficult to obtain from the condensation of hydrazones and PC13. Fused benzothiadiphosphole 4 was used as a phosphorus furnishing reagent in its reaction with conjugated phenylazoalkenes 3 to obtain 2-phenyl-[l,2,3]diazaphospholes (6, R =Ph) via intermediacy of a spiro-cyclic adduct 5 (Scheme 2). 

The possible mechanisms of inhibition of flavin by (—)-deprenyl, as an irreversible acetylenic inhibitor, were studied by ab initio methods with the 6-31G basis set using simplified model compounds, 3-formyl-2-imino-l-hydroxypyrazine, and propargylamine. The formation of two energetically stable cyclic adducts, the 0,N adduct 286 and a C,N adduct, was shown <1999THA147>. 

Qualitative spot tests for aldehydes, in the presence of ketones, are generally only reliable for water-soluble compounds. This problem can be overcome by the use of 4-amino-3-hydrazino-5-mercapto-1,2,4-triazole (Purpald , Aldrich Chemical Company) in the presence of Aliquat (Scheme 5.27). Under aerial oxidation, the initially formed colourless cyclic adduct changes colour through red to purple. The colourless cyclic aminal can also be formed by ketones, but only the adducts derived from the aldehydes are oxidized to the purple bicyclic aromatic system [28]. Weakly electrophilic aldehydes, e.g., 4-methoxybenzaldehyde, reacts slowly, but will give the positive coloration upon gentle heating to ca. 70°C for one or two minutes. 

Now, dienes with shielded donble bonds can be involved in diene synthesis. The presence of donor gronps at the double bond normally prevents its involvement in conventional Diels-Alder condensations. These reactions do take place with the cation-radicals. Cyclic adducts are formed in high yields (80-90%) and under mild conditions. Polymerization, which usnally decreases the yield is inhibited completely within the framework of the cation-radical variant (Bellville et al. 1981). The stereoselectivity of the addition, which is usually typical for diene condensation, does not change in the cation-radical version and even increases. The positional selectivity also increases. The regiose-lectivity is enhanced, as well. Bauld et al. have discovered and explained these effects (Bellville and Banld 1982, Bellville et al. 1981, 1983, Banld and Pabon 1983, Pabon and Banld 1984). 

The interaction between orbitals of equal symmetry is an indispensable condition of the condensation under consideration. As seen from Scheme 7.22, the condensation becomes possible only when the diene and dienophile supplies four electrons and one electron, respectively. Bauld et al. denote such interaction as [4 -f 1]. If the diene and dienophile respectively supply three and two electrons (in the manner of [3 -l- 2] electrons), no cyclic adduct is formed. 

The central Co,=Cp double bond of an allenylidene backbone can also react with a variety of dipolar organic substrates to yield cyclic adducts. Most of the cychza-tion processes reported occur in a stepwise manner via an initial nucleophilic attack at the Coi atom and further rearrangement of the molecule involving a coupling with the Cp carbon. Representative examples are the reactions of the electron-poor ruthenium-allenylidene complex 46 with ethyl diazoacetate and 1,1-diethylpropar-gylamine to yield the five- and six-membered heterocyclic compounds 82 and 83, respectively (Scheme 29) [260, 284]. 

The type of O2 adduct depends on the donor structure. For example, tetraphenyl-oxirane forms an ozonide (78), " 1,4-bifunctional radical cations form dioxanes (79) conjugated dienes form cyclic adducts (80) and ergosteryl acetate (81) forms the 5a,8fl-peroxide (82) at —78... 

Finally, Fig. 17 shows the geometry of the cyclic adduct formed by azide with NP, together with the calculated decomposition paths, with different possible intermediates (see Eq. (22)). Although the cyclic structure has been predicted for related metallonitrosyl adducts (82), this was not the case for the reaction with NP, where a... 

Fig. 17. Possible decomposition paths of the cyclic adduct formed by reaction of [Fe(CN)eNO]2 with azide, (a) N2 release and stabilization of the N20-bound intermediates, (b) N20 release and stabilization of the N2-bound intermediate, (c) N40 release promoted by OH substitution. The cyclic species decomposes to give N20 and N2 in a reaction that is exothermic by 60 kcal mol-1. The structures correspond to single points on the potential hypersurface, calculated at the B3LYP/6-31G level. Relative energies are not drawn to scale. Arrows indicate changes in the molecule that lead to the next step.

Glycidaldehyde induces mutations in bacteriophage T4, bacteria, yeast and sex-linked recessive lethal mutations in Drosophila melanogaster, but not hprt locus mutations in mouse lymphoma L5178Y. DNA adducts can be found in vitro using calf thymus DNA and in vivo in skin cells of mice treated topically with glycidaldehyde. The main adduct, in this case, has been identified as a cyclic adduct of deoxyadenosine, namely, 3-p-D-deoxyribofuranosyl-7-(hydroxymethyl)-3/7-imidazo[2,l-z]purine-3 -monophosphate. The... 

Protection of primary amines. Primary amines form the cyclic adducts 2 ("Stabasc adducts ) on reaction with I and a base (triethylamine for amines with pK 10 II, -butyllithium for less basic amines). The adducts are stable to n- and. KT-BuLi (-25°), LDA, H 0, CH3OH, KF, and NaHCOj but unstable to HOAc, HC1, KOH, and NaBH. ... 

Side chain cleavage (Group c). In a third type of reaction the side chain of the Schiff base of Fig. 14-5 undergoes aldol cleavage. Conversely, a side chain can be added by (3 condensation. The best known enzyme of this group is serine hydroxymethyltransferase, which converts serine to glycine and formaldehyde.211-21313 The latter is not released in a free form but is transferred by the same enzyme specifically to tetrahydrofolic acid (Eq. 14-30), with which it forms a cyclic adduct. 

In addition reactions an excited, unsaturated molecule uses its weakened rr bond to form two new o bonds when these a bonds form a new ring in the molecule MN the reaction is one of cycloaddition . Thus alkenes can add photochemically to alcohols, as shown in Figure 4.51(a) to form a non-cyclic adduct or to other alkenes in cycloaddition processes Figure 4.51(b). 

Photo-crosslinking and the reverse process of photodissociation of pre-existing crosslinks relies on a cycloaddition reaction (and on the reverse dissociation of the cyclic adduct). For example, derivatives of vinyl cinnamic acid can form crosslinks which are dissociated by irradiation with short wavelength light (e.g. 254 nm produced by low-pressure mercury arcs). In this process the polymer chains become separated, and the polymer itself is then soluble in organic solvents. 

The cyclic peroxymetalation process (inner half-circle of Scheme 3) involves the peroxo species (70a) as the reactive intermediate. The cyclic adduct (72a) can result (a) from the reaction of an Rhin-peroxo complex with an alkene or (b) from the reaction of an Rh -ir-alkenic complex with 02. Indeed, both of these reactions (a) and (b) have been shown to occur. 

The first attempt to add diazomethane to a Schiff base was made by Meerwein,326 and the first successful addition was observed by Mustafa.327 Anils bearing nitro groups on the phenyl rings gave a cyclic adduct to which a 1,2,4-triazoline structure was assigned.327 A later reexamination of the reaction established the correct orientation of addition, and the products of the reaction of diazomethane with Schiff bases were assigned a A2-l,2,3-... 

Nakadaira and coworkers171 described the reaction of 6-trimethylsilylhex-l-ene with 1,2,4,5-tetracyanobenzene in which both the cyclic adduct 336 and the acyclic product 337 were formed (equation 32), and other workers further investigated the mechanistic details of this and related alkylations172. 

The cyclic adduct 109 is obtained from 105 and divinyl sulfoxide (equation 143)368,369. 

As the Diels-Alder cyclic adduct 33 has been recognized as the most accessible starting compound for the synthesis of racemic pseudo-sugars, a resolution of 33 has been attempted to prepare enantiomeric pseudo-sugars, starting from an optically active antipode of 33. It has been revealed that 33 was readily separated into the enantiomers by using optically active a-methylbenzylamines as resolution reagents. 

Styrene and substituted styrenes react with tetramesityldisilene 1, tetra-tert-butyl-disilene 21, and tetrakis(tert-butyldimethylsilyl)disilene 22 to afford the corresponding disilacyclobutane derivatives.127,134 Similarly, [2 + 2] additions occur between the disilenes with a C = C double bond in an aromatic ring135 and acrylonitrile.136 Bains et al. have found that the reaction of disilene 1 with trans-styrene- provides a 7 3 diastereomeric mixture of [2 + 2] adducts, 201 and 202 [Eq. (95)] the ratio is changed, when czs-styrene-Ji is used.137 The formation of the two diastereomeric cyclic adducts is taken as the evidence for a stepwise mechanism via a diradical or dipolar intermediate for the addition, similar to the [2 + 2] cycloaddition of phenylacetylene to disilene ( )-3, which gives a 1 1 mixture of stereoiso-meric products.116,137... 

The reaction of 1,2-dihydrophosphinine oxides 150A and 150B with tetra-cyanoethylene (TCNE) does not follow the Diels-Alder reaction, but rather follows the reaction of two moles of dihydrophosphinine (both of the two double bond isomers) with one mole TCNE to give a 2 1 cyclic adduct, via the 1 1 adduct, due to the ionic or radical nature of TCNE. The... 

This intramolecular reaction results in the formation of a cyclic system, and therefore it is called ring-closing metathesis (RCM). In this process a diene 36 is treated with a metal alkylidene 37. Two competing pathways are available via the intermediate metal alkylidene 38 A) RCM will occur to afford cyclic adducts 39 and B) intermolecular reaction can occur to form polymeric structures 40 (acyclic diene metathesis polymerization (ADMET)). The reaction is also complicated because of the possibility of ring-opening metathesis (ROM), the retro reaction of path A, and ring opening metathesis polymerization (ROMP) (path C).13... 

Two different 1 1 adducts were obtained from the reaction of 1,1-diphenylcy-clopropane with tetracyanoethylene. A cyclic adduct (52) was accompanied by an acyclic addition product (53). Both adducts are compatible with a 1,5-bifunctional... 

Under photochemical conditions several 1,4-dipoles reacted with alkenes, alkynes, phenyl isothiocyanate and carbon disulphide to afford, after iodobenzene expulsion, cyclic adducts in moderate to low yields. This drawback is offset by the fact that it is difficult to obtain some of these compounds through alternative methods. Table 10.6 are listed selected examples of cyclic compounds formed by this methodology. Formally, these reactions can be considered as 1,3-dipolar cycloadditions, in which the 1,3-dipole comes from the iodonium precursor after elimination of iodobenzene actually, they arise most probably through 6-membered intermediate iodanes. 

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