David R. Dalton

Bromoformate formation in dimethylformamide

Dimethylformamide (DMF) is shown to react in a stereospecific, regioselective fashion with bromonium, or α-bromocarbonium ions, generated from a variety of olefins and N-bromosuccinimide (NBS) in the presence of water. The bromoformate is often accompanied by dibromide and bromohydrin; at least some of the latter arising from hydrolysis of the bromoformate. Although alkyl and aryl migration is not observed, rearrangement products derived from cationic intermediates through proton loss are found. The mechanism of formation of bromoformate is elucidated through the use of DMF-18O.

Thermal and photolytic decomposition of diarylmethylenetriphenylphosphazines and diaryldiazomethanes

Abstract Variously substituted diarylmethylenetriphenylphosphazines and diaryldiazomethanes have been subjected to thermal and photolytic decomposition conditions. The products obtained indicate the major pathway for fragmentation under both thermal and photolytic conditions to be one which serves to generate carbene, nitrogen and, in the case of the phosphazines, triphenylphosphine. The carbene produced from either diarylmethylenetriphenylphosphazine or diaryLdiazomethane undergoes reactions which appear to be dependent upon the medium in which it is generated and its inherent stability.

Syntheses of Morphine and Codeine (1992 - 2002): Templates for Exploration of Synthetic Tools

Abstract: Morphine ( 1 ) and its O-methylated analogue codeine ( 2 ), analgesic alkaloids of the opium poppy( Papaver Somniferium ), have been targets of organic chemists engaged in synthetic activities for at least half acentury. The “first” (Gates) and “most efficient” (Rice) syntheses of morphine ( 1 ) and codeine ( 2 ) are wellknown and have been reviewed and analyzed extensively numerous times. However, syntheses of the same twoalkaloids that have been reported since 1992 and which have been used as devices to advance the art of organicsynthesis are not as widely recognized and they have not been as thoroughly reviewed. Here they are analyzedin the spirit of the use of these two compounds as templates. Further, since both racemic and enantiospecificsyntheses are important and since all eight (8) approaches (since 1992) are sufficiently different so as towarrant more tha n superficial examination, they are all considered. ROOHOHHH NCH 3HOROHN HO CH 3 123456789101112131415 16 1, R = H

Neutral conversion af aldoximes into nitriles at low temperature

(E)-and (Z)-Aldoximes can be induced to lose water to yield nitriles at, or slightly above, room temperature in dichloromethane solution by treatment with 1,1′-dicarbonylbi-imidazole.

The Synthesis of Aporphine Alkaloids. III.1 Steric Effects in the Pschorr Cyclization

Abstract The decomposition of diazonium salts (e.g. 1 Z = N2 +X−) in the presence of a copper (and/or copper salt) catalyst in the solution in which they are generated is probably the most common variation of the Pschorr Cyclization Reaction2,3 as applied to the synthesis of Aporphine alkaloids (e.g. 2).

Nonsymmetric 9-Phenanthrylamines. An Improved Synthetic Procedure to a Useful Synthon

Abstract The ready availability1 of stilbene carboxylic acids and the ease of oxidative photochemical cyclization of these acids to phenanthrene-9-carboxylic acids 1, suggests this route as a straight-forward entry into natural products having unsymmetrical phenanthryl2,3 or phenanthryl - derived 4 structures. A major difficulty which has deterred the use of this approach in alkaloid synthesis is the difficulty of converting phenanthrene-9-carboxylic acids 1 into the corresponding 9-phenanthrylamines 4.2 Because of our need for a simple route to nonsymmetrical 9-phenanthrylamines 4 as key intermediates in the synthesis of the antileukemic lignan lactone steganangin4,5 and related compounds, we have developed improved synthetic procedures for conversion of phenanthrylic acids 1 to phenanthrylamines and derivatives 4 - 6. Results are shown in Table I.

Electron spin resonance studies on neutral aromatic hydrocarbon radicals : Substituent and isotope effects

Abstract The neutral, 13 C bearing, radicals diphenylmethyl and 9-fluorenyl have been generated in solution and the hyperfine coupling between 13 C and the free electron obtained. On the basis of this information, the nonplanarity assigned to these radicals is seen to lie not in the hybridization of C central , which is sp 2 , but rather in the “propellor” type disposition of the phenyl rings. Some substituted neutral diphenylmethyl radicals have also been examined and no simple correlation between the usual sigma σ substituent parameters and the hyperfine (a H ) splitting constants of the hydrogen at C central is apparent.

Surface Catalyzed Hydrochlorination of 1,3-Butadiene.

The rates of disappearance of gaseous hydrogen chloride (-d[HCl]/dt) and 1,3-butadiene and appearance of the gaseous products 3-chloro-l-butene and (E)- and (Z)-1-chloro-2-butene (+d[products]/dt) in Pyrex IR cells at 295 K and total initial pressures of about 450 torr are found to be proportional to the surface-to-volume ratio (S/V) of the reaction vessel.

Diastereoselective Diels–Alder reactions. The role of the catalyst

Abstract The Diels–Alder reaction between (R)-(−)-methyl (Z)-3-(4,5-dihydro-2-phenyl-4-oxazolyl)-2-propenoate (1) and cyclopentadiene in the presence of one equivalent of Et2AlCl gave stereochemical results opposite to those obtained with one equivalent of EtAlCl2. Energy minimizations of proposed complexes of these Lewis acids with the chiral dienophile at the RHF/3–21G level suggest that the aluminum is tetrahedrally complexed with Et2AlCl, but bound in a trigonal bipyramid with EtAlCl2. These complexes expose the diastereotopic faces of the dienophile to reaction with diene.

Stereochemistry of the diphenylmethyl radical

Abstract Interpretation of the electron spin resonance spectrum with regard to the stereo-chemistry of the diphenylmethyl radical was based on semiempirical relationships previously recorded by other workers. Computer spectral simulations and McLachlan theoretical spin-density calculations have aided in the structural analysis. In this report, influence of several geometric distortions on the hyperfine constants has been calculated by the INDO-MO method and supports previous contentions. Based on these considerations, it is concluded that the diphenylmethyl odd-alternate neutral free radical exists under the conditions of the experiments as a nonlinear, nonplanar species.