A Convenient Preparation of p-Methoxybenzyl Esters

Carboxylic acids are conveniently and efficiently protected as their p-methoxybenzyl esters under very mild conditions using the pre-formed reagent N,N-diisopropyl-O-(4-methoxybenzyl)isourea, and this method allows selective protection of carboxylic acids in the presence of other functionalities such as enolisable ketones and alcohol groups.     

Crystal Structure of N-Propargylcarbazole and N-(3-lodopropargyl)carbazole

An X-ray study of N-propargylcarbazole (I) and N-(3-iodopropargyl)carbazole (II) has been carried out. In the crystal II acetylenic groups form zigzag ladder-like infinite motives extended along the b axis. The motives are characterized by alternation of more close (and capable, in principle, of topochemical dimerization in crystal) and more distant pairs of acetylenic groups. A hypothetical possibility of topochemical polymerization in crystal II under uniaxial compression with formation of the ordered trans-polyacetylene is considered.     

Conformational polymorphs of 22‐cyano‐N‐methyl‐5‐phenylpent‐2‐en‐4‐ynamide

Although the two polymorphic modifications, (I) and (II), of the title compound, C₁₃H₁₀N₂O, crystallize in the same space group (P2₁/c), their asymmetric units have Z′ values of 1 and 2, respectively. These are conformational polymorphs, since the mol­ecules in phases (I) and (II) adopt different rotations of the phenyl ring with respect the central 2‐cyano­carboxy­amino­prop‐2‐enyl fragment. Calculations of crystal packing using Cerius² [Molecular Simulations (1999). 9685 Scranton Road, San Diego, CA 92121, USA] have shown that (I) is more stable than (II), by 1.3 kcal mol^?1 for the crystallographically determined structures and by 1.56 kcal mol^?1 for the optimized structures (1 kcal mol^?1 = 4.184 kJ mol^?1). This difference is mainly attributed to the different strengths of the hydrogen bonding in the two forms.     

Quadruply hydrogen bonded cytosine modules for supramolecular applications

In view of the range of properties required from supramolecular materials, there is clearly a need for new strong quadruple hydrogen bonded modules, which can be used in polymer or copolymer synthesis via the self- or hetero-association of complimentary units. A cytosine-based module has been prepared for supramolecular applications using a straightforward synthetic approach. The cytosine module was designed such that it does not undergo tautomeric changes observed with ureidopyrimidinones. The cytosine module was capable of forming quadruple hydrogen bonded assemblies both in solution and in the solid state, and the structure of the dimeric self-assembled unit was confirmed by single-crystal X-ray and solution NMR techniques. The dimerization constant was estimated to be greater than 9 x 106 M-1 in deuterated benzene. The capacity of the cytosine-based module to strongly hetero-associate with the ureidopyrimidinone module was demonstrated, and a supramolecular polymer of a bifunctional unit incorporating the cytosine module and PEG-based linker was described.     

Judicious application of allyl protecting groups for the synthesis of 2-morpholin-4-yl-4-oxo-4H-chromen-8-yl triflate, a key precursor of DNA-dependent protein kinase inhibitors

[Structure: see text] 2-morpholin-4-yl-4-oxo-4H-chromen-8-yl 2,2,2-trifluoromethanesulfonate is a key intermediate for the synthesis of the DNA-dependent protein kinase (DNA-PK) inhibitor 8-dibenzothiophen-4-yl-2-morpholin-4-yl-chromen-4-one (NU7441). Two improved methods for the synthesis of this triflate have been developed: (A) in 35% overall yield, through modification of the published route, and (B) in 15% overall yield, by a new route employing a Baker-Venkataraman rearrangement to enable generation of the chromenone scaffold. Both syntheses depend on the judicious use of allyl protecting groups.     

The orbital splitting patterns for the first and second-row elements

OPHF calculations for first and second-row elements have been performed and the results compared with the corresponding HF values. Systematic trends in the splitting of s and p-orbitals within, and between, rows are observed; in addition the splitting ratios decrease by at least an order of magnitude as one proceeds from a given shell to the next innermost shell.     

Facilitation of addition-elimination reactions in pyrimidines and purines using trifluoroacetic acid in trifluoroethanol

SNAr displacement reactions of 6-cyclohexylmethoxy-2-fluoropurine, 6-amino-2-butylsulfonyl-4-cyclohexylmethoxypyrimidine and 2-amino-6-chloropurine with substituted anilines (e.g. the weakly nucleophilic 4-aminobenzenesulfonamide) are dramaticallyaccelerated in the presence of trifluoroacetic acid and occur especially efficiently in 2,2,2-trifluoroethanol solvent.     

In situ FTIR studies on the electrochemical reduction of halogenated phenols

Electrochemical reduction of a variety of mono- and di-chloro- and bromo- phenols at a palladised titanium electrode afforded phenolate in all cases according to in situ FTIR studies, with the same intermediate species being observed in some cases.