Access to Fused Pyrroles from Cyclic 1,3-Dienyl Boronic Esters and Arylnitroso Compounds.

Complimentary to classical hydroboration and boron-Wittig reactions, a new, efficient access to cyclic 1,3-dienyl boronic esters has been developed via diene or triene metathesis. Subsequently, fused pyrroles were synthesized with a broad substrate scope from the reaction of cyclic 1,3-dienyl boronic esters with arylnitroso compounds using a one-pot hetero-Diels-Alder/ring contraction sequence.

Regioisomeric and Substituent Effects upon the Outcome of the Reaction of 1-Borodienes with Nitrosoarene Compounds.

A study of the reactivity of 1-borodienes with nitrosoarene compounds has been carried out showing an outcome that differs according to the hybridization state of the boron moiety. Using an sp(2) boron substituent, a one-pot hetero-Diels-Alder/ring contraction cascade occurred to afford N-arylpyrroles with low to good yields depending on the electronic properties of the substituents on the borodiene, whereas an sp(3) boron substituent led to the formation of stable boro-oxazines with high regioselectivity in most of the cases, in moderate to good yields. (1)H and (11)B NMR studies on two boro-oxazine regioisomers showed that selective deprotection can be performed. Formation of either the pyrrole or the furan derivative is pH- and regioisomer-structure-dependent. The results obtained, together with previous B3LYP calculations, support mechanistic proposals which suggest that pyrrole, or furan, formation proceeds via oxazine formation, followed by a boryl rearrangement and an intramolecular addition-elimination sequence.

Boron-substituted 1,3-dienes and heterodienes as key elements in multicomponent processes.

In the last few years, multicomponent reactions involving boron substituted 1,3-dienes have emerged as important tools in synthetic organic chemistry. The most significant recent results and developments obtained in this area are reported in this review.

A novel, efficient synthesis of N-aryl pyrroles via reaction of 1-boronodienes with arylnitroso compounds.

A one-pot hetero-Diels-Alder/ring contraction cascade is presented from the reaction of 1-boronodienes and arylnitroso derivatives to derive N-arylpyrroles in moderate to good yields (up to 82%).

Synthesis and cytostatic and antiviral activities of 2'-deoxy-2',2'-difluororibo- and 2'-deoxy-2'-fluororibonucleosides derived from 7-(Het)aryl-7-deazaadenines.

A series of sugar-modified derivatives of cytostatic 7-heteroaryl-7-deazaadenosines (2'-deoxy-2'-fluororibo- and 2'-deoxy-2',2'-difluororibonucleosides) bearing an aryl or heteroaryl group at position 7 was prepared and screened for biological activity. The difluororibonucleosides were prepared by non- stereoselective glycosidation of 6-chloro-7-deazapurine with benzoyl-protected 2-deoxy-2,2-difluoro-D-erythro-pentofuranosyl-1-mesylate, followed by amination and aqueous Suzuki cross-couplings with (het)arylboronic acids. The fluororibo derivatives were prepared by aqueous palladium-catalyzed cross-coupling reactions of the corresponding 7-iodo-7-deazaadenine 2'-deoxy-2'-fluororibonucleoside 20 with (het)arylboronic acids. The key intermediate 20 was prepared by a six-step sequence from the corresponding arabinonucleoside by selective protection of 3'- and 5'-hydroxy groups with acid-labile groups, followed by stereoselective SN 2 fluorination and deprotection. Some of the title nucleosides and 7-iodo-7-deazaadenine intermediates showed micromolar cytostatic or anti-HCV activity. The most active were 7-iodo and 7-ethynyl derivatives. The corresponding 2'-deoxy-2',2'-difluororibonucleoside 5'-O-triphosphates were found to be good substrates for bacterial DNA polymerases, but are inhibitors of human polymerase α.