Addition reactions heterocycles

Addition nomenclature, 1, 37 Addition reactions heterocyclic compounds reviews, 1, 70 Additives... 

Addition reactions. Heterocyclic J enamino esters of the dihydrofurarie type... 

Studies on covalent hydration of N-heterocycles (67AG(E)919,76AHC(20)117) have revealed the diagnostic value of alkyl substituents in structural assignments due to their steric hindrance effects in addition reactions. C-Methyl substituents are therefore also considered as molecular probes to solve fine-structural problems in the pteridine field. The derivatives... 

Furan and thiophene undergo addition reactions with carbenes. Thus cyclopropane derivatives are obtained from these heterocycles on copper(I) bromide-catalyzed reaction with diazomethane and light-promoted reaction with diazoacetic acid ester (Scheme 41). The copper-catalyzed reaction of pyrrole with diazoacetic acid ester, however, gives a 2-substituted product (Scheme 42). 

Soon after the discovery of the addition reaction between diene-ophiles and dienes which now bears their names, Diels and Alder extended their investigations to include potential heterocyclic dienes. In 1929 the first compound investigated, furan, was observed to combine with maleic anhydride, like butadiene in a typical Diels-Alder reaction, across the 2,5-positions yielding a 1 1 molar adduct... 

The heterocyclic telluride 32 is susceptible to oxidation-addition reactions and readily adds halogen atoms under a treatment with halogens or sulfuryl chloride (93MI1). Compounds 34 were obtained in almost quantitative yields. 

Asymmetric syntheses of heterocycles by conjugate addition reactions 98EJO2051. 

Oxidative addition reactions of platinum(II) complexes with N-heterocyclic ligands 97CRV1735. 

Quinoxalines undergo facile addition reactions with nucleophilic reagents. The reaction of quinoxaline with allylmagnesium bromide gives, after hydrolysis of the initial adduct, 86% of 2,3-diallyl-l,2,3,4-tetrahydroquinoxaline. Quinoxaline is more reactive to this nucleophile than related aza-heterocyclic compounds, and the observed order of reactivity is pyridine < quinoline isoquinoline < phenan-thridine acridine < quinoxaline. ... 

Thiophene, a sulfur-containing heterocycle, undergoes typical aromatic substitution reactions rather than addition reactions. Why is thiophene aromatic ... 

Abstract The use of A-heterocyclic carbene (NHC) complexes as homogeneous catalysts in addition reactions across carbon-carbon double and triple bonds and carbon-heteroatom double bonds is described. The discussion is focused on the description of the catalytic systems, their current mechanistic understanding and occasionally the relevant organometallic chemistry. The reaction types covered include hydrogenation, transfer hydrogenation, hydrosilylation, hydroboration and diboration, hydroamination, hydrothiolation, hydration, hydroarylation, allylic substitution, addition, chloroesterification and chloroacylation. 

Entry 10 was used in conjunction with dihydroxylation in the enantiospecific synthesis of polyols. Entry 11 illustrates the use of SnCl2 with a protected polypropionate. Entries 12 and 13 result in the formation of lactones, after MgBr2-catalyzed additions to heterocyclic aldehyde having ester substituents. The stereochemistry of both of these reactions is consistent with approach to a chelate involving the aldehyde oxygen and oxazoline oxygen. 

Two types of addition to pyrimidine bases appear to exist. The first, the formation of pyrimidine photohydrates, has been the subject of a detailed review.251 Results suggest that two reactive species may be involved in the photohydration of 1,3-dimethyluracil.252 A recent example of this type of addition is to be found in 6-azacytosine (308) which forms a photohydration product (309) analogous to that found in cytosine.253 The second type of addition proceeds via radical intermediates and is illustrated by the addition of propan-2-ol to the trimethylcytosine 310 to give the alcohol 311 and the dihydro derivative 312.254 The same adduct is formed by a di-tert-butyl peroxide-initiated free radical reaction. Numerous other photoreactions involving the formation by hydrogen abstraction of hydroxyalkyl radicals and their subsequent addition to heterocycles have been reported. Systems studied include 3-aminopyrido[4,3-c]us-triazine,255 02,2 -anhydrouri-dine,256 and sym-triazolo[4,3-fe]pyridazine.257 The photoaddition of alcohols to purines is also a well-documented transformation. The stereospecific addition of methanol to the purine 313, for example, is an important step in the synthesis of coformycin.258 These reactions are frequently more... 

An independent synthesis of 120 was achieved by O-benzylation of 2,5-anhydro-D-gluconamide33 however, undesirable side-reactions made this alternative approach impractical. Compound 120 was subsequently transformed into a C-/3-D-arabinofuranosylated heterocycle by way of a 1,3-dipolar addition-reaction of the 1-diazo intermediate 122 to dimethyl acetylenedicarboxylate (see Section IV,2). 

Addition of Heterocyclic Compounds Stereocontrolled nucleophilic addition of heterocyclic compounds to chiral nitrones is of great synthetic importance in the synthesis of natural and biologically active compounds. In these reactions, the nitrone group serves as an amino group precursor and the heterocycle furnishes the formyl group (from thiazole) (192, 195, 214, 215, 579) or the carboxyl group (fromfuran) (194-196, 580-584) (Scheme 2.149). 

In addition to alkenes and alkynes, allenes have attracted considerable interest due to their unique reactivity and multireaction sites. Therefore, transition-metal-catalyzed nucleophilic addition reaction of amines and imines to allenes has been extensively studied to prepare biologically important amines and nitrogen-heterocycles.31,31d... 

Nitrogen-containing heterocyclic compounds, including 1,2,3,4-tetrahydroqui-noline, piperidine, pyrrolidine and indoline, are also popular hydrogen donors for the reduction of aldehydes, alkenes, and alkynes [75, 76]. With piperidine as hydrogen donor, the highly reactive 1-piperidene intermediate undergoes trimer-ization or, in the presence of amines, an addition reaction [77]. Pyridine was not observed as a reaction product. 

An intramolecular cyclization of a tetrazole-containing nucleoside 64 has been observed by Chu and co-workers <1997JOC7267> (cf. other properties of this compound in Table 3). These authors reported that the 3-OH group on the arabinofuranose ring participates in an addition reaction at position 7 of the tetrazolo[l,5-c]pyrimidine ring to form 65 which is a dihydro derivative of the parent heterocycle. The final structure elucidation has been carried out with the help of the tricyclic tandem mass spectrometry (MS/MS) fragment 66. 

Among chiral auxiliaries, l,3-oxazolidine-2-thiones (OZTs) have attracted important interest thanks to there various applications in different synthetic transformations. These simple structures, directly related to the well-documented Evans oxazolidinones, have been explored in asymmetric Diels-Alder reactions and asymmetric alkylations (7V-enoyl derivatives), but mainly in condensation of their 7V-acyl derivatives on aldehydes. Those have shown interesting characteristics in anti-selective aldol reactions or combined asymmetric addition. Normally, the use of chiral auxiliaries which can accomplish chirality transfer with a predictable stereochemistry on new generated stereogenic centers, are indispensable in asymmetric synthesis. The use of OZTs as chiral copula has proven efficient and especially useful for a large number of stereoselective reactions. In addition, OZT heterocycles are helpful synthons that can be specifically functionalized. 

The examples illustrated in the almost 100 schemes in this chapter demonstrate how versatile donor-substituted allenes can be in synthetic processes. The major applications concern addition reactions and cycloadditions to the allenic double bonds, which furnish products with valuable functional groups. Of particular interest are metalations - usually at C-l of the allene unit - followed by reactions with electrophiles that deliver compounds which can often be used for cyclization reactions. A variety of highly substituted and functionalized heterocycles arises from these flexible methods, which cannot be obtained by other reactions. Many of these transformations proceed with good regioselectivity and excellent stereoselection. 

Diastereoselective 1,4- and 1,6-addition reactions of lithium amides to chiral naph-thyloxazolines were used by Shimano and Meyers108-110 for the synthesis of novel amino acids. For example, treatment of (S )-2-(l-naphthyl)-4-t-butyloxazoline with lithi-ated l,4-dioxa-8-azaspiro[4.5]decane and iodomethane provided the diastereomerically pure 1,4-addition product with excellent yield cleavage of the heterocyclic rings then gave the desired /3-amino acid (>99% ee/ds equation 32)108,109. In contrast to this, most acyclic lithium amides reacted with these oxazolines under 1,6-addition the products were transformed smoothly to 5-amino acid derivatives (equation 33)110. 

N-Sulfinylaniline, the procedure for the preparation of which is described in Part A, is a versatile intermediate in the synthesis of heterocyclic compounds. Benzohydroxamoyl chloride, the method for the preparation of which is given in Part B, is the precursor of the highly reactive benzonitrile oxide, the diverse dipolar addition reactions of which have been thoroughly investigated. A wide array of heterocyclic compounds can be prepared starting with benzonitrile oxide. ... 

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