It is better to travel hopefully ... Classics in total synthesis. Targets, strategies, methods by KC Nicolaou and EJ Sorensen, VCH Publishers Inc., 1996, 798 pages. 49.95softcover(ISBN3−527−29231−4);49.95 softcover (ISBN 3-527-29231-4); 80.00 hardcover (ISBN 3-527-29284-5)

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Camptothecin Analogs and Methods of Preparation Thereof

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Camptothecin Analogs and Methods of Preparation Thereof

To read this abstract, please download this patent

Camptothecin Intermediates and Prodrugs and Methods of Preparation Thereof

The present invention relates to novel intermediates and prodrugs of camptothecin and related analogs

EPR and preparative studies of 5-endo cyclizations of radicals derived from alkenyl NHC-boranes bearing tert-butyl ester substituents

J.C.W. thanks EaStCHEM for financial support, and D.P.C. thanks the US National Science Foundation. Computational support was provided through the EaStCHEM Research Computing Facility.Radical H atom abstraction from a set of N-heterocyclic carbene (NHC) complexes of alkenylboranes bearing two tert-butyl ester substituents was studied by EPR spectroscopy. The initial boraallyl radical intermediates rapidly ring closed onto the O atoms of their distal ester groups in 5-endo mode to yield 1,2-oxaborole radicals. Unexpectedly, two structural varieties of these radicals were identified from their EPR spectra. These proved to be two stable rotamers, in which the carbonyl group of the tert-butyl ester was oriented toward and away from the NHC ring. These rotamers were akin to the s-trans and s-cis rotamers of α,β-unsaturated carbonyl compounds. Their stability was attributed to the quasi-allylic interaction of their unpaired electrons with the carbonyl units of their adjacent ester groups. EPR spectroscopic evidence for two rotamers of the analogous methyl ester containing NHC-oxaborole radicals was also obtained. An improved synthetic procedure for preparing rare NHC-boralactones was developed involving treatment of the alkenyl NHC-boranes with AIBN and tert-dodecanethiol.PostprintPeer reviewe

Highly Lipophilic Camptothecin Intermediates and Prodrugs and Methods of Preparation Thereof

The present invention relates to novel, highly lipophilic silatecan intermediates and prodrugs of DB-67 and other silatecans

EPR studies on the addition of ligated boryl radicals to carbonyl compounds

J.C.W. thanks EaStCHEM for financial support and D.P.C. thanks the US National Science Foundation. Computational support was provided through the EaStCHEM Research Computing Facility.The boron-centered radicals derived from alkenyl N-heterocyclic carbene (NHC)-boranes bearing ester substituents were recently found to ring close in 5-endo mode by addition to the oxygen atoms of the ester substituents. The inference from this was that NHC-boryl radicals might add intermolecularly to carbonyl-containing substrates. Several different NHC-boryl radicals were generated by H-atom abstraction from NHC-ligated trihydroborates. Electron paramagnetic resonance (EPR) spectroscopy proved that these did indeed add to the oxygen atoms of diaryl ketones with production of the corresponding bora-ketyl radicals. The same unusual regioselectivity of addition was observed with monoaryl ketones, but no bora-ketyls were observed with dialkyl ketones. Similarly, no bora-ketyl adduct radicals were observed with esters, even esters of benzoic acid. EPR spectroscopic evidence suggested that NHC-boryl radicals were also added to the O-atoms of aromatic aldehydes. Amine-boryl and phosphine-boryl radicals were also observed to add to the O-atom of benzophenone with production of the corresponding ketyl radicals.PostprintPeer reviewe

Constitutional Convention

Billings Gazette special issue about the Montana Constitutional Convention and government information articles pertaining to the subject. Included is a list of 1972 delegates.https://digitalcommons.mtech.edu/crucible_materials/1007/thumbnail.jp

Generation and structure of unique boriranyl radicals

J.C.W. thanks EaStCHEM for financial support. T.R.M. and D.P.C. thank the US National Science Foundation for grant CHE-1660927.Three-member ring boracyclopropanes (boriranes) with N-heterocyclic carbene substituents were prepared by a recently discovered route. H atoms were selectively abstracted from the boron atoms by t-butoxyl radicals and this enabled boriranyl radicals to be detected and characterized by EPR spectroscopy for the first time. Their EPR parameters indicated they had planar π-character. From competition experiments, the rate constant for H atom abstraction was determined and found to be about 2 orders of magnitude less than for NHC-boranes. The B–H BDE of an NHC-borirane was estimated to be about 95 kcal mol–1.PostprintPeer reviewe

RECENT CASES

Hydride abstraction from monocationic hydride bridged salts [H­(H₂B–L)₂]⁺ [B­(C₆F₅)₄]¯ (L = Lewis base) generates an observable primary borenium cation for L = <i>i</i>Pr_<i>2</i>NEt, but with L = Me₃N, Me₂NPr, or several <i>N</i>-heterocyclic carbenes, highly reactive dicationic dimers are formed