Dalimil Dvořák

Transition-metal catalysis in michael addition of β-dicarbonyls : Tuning of the reaction conditions

Abstract (2,4- Pentanedionato) copper(I) and bis(2,4-pentanedionato)copper(II) together with boron trifluoride etherate catalyze Michael addition of β-dicarbonyls to cyclohexenone, cyclopentenone, 2-methylcyclopentenone, and 3-thienylidenemalonaldehyde.

COUPLING OF 6-CHLOROPURINES WITH ORGANOCUPRATES DERIVED FROM GRIGNARD REAGENTS : A CONVENIENT ROUTE TO SEC AND TERT 6-ALKYLPURINES

Abstract Purine derivatives bearing a secondary or tertiary alkyl group at the 6-position can be conveniently prepared by CuI mediated reaction of secondary or tertiary Grignard reagents with 9-substituted 6-chloropurines under very mild conditions.

Cycloaddition reactions of arylmethylenemalonaldehydes: an approach to 4-aryl-3,4-dihydro-2h-pyran-5-carboxaldehydes

Abstract The reaction of arylmethylenemalonaldehydes I with various types of olefins afforded a series of 4-aryl-3,4-dihydro-2H-pyran-5-carboxaldehydes III.

Selective Synthesis of 7-Substituted Purines via 7,8-Dihydropurines

A simple and efficient protocol for the preparation of 7-substituted purines is described. 6- and 2,6-Dihalopurines were N(9)-tritylated and then transformed to 7,8-dihydropurines by DIBAL-H. Subsequent N(7)-alkylation followed by N(9)-trityl deprotection with trifluoroacetic acid was accompanied by spontaneous reoxidation, which led to the 7-substituted purines at 55-88% overall isolated yields.

Arylmethylenemalonaldehydes and their heterocyclic analogues: A novel group of organic lewis acids

Abstract The first general synthesis of arylmethylenemalonaldehydes and their heterocyclic analogues has been developed; some physico-chemical properties and reactions of these compounds are briefly mentioned.

Covalent analogues of DNA base-pairs and triplets. Part 3: Synthesis of 1,4- and 1,3-bis(purin-6-yl)benzenes and 1-(1,3-dimethyluracil-5-yl)-3 or 4-(purin-9-yl)benzenes ☆

Abstract The Stille cross-coupling reactions of 1,4- and 1,3-bis(trialkylstannyl)benzenes 2 or 3 with 9-benzyl-6-chloropurine ( 1 ) led either to mono-coupled 4- or 3-[(tributylstannyl)phenyl]benzenes 5a and 5b or to bis(9-benzylpurin-6-yl)benzenes ( 4a or 4b ) depending on the ratio of the starting compounds, nature of the stannane and conditions. Analogous reaction of 1 with benzene-1,4-diboronic acid gave selectively 4a in good yield. The reaction of stannanes 5 with 1,3-dimethyl-5-iodouracil gave 1-(9-benzylpurin-6-yl)-4- or -3-(1,3-dimethyluracil-5-yl)benzenes ( 10a and 10b ) in low yields. Compounds 4 and 10 are novel types of covalently linked analogues of nucleobase-pairs.

Fischer chromium carbene complexes as nucleophiles in palladium-catalyzed allylic substitution reactions

The Pd-catalyzed reaction of carbanions derived from chromium aminocarbene complexes with allylic acetates and carbonates smoothly affords the corresponding allyl-substituted aminocarbenes. On the contrary, the same reaction of the anion derived from pentacarbonyl[(methoxy)methylcarbene]chromium(0) with cinnamyl acetate affords 5-methoxy-1-phenylhexa-1,5-diene, the product of 1-methoxyethen-1-yl group transfer.

Palladium-catalysed Claisen rearrangement of 6-allyloxypurines

Abstract6-Allyloxypurines readily undergo palladium-catalysed Claisen rearrangement under mild conditions affording N1-substituted hypoxanthines. In contrast with the previously reported protocol, the Claisen rearrangement can be performed using Pd(PPh3)4 or Pd(dba)2/dppf in dry THF at 60°C. The reaction can accommodate variously substituted allyl fragments to position N1 of the hypoxanthine skeleton with high yields. Retention of the double bond configuration during rearrangement was observed.

Regioselective and efficient synthesis of N 7-substituted adenines, guanines, and 6-mercaptopurines

A simple and efficient protocol for the preparation of N7-substituted adenines, guanines, and 6-mercaptopurines is described. The key step is the regioselective preparation of 7-substituted 6-chloropurines which are building blocks for the divergent synthesis of adenines, guanines, and 6-mercaptopurines by known procedures.Graphical abstract