Pyrimidine syntheses from N-Acyl-Acrylamides

The pyrimidine nucleus was first formulated as a cyclic structure by Pinner as early as 1884

π-Bond screening in benzonorbornadienes : the role of 7-Substituents in governing the facial selectivity for the Diels-Alder reaction of Benzonorbornadienes with 3,6-Di(2-pyridyl)-s-Tetrazine

Benzonorbornadiene 21, 7-spirocyclopropylbenzonorbornadiene 23, 7,7- dimethylbenzonorbornadiene 25, and 7-spirocyclopentylbenzonorbornadiene 27 have been reacted with 3,6-di(2-pyridyl)-s-tetrazine (rate: 21>23>25=27) to form symmetrical 4,5- dihydropyridazines which are stable towards fragmentation but rearrange with varying facility to their 1,4 isomers. The facial selectivity of attack on the π-bond changes from exo-attack for 21 and 23 to endo-attack for 25 and 27. The 7-spirocyclopropyl benzonorbornadiene 23 typically forms a mixture of dihydropyridazines with exo-stereochemistry, which undergo further stereochemical isomerisation to an exo-fused product upon acetylation (acetyl chloride in hot pyridine). Oxidation with DDQ of the dihydropyridazines individually or as mixtures gives the corresponding fused 3,6-di(2-pyridyl) pyridazines

The synthesis of O-bridged laticyclic polynorbornadienes

The synthesis of the parent oxabridged laticyclic diene, COC-[3]isopolynorbornadiene 5 and the bis(oxabridged) laticyclic diene, CO2C-[4]isopolynorbornadiene 7 have each been achieved in two steps from known starting materials; the hexachloro-derivatives of 5 and 7 are also reported

Sulfur-bridged molecular racks : O,S-sesquinorbornadienes, CNS-[3] and CNOS [4]polynorbornanes

Thiophene has been reacted under high-pressure (10 kbar) and temperature (1000C) with Nmethylmaleimide and N-phenylmaleimide to produce Diels-Alder exo- and endo-adducts in modest yields (25-36%). Reaction of 7-oxanorbornadiene-2,3-dicarboxylic anhydride 6, a highly reactive dienophile, with thiophene occurred under high-pressure (10 kbar) at 100oC to yield stereoisomeric 1:1-adducts by site selective attack at the maleic anhydride type of π-bond. This approach afforded the first examples of syn- and anti- heterobridged sesquinorbornadiene anhydrides 8 and 9 containing a sulfur bridge. Similar reaction of isobenzothiophene with 6 was even more facile as reaction occurred at room temperature and atmospheric pressure to yield benzo-analogues 12 and 13. Thermal fragmentation involving loss of furan and sulfur occurred from both classes of adducts under FVP (370 0C, 0.005 mbar) to produce phthalic anhydride or naphthalene-2,3-dicarboxylic anhydride respectively. The putative 7-thianorbornadiene intermediates 20 and 22, generated by loss of furan, were not detected. Reaction of exo-N-methyl 7-thianorbornene-5,6-dicarboxylic imide 4a with the ester-activated cyclobutenoaziridine 16 provided access to CNS-[3]polynorbornane 18, while similar addition of the exo,endo-isomer of O,S-benzosesquinorbornadiene 13 to 16 afforded the CNOS-[4] olynorbornane 19. These are the first S-bridged [n]polynorbornanes to be reported. Molecular modelling (AM1) has shown that Sn-[n]polynorbornadienes have a curved topology greater than On- n]polynorbornadienes but less than Nn-[n]polynorbornadienes

Pyramidalized olefins : a DFT study of the homosesquinorbornene and sesquibicyclo[2.2.2]octene nuclei

Density functional theory (B3LYPl6-31G*) was used to study a series of homosesquinorbornenes and sesquibicyclo[2.2.2loctenes. The compounds in which the two faces of the double bond are different are predicted to have a pyramidal double bond with butterfly bendings (v) ranging from 1.8 to 17.9". The degree of pyramidalization of these central double bonds is greater in the homosesquinorbornenes than in the sesquibicyclo[2.2.2loctenes

Position-addressable nano-scaffolds. II. The introduction of one, two, or three addressable succinimide linkage points onto the under-surface of 'southern' cavity bis-porphyins

Cavity bis-porphyins containing up to three addressable succinimide rings on the underface are reported for the first time. This is achieved by site-selective addition of o-chloranil to the 7-oxanorbornene TT-bond of O-bridged sesquinorbornadienosuccinimide (1a) to form a scaffold a-dione, followed by condensation with porphyrindiamine (12) to produce a porphyrin-containing norbornene BLACK (13) incorporated a succinimide ring fused to the underside. Dual 1,3-dipolar coupling of (13) with alicyclic bis-epoxides (15) formed the cavity bis-porphyrins (16) containing two succinimide rings while similar 1,3-dipolar coupling with succinimide-containing bis-epoxide (17) gave the extended cavity bis-porphyrin (18) having three succinimide rings within the cavity section a similar cycloaddition/condensation strategy provides the shortest route to cavity bis-porphyrins containina a single succinimide ring yet reported

Preparation of the first isobenzofuran containing two ring nitrogens : a new diels-alder diene for the synthesis of molecular scaffolds containing one or more end-fused 3,6-di(2-pyridyl)pyridazine ligands

Preparation of a stable, crystalline isobenzofuran containing two ring-nitrogen atoms, 4,7-di(2-pyridyl)-5,6-diazaisobenzofuran (diaza-IBF) (12), is reported here for the first time. Diaza-IBF was prepared using the s-tetrazine-induced fragmentation of 1,4-di(2pyridyl)-5,8-epoxy-5,8-dihydrophthalazine (9), for which a synthesis is provided. Diaza-IBF was also prepared by flash vacuum pyrolysis (FVP) of the isomeric N-methyl-1,4-di(2-pyridyl)-5,8-epoxy-5,6,7,8-tetrahydrophthalazine-6,7-dicarboximides (18) and (19), formed in three steps from furan, N-methyl maleimide, and 3,6-di(2-pyridyl)-s-tetrazine. Diaza-IBF was employed in cycloaddition protocols with alkenes to form scaffold mono- or bis-3,6-di-(2pryidyl)-pyridazine ligands having novel molecular architectures

Bisporphyrin cavities : from guest complexation to molecular capsule formation

Bisporphyrin cavities : from guest complexation to molecular capsule formatio