Synthesis of fused purinoquinazolines. Three new heterocyclic ring systems

The Ullmann reaction of 8-aminotheophylline or 8-aminocaffeine with 2-chlorobenzoic acid and of 8-bromotheophylline with ethyl-2-aminobenzoate afforded derivatives of three new heterocyclic systems: purino[7,8-α]quinazoline-5,9,11(6H,8H,10H)-trione, purino[8,9-b]quinazoline-2,4,11(1H,3H,5H)-trione and purino[8,7-b]quinazoline-2,4,6(1H,3H,11H)-trione, respectively.     

A new method for the synthesis of 3-hydroxymethylbenzofuran

A new one-step synthesis of 3-hydroxymethylbenzofuran, based on intramolecular cyclization of 2- （methoxymethyl）-2-（2＇-methoxymethyl-4＇-methylphenyl）-butanone I under diluted hydrochloric acid in THF, was developed. The mechanism for this process was investigated via chemical equilibrium shift of tautomer in acidic conditions. The applicability of this new method was studied further in this paper.     

A highly efficient iterative approach to fused ether ring systems

An iterative synthesis of fused ether ring systems has been developed. This strategy couples a cyclic enol ether oxidation and carbon-carbon bond forming reaction in one flask with an acid catalyzed cyclic acetal formation and alkoxide elimination in another flask. The result is a general and highly efficient two flask synthesis of fused ethers as are present in a wide variety of bioactive natural products.     

Novel heterocycles. 3. Synthesis of fused 1,3,2-benzodiazaphosphorin ring systems

Novel fused tricyclic phosphorus heterocycles 9 and 11 and the tetracycle 15 were synthesized by cyclization of 1-haloalkyl (or 3-haloalkyl)-2,3-dihydro-1,3,2-benzodiazaphosphorin-4(1H)one 2-oxides with sodium hydride. Some spectral data of the products are also discussed.     

The electrochemical reduction of some fused ring systems

The electrochemical reduction of some fused ring systems containing four carbonyl moieties has been studied in alcoholic aqueous media. A mechanism has been proposed and clarified in which one carbonyl is reduced to a methylene group via an uptake of four electrons.     

Reaction of phenolic mannich bases with enamines. General synthesis of pyran-containing fused ring systems

The reaction of o-phenolic Mannich bases with enamines yields cyclic O,N-acetals having a 2-aminodihydropyran or a spiropyranopiperidine structure in common. The 2-aminodihydro-pyrans are easily converted to 2-hydroxydihydropyrans and to pyrans. The preparation of a large variety of pyran-containing fused ring systems is reported.     

New aromatic systems having a fused thiazolium ring

The method developed for the synthesis of thiazolo[3,2-a]pyridinium salts has been extended to the first synthesis of simple thiazolo[3,2-a]pyrimidinium, thiazolo[3,2-a]-pyrazinium and thiazolo[2, 3-b]benzo[d]thiazolium salts. No method could be found for the cyclization of 4′-bromo-2-(2-benzoxazolylthio)acetophenone to the thiazolo[2,3-b]-benzoxazolium system.     

A new and efficient method for the synthesis of isoquinoline-3-carboxylate

An isoquinoline-3-carboxylate compound 3 was obtained with a moderate yield of 40% when N-acetyl-（3′-hydroxy-4′- methoxy-5′-methyl）phenylalanine methyl ester 1 was refluxed in HMTA/TFA. However, the anticipated product N-acetyl-（3′- hydroxy-4′-methoxy-5′-methyl-6′-formyl）phenylalanine methyl ester 2 could not be found. The possible mechanism was discussed in this article.     

A new method for the synthesis of CF3-containing aminovinyl ketones

A new method for the synthesis of aminovinyl trifluoromethyl ketones was developed. The method is based on the reactions of 4-sulfonyl-1,1,1-trifluorobut-3-ene-2,2-diols with various alkyl-, aryl-, dialkyl-, and alkylarylamines. The stereochemistry of the compounds obtained was studied.     

A new facile method for the synthesis of 3-imidazolylpropionic acid N-oxides

Chemistry of Heterocyclic Compounds - A facile and efficient method for the preparation of 3-imidazolylpropionic acid N-oxides has been developed. It involves condensation of 2-unsubstituted...     

A new method for annulation of the α-pyrone ring

New derivatives of coumarin, containing annulated α-pyrone rings, were obtained by reaction of the borate complexes of three isomeric acyl(hydroxy)coumarins with acid anhydrides. It was shown that the borate complex of 3-acetyl-4-hydroxy-2-pyrone also condenses with acetic anhydride to form a derivative containing a new annulated α-pyrone ring. __________ Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 4, pp. 513–517, April, 2007.     

A new method for the synthesis of dichlorophosphines

A new method for the synthesis of alkyldichlorophosphines by chlorination of alkylphosphines with phosphorus pentachloride under mild conditions is described.     

A new approach to construct a fused 2-ylidene chromene ring: highly regioselective synthesis of novel chromeno quinoxalines

Regioselective construction of a fused 2-ylidene chromene ring was achieved for the first time by using AlCl(3)-induced C-C bond formation followed by Pd/C-Cu mediate coupling-cyclization strategy. A number of chromeno[4,3-b]quinoxaline derivatives were prepared by using this strategy. Single crystal X-ray diffraction study of a representative compound e.g. 6-(2,2-dimethylpropylidene)-4-methyl-6H-chromeno[4,3-b]quinoxalin-3-ol confirmed the presence of an exocyclic C-C double bond with Z-geometry. The crystal structure analysis and hydrogen bonding patterns of the same compound along with its structure elaboration via propargylation followed by Sonogashira coupling of the resulting terminal alkyne is presented. A probable mechanism for the formation of 2-ylidene chromene ring is discussed. Some of the compounds synthesized showed anticancer properties when tested in vitro.     

A new approach to fused furan ring systems and benzofurans: Intramolecular cyclization reactions of unsaturated acyloxy sulfone derivatives

Unsaturated acyloxy sulfones 3 undergo intramolecular cyclization upon deprotonation with LHMDS in THF. Dehydration and double bond isomerization of the products upon exposure to acid, gave the fused ring furans, 4, in good yields. This strategy could be readily adapted to prepare substituted benzofurans 12 from the cyclization reactions of acyloxy sulfones 11 prepared from phenols. Finally, this approach could be successfully modified to access dihydropyrans and benzopyrans.     

A new stereocontrolled approach to fused polycyclic compounds containing a diketopiperazine ring

Representative (1S)- and (4S)-alkyl-1,4-dihydropyrazino[2,1-b]quinazoline-3,6-dione lactim ethers were regio- and diastereoselectively alkylated after metallation to give the corresponding 1,4-trans-isomers with retention of the stereocentres. The results were compared with the previously studied lactams. The (1R,4S)-dialkyl derivatives obtained by C(1)-alkyation with bifunctional reagents were lately cyclized to complex polycyclic compounds through a second N(2)-alkylation promoted by sodium iodide.