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Reactions and reactivity of allyl and related carbamates.Mason, Paul Henry. January 1997 (has links)
Carbamate chemistry has flourished since the 1980's which saw the introduction of the
carbamoyl group by Hoppe and co-workers, prominent researchers in this area, as a
suitable moiety for the activation and stabilisation of alpha-heterocarbanions which are
important intermediates in synthetic organic chemistry. This functionality increases a-CH
acidity and stabilises the a-lithiocarbanion thus generated. The versatility of the
carbamate group has spawned investigations into the numerous possibilities that exist for
the functionalisation of the carbon alpha to the carbamate group. Some of these
possibilities were explored in the present work.
The direct formation of stable benzylic carbanions alpha to an oxygen atom is not a facile
process as such lithiated species are unstable and readily undergo a 1,2-Wittig
rearrangement. However, protection of the alcohol as the carbamate enabled
functionalisation of both benzylic sites with a variety of electrophiles.
Benzyl carbamates were found to react regioselectively with a,~-unsaturated electrophiles
to afford either the 1,2- or l,4-addition products. The regioselectivity could be controlled
by the presence or absence of a silyl moiety, either a trimethylsilyl or tertbutyldimethylsilyl
moiety, attached at the benzylic position, alpha to the carbamate.
The reaction of benzyl carbamates with 2-cyclohexen-1-one and 2-butenolide afforded the
1,2-addition adducts in moderate to good yields (25-66%). The isolation of the masked ahydroxy
ketone resulting from the opening of the lactone ring on reaction of 2-butenolide
with benzyl N,N-diisopropylcarbamate was surprising, as this electrophile is known to
behave as an excellent Michael acceptor. The introduction of a silyl moiety at the benzylic
position facilitated conjugate addition, yielding the corresponding Michael addition
products.
A novel cyclisation was observed on reaction of a-silyl benzyl carbamates with methyl
acrylate to give the a,y;y-trisubstituted butanolides (y-butyrolactones). The proposed
vii
mechanism of this reaction is discussed and illustrates the migrational ability of the
carbamate functionality.
Chiral induction in benzylic systems has only been investigated by a few authors. In the
present investigation two possible routes to chiral induction at the benzylic position were
investigated using either a (-)-sparteine-mediated transformation or chiral carbamates
derived from (L)-proline. (-)-Sparteine mediated transformations were solvent dependent
with the best enantiomeric excess of 28% being obtained. The results indicated that
racemisation at the benzylic position was faster than reaction with an electrophile. The
chiral carbamates were only slightly more successful yielding the a-substituted adducts
with diastereoselectiVities of the order of 20-50%. The diastereoselectivities were found to
be enhanced by the addition of HMPA which coordinated with the transition state blocking
one of the faces to attack by the electrophile.
The 1A-addition reaction with 2-butenolide was particulary useful as it allowed the
exploration of the synthesis of lignan derivatives from benzyl carbamates. Lignans are
secondary plant metabolites and exhibit.a wide range of biological activities. Applying the
methodology developed to the synthesis of lignans resulted in the preparation of an
arylnaphthalene lignan, in 79%, and the partial synthesis of racemic fargesin, a racemic
furofuran lignan.
This natural product synthesis highlighted the difficulty in removing the carbamate
functionality and re-introducing the alcohol moiety. Thus, hydrolytic cleavage of the
benzyl carbamates was investigated using a selection of mineral acids. Depending on the
reaction conditions, the products were found to be the corresponding benzyl alkanoates or
benzylhalides. The alkanoates are derived from nucleophilic displacement of the initially
formed benzyl halide A novel deprotection of a-silyl benzyl carbamates was also observed
in which the carbamoyl group was cleaved to afford the a-silyl alkanoates and chlorides
without the loss of the silicon moiety. / Thesis (Ph.D.)-University of Natal, Pietermaritzburg, 1997.
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Malathion specific resistance in a strain of the Rust Red Grain Beetle Cryptolestes ferrugineus (Stephens) (Coleoptera: Cucujidae)Spencer, Andrew George January 1995 (has links)
No description available.
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Effect of sublethal concentrations of azadirachtin on the development of Spodoptera littoralisCarvalho, Sueli Martinez de January 1996 (has links)
No description available.
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The functional basis of pyrethroid resistance in the malaria vector, Anopheles stephensiVatandoost, Hassan January 1996 (has links)
No description available.
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Insecticidal natural products from Sri Lankan plantsSamarasekera, Jayaneththi January 1997 (has links)
This thesis describes investigations of the insecticidal compounds of three Sri Lankan plants, <i>Pleurostylia opposita</i> (Wall) Alston (Celastraceae), <i>Aegle marmelos</i> Correa (Rutaceae) and <i>Excoecaria agallocha</i> Linn. (Euphorbiaceae). After establishing the insecticidal activity of the extracts of three plants, separation of compounds was achieved by bio-assay directed chromatography, and the compounds were characterised by NMR especially 2D experiments, mass, UV and IR spectroscopy. Three new macrocyclic sesquiterpene polyol ester alkaloids 1, 2 and 3 containing a novel 6,7 ring skeleton have been identified from the petroleum ether-ethyl acetate extract of the stem bark of <i>Pleurstylia opposita</i>. They are homologues of known macrocyclic sesquiterpene alkaloids which contains a 6,6 ring system based on the ß-dihydroagarofuran core. The extra methylene has been shown by NMR to be in the 8 position of the 6,7 ring. Observation of insecticidal activity in the <i>Pleurostylia</i> genus is novel. The previously reported 20-hydroxylupane-3- one has also been identified from the active extract and shown to be noninsecticidal. Two new insecticidal compounds 6 and 7 have been identified from the petroleum ether-ethyl acetate extract of the stem bark of <i>Aegle marmelos</i>. They are shown to be protolimonoids, and are senecioate ester analogues of the known isovalerate esters of C-21-ß and C-21-α glabretal which were also isolated. Compounds 8 and 9 were also found to be insecticidal against mustard beetles and houseflies. Separation and characterisation of epimeric mixtures were first achieved for the di p-nitrobenzoate derivative. Previously recorded epoxyaurapten, marmesin, marmin and lupeol have been isolated from the active extract of <i>Aegle marmelos</i> and shown to be noninsecticidal. Five compounds 24-28 have been isolated from the ethyl acetate extract of the stem bark of <i>Excoecaria agallocha</i>. They all have the previously reported daphnane diterpenoid orthoester skeleton, and differ only in the orthoester alkyl side chain. Two of them 24 and 27 are novel. Insecticidal activity has not been recorded previously for extracts of <i>Excoecaria</i> species, nor for the daphnane orthoesters.
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Effects of malathion on the vascular function in human skinBoutsiouki, Paraskevi January 2002 (has links)
No description available.
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107 |
Inheritance of chlordane resistance in the German cockroach, Blattella germanica /Jarvis, Floyd Eldridge, January 1955 (has links)
Thesis (Ph. D.)--Virginia Polytechnic Institute, 1955. / Vita. Abstract. Includes bibliographical references (leaves 51-52). Also available via the Internet.
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The absorption, translocation and accumulation of 32P labelled systematic insecticides in grape-vines, with particular reference to their use for the control of Phylloxera vitifoliae Fitch /Coombe, B. G. January 1956 (has links) (PDF)
Thesis (M. Ag. Sci.)--University of Adelaide, 1957. / Spine title: Systemic insecticides in grape vines. Typescript (copy). Includes bibliographical references (leaf . 82-84).
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An investigation of the roles of contact and systemic insecticides in the control of Sirex noct ilio F. /Horwood, D. W. January 1966 (has links) (PDF)
Thesis (M.Ag.Sc.)--University of Adelaide, Dept. of Entomology, 1966. / Typescript. Includes bibliographical references.
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An investigation of the effects [of] locust-control pesticides, Fenitrothion and Fipronil, on avian development using an 'in ovo' modelRuss, Melissa. January 2005 (has links)
Thesis (M.Sc.)--University of Wollongong, 2005. / Typescript. Includes bibliographical references: p.105-126.
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