Cyclopropyl Building Blocks for Organic Synthesis, 37. Synthesis and Diels—Alder Reactions of 2-Substituted 2-Cyclopropylideneacetates in Comparison with Allenecarboxylate and Ordinary Acrylates

Diels-Alder reaction of β-fluoro-β-nitrostyrenes with cyclic dienes

The Diels–Alder reaction of β-fluoro-β-nitrostyrenes with cyclic 1,3-dienes was investigated. A series of novel monofluorinated norbornenes was prepared in up to 97% yield. The reaction with 1,3-cyclohexadiene permits the preparation of monofluorinated bicyclo[2.2.2]oct-2-enes. The kinetic data of the reactions with 1,3-cyclopentadiene and 1,3-cyclohexadiene were used to calculate activation parameters. Furthermore, the synthetic utility of the cycloadducts obtained was demonstrated.

A Chiral Naphthyridine Diimine Ligand Enables Nickel-Catalyzed Asymmetric Alkylidenecyclopropanations

A novel class of chiral naphthyridine diimine ligands (NDI*) readily accessible from C₂ -symmetric 2,6-di-(1-arylethyl)anilines is described. The utility of these ligands, particularly one with fluorinated aryl side arms, is demonstrated by a reductive Ni-catalyzed enantioselective alkylidene transfer reaction from 1,1-dichloroalkenes to olefins. This transformation provides direct access to a broad range of synthetically valuable alkylidenecyclopropanes in high yields and enantioselectivities.

Synthesis of Methylenecyclopropane Analogues of Antiviral Nucleoside Phosphonates

Synthesis of methylenecyclopropane analogues of nucleoside phosphonates 6a, 6b, 7a and 7b is described. Cyclopropyl phosphonate 8 was transformed in four steps to methylenecyclopropane phosphonate 16. The latter intermediate was converted in seven steps to the key Z- and E-methylenecyclopropane alcohols 23 and 24 separated by chromatography. Selenoxide eliminations (15 --> 16 and 22 --> 23 + 24) were instrumental in the synthesis. The Z- and E-isomers 23 and 24 were transformed to bromides 25a and 25b which were used for alkylation of adenine and 2-amino-6-chloropurine to give intermediates 26a, 26b, 26c and 26d. Acid hydrolysis provided the adenine and guanine analogues 6a, 6b, 7a and 7b. Phosphonates 6b and 7b are potent inhibitors of replication of Epstein-Barr virus (EBV).