The photolysis of fused cyclobutanotriazolines: Part 2 .n-2'-phthalimidoethyl and n-phenacyl 1,2,3-triazolines

Novel photochemistry of cyclobutanotriazolines with N-2’-phthalimido-ethyl and N-phenacyl substituents is reported. The main reaction path is fragmentation to an alkene and a triazole, while formation of aziridines by loss of dinitrogen is a minor reaction

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

Current status of synthesis of deprotected tridents by substituent variations of aza-ACE reaction

The N-bridged [n]polynorbornanes are a new class of N-bridged norbornanes that have become available using cycloaddition protocols developed by our group. [1] The basis for the synthesis is a dipolar cycloaddition reaction involving benzonorbornadienes as the dipolarophile and the 1,3-dipole formed by the ring-opening of a 5-azabicyclo[2.1.0]pentane. This reaction (the aza-ACE reaction [2]) requires that the aziridine be N-substituted thereby leading to the corresponding N-substituted polynorbornane (the trident). There are limitations on the type of substituent that can be introduced into the trident (eg the CBZ groups fail) and it has been necessary to find alternative groups that can be removed from the trident if the NH-bridged systems are to be accessed. This paper presents the results of our recent endeavours toward this goal of preparing NH-bridged tridents, especially those containing more than one NH-bridge

The trapping of 6,6-dimethylisobenzofulvene by its 1,3-dipolar precursor : a rare example of dipolar[6 4] cycloaddition

A new route to isobenzofuran and isobenzofulvene is reported that is proposed to involve the 14e electrocyclic fragmentation of a transient 1,3-dipolar intermediate formed by ring-opening of a fused aziridinocyclobutane. 6,6-Dimethylisobenzofulvene generated in this way reacts with its 1,3-dipole precursor to form a [10pi + 4pi] cycloadduct, the first of this type involving the participation of a 1,3-dipolar species

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

Tetrakis-(N-pyrrolyl)methane : structurally important member of the C(NR2)4 family

"It has been predicted that the polymorphic forms of carbon nitride are harder than diamond [1], and this auspicious speculation has prompted huge efforts to reliably prepare C3N4 [2]. Recently, there have been a number reports in surface science literature about the existence of carbon nitride phases as thin layers [3]. Carbon nitride is expected to have each nitrogen atom connected to three carbon atoms and each carbon atom connected to four nitrogen atoms. Although tertiary amines (NC3) are very common, compounds containing C(NR2)4 units are rare in organic chemistry, and very few examples have appeared in the literature (e.g., structures 1 [4], 2 [5], and 3 [6], Fig. 1). In this communication, we describe an interesting member of this class, namely tetrakis-(N-pyrrolyl)methane 4, comparable with the time-honored tetraphenyl analogue and prototype for a large family of tetrakis-N-[5-ring]heteroaryl methanes of which tetrakis-N-pyrazolyl methane 2 [5] appears to be the only other known member." --Introduction

Domino Diels-Alder reactions of N-methoxyethyl-7-oxa-norbornadiene-2,3- dicarboximide : an elusive, highly reactive dienophile

Flash vacuum pyrolysis (FVP) has been used to generate the novel 7-oxa-norbornadiene-2,3-dicarboxylic imide that in situ gave an unprecedented cycloaddition reaction cascade with the imidofuran, a side-product of FVP. Stereoselectivity of cycloadditions was studied with the aid of density functional calculations, which fully support observed exo/endo-selectivity

A cascade thermal isomerisation of cyclobutane di-(carbomethoxy) Δ2-1,2,3-triazolines with intramolecular 1,3-dipolar cycloreversion as the key step

Unprecedented thermal isomerisation of the strained ∆2-1,2,3-triazolines led to the formation of products possessing a novel 1,2,7-triaza-[3.3.0]octa-2-ene ring system incorporated in a norbornane framework. Experimental evidence and quantum chemical calculations have been used to support a postulated reaction mechanism involving as the first step, a rare example of intramolecular 1,3-dipolar cyclo-reversion. Subsequently, several steps involving 1,3-dipolar ring closure, hydrogen shifts and an intramolecular addition are postulated leading to the observed product of this deep-seated isomerisation. The influence of changing substituents on the product outcome of this novel reaction cascade was also studied

Cycloadditions of isobenzofuran to a constrained template bearing neighboring dienophiles

A high yielding synthesis of the pentacyclic diene - dione 1 has enabled investigation of its reactivity as a double dienophile in Diels - Alder [4+2] cycloadditions with isobenzofuran, leading to novel and highly symmetrical three-sided cavitands 3 and 4

Synthesis of bis-peptides attached on poly[n]norbornene molecular scaffolds with well-defined relative positions and distances

This article describes novel synthetic approaches to polynorbornene molecular scaffolds substituted with peptides at various, well-defined positions. A library of norbornene building blocks with attached peptides was prepared. Alkene cyclobutane epoxide (ACE) coupling method was used as a key step reaction for the connection of two norbornene building blocks into bis-peptide scaffolds. Photodimerization of cyclobutene diesters offers an alternative route to polynorbornene bis-peptides. Pyrrolo-peptides were used for preparation of peptide-substituted 7-aza norbornenes. Asymmetrical bis-peptide scaffolds were prepared by ACE coupling of peptide-norbornane epoxide with another norbornene-peptide block. Chemical elaboration of bridgehead dimethyl esters of ACE products or epoxide ACE reagents was also used for peptide attachment