Daniel H. O'Brien

Sesquiterpenoid aldehyde quinones and derivatives in pigment glands of Gossypium

Abstract The resistance of Gossypium species to insects is enhanced by compounds in their lysigenous pigment glands. In cultivated cottons, glands in achlorophyllous plant parts contained predominately the terpenoid aldehyde gossypol in G. hirsutum , and gossypol and its methyl and dimethyl ethers in G. barbadense . Glands in young green tissues, however, contained hemigossypolone as the predominant terpenoid aldehyde in G. hirsutum , and a new quinone, hemigossypolone-7-methyl ether, in G. barbadense . As glands aged in green tissues, the sesquiterpenoid quinones were replaced by several C 25 -terpenoids formed by the Diels-Alder reaction of the quinones with myrcene or trans -β-ocimene. Two C 25 -terpenoids isolated from G. barbadense , but not G. hirsutum , were the methyl ethers of heliocides H 1 and H 4 and were designated heliocides B 1 and B 4 , respectively. A dark red pigment, gossyrubilone, from glands of young leaves of both species is the isopentylimine of hemigossypolone. Similar red imines, formed from sesquiterpenoid quinones and amino acids, resembled the red coloration of the envelope cells surrounding the gland sac. The terpenoid quinones of Gossypium had physical characteristics different from quinones in Bombax which apparently were incorrectly identified as being the same. A survey of the terpenoid quinones and their heliocide derivates in wild Gossypium species and related genera in the Gossypieae showed considerable diversity which may be used for establishing biochemical and phylogenetic relationships.

The Rearrangement of the trimethylsilyl group in (trimethylsilyl)pyrazoles

Abstract A new class of compounds, the N-(trimethylsilyl)pyrazoles, has been prepared. Four compounds with differing substituents on the pyrazole ring show non-equivalent 3,5-substituents in their NMR spectra. These compounds undergo temperature-dependent NMR spectral changes with the 3,5-substituents becoming equivalent at high temperatures. These spectral changes are due to the rearrangement of the trimethylsilyl group between ring nitrogens. The activation energies indicate that the rearrangement is sensitive to the size of the 3,5-substituents and to the electronic influences of all three ring substituents.

The reaction of (α-haloalkyl)silanes with Lewis acids☆

Abstract The kinetics for the reaction of three (α-haloalkyl0silanes with antimony pentafluoride in nitromethane have been studied using NMR to follow the reaction. For tertiary (α-haloalkyl)silanes, the reaction is stepwise with the intermediate formation of a charged species. The rearrangement–elimination reaction of this intermediate is sensitive to the Lewis acid used and to the inductive character and size of the alkyl groups attached to silicon. The kinetic and thermodynamic data are consistent with a mechanism involving nucleophilic attack at silicon before or during the rate determining alkyl migration or alkene elimination.

The reactions of diphenyllithioarsine and diphenylarsine with aldehydes

Abstract Diphenyllithioarsine reacts with aldehydes (RCHO, R  CH 2 CH 3 , CH(CH 3 ) 2 , and Ph) to form lithium salts of α-hydroxyalkylarsines. Protonation of the lithium salts gives α-hydroxyalkylarsines. Diphenylarsine reacts with aldehydes below room temperature in the absence of solvents to produce white solids. The reactions are rapid in the presence of acid catalysts. Proton and carbon-13 NMR, infrared and Raman spectra show that the products are diphenyl-(α-hydroxyalkyl)arsines, Ph 2 AsCHOHR. These compounds are thermally unstable. In organic solvents, equilibrium is established between the α-hydroxyalkylarsines and the aldehyde and diphenylarsine.

N-[(triorganylsilyl)alkyl]ethylenediamines

Abstract A series of N-organosilylalkyl-substituted ethylenediamines, R3Si(CH2)n-NHCH2CH2NH2 (R = CH3, C6H5 or 4-CH3C6H4 n = 1 or 3), were prepared by the reaction of haloalkylsilanes with ethylenediamine. The cleavage of a methyl group from silicon by concentrated sulfuric acid was used for the preparation of 1,3-bis-[N-(2-aminoethyl)aminomethyl]-1,1,3,3-tetramethyldisiloxane. The proton and carbon-13 NMR spectra of these compounds are reported.

Cleavage of alkylsilanes by strong acids

Abstract The stepwise cleavage of methyl groups from tetramethysilane and (chloromethyl)trimethylsilane has been studied in strong acid systems. The number of methyl groups cleaved can be controlled by varying the temperature and the acid strength. the progress of the reactions and the products formed can be directly observed by nuclear magnetic resonance. Relative rate studies under homogeneous conditions indicate that the key step in the mechanism is electrophilic attack of the acid at the methyl carbon.

Photochemical and thermal reactions of iron pentacarbonyl with dimethyldiacetylene (DMDA): spectral characterization of reaction complexes

Abstract A series of photochemical and thermal reactions has been carried out with iron pentacarbonyl and the conjugated alkadiyne dimethyldiacetylene (DMDA). One product (DMDA)Fe(CO) 6 , was prepared directly from starting materials in tetrahydrofuran under photochemical conditions. Previously analogs of this complex had been prepared only under thermal conditions from complex intermediates. An X-ray analysis has established the structure of this complex; 13 C NMR and other spectral data reported here are in agreement. Under thermal conditions in xylene, three isomeric forms of a tricarbonylferroleiron tricarbonyl (DMDA) 2 Fe 2 (CO) 6 complex were prepared. Separation and purification of two of these isomers was achieved; selected spectral data are reported. Infrared and mass spectra are also reported for the complex (DMDA) 2 Fe(CO) 4 resulting from the photochemical reaction of starting materials in cyclohexane.

Synthesis of 1-O-(2?,3?-dihydroxypropyl)5-deoxy-?-D-ribofuranosides with (CH3)2As, (CH3)2As?S or (CH3)3As+ groups as substituents at the 5-position

Eight arsenic-containing ribosides were prepared from dimethyl(1-O-methyl1-5-deoxy-2,3-O-isopropylidene-β-D-ribofuranos-5-yl)arsine and (2′S)-dimethyl[1-O-(2′,3′-isopropylidenedioxypropyl)-5-deoxy-2,3-O-isopropylidene-β-D-ribofuranos-5-yl]arsine. Reactions of the arsines with sulfur produced the compounds with a (CH3)2As &&dbond S group as substituent in the 5-position. Treatment of these dimethyl(ribosyl)arsine sulfides with trifluoroacetic acid water removed the isopropylidene groups and gave the unprotected derivatives as thick oils in 80% yield. The arsines and methyl iodide gave the protected trimethyl(ribosyl)arsonium iodides. These arsonium iodides were reacted with trifluoroacetic acid/water. Anomeric mixtures of the deprotected compounds were isolated. Deprotection of the dimethyl(ribosyl)arsines proceeded without anomerization. Reaction of the dimethyl[1-O-(2′,3′-dihydroxypropyl)-5-deoxy-β-D-ribofuranos-5-yl]arsine with methyl iodide produced the pure β-anomer of the arsonium iodide. The yields in these reactions were approximately 80%.

Cleavage of alkylsilanes by strong acids : III. The reactions of (halomethyl)trimethylsilanes with fluorosulfonic acid

Abstract The stepwise cleavage of alkyl groups from (bromomethyl)trimethylsilane and (iodomethyl)trimethylsilane by fluorosulfonic acid has been studied with proton magnetic resonance. Exclusive methyl cleavage is observed in the first reaction of both compounds. The reaction of (bromomethyl)dimethylsilyl fluorosulfonate occurs with cleavage of both methyl and bromomethyl from silicon. The reaction of (iodomethyl)dimethylfluorosilane occurs with exclusive cleavage of the iodomethyl group.

Cleavage of alkylsilanes by strong acids II. The formation of methanesulfonyl fluoride

Abstract The cleavage of methyl groups from trialkylsilyl fluorosulfonates by fluorosulfonic acid has been found to yield appreciable amounts of methanesulfonyl fluoride in addition to the formation of methane. Kinetic data show that this new mode of cleavage occurs after initial protonation of the silyl fluorosulfonate by the acid. A mechanism is proposed for methanesulfonyl fluoride formation in which nucleophilic attack by an acid molecule occurs at the silicon of the protonated silyl fluorosulfonate and is followed by rearrangement of a methyl group from silicon to sulfur.