bluuebunny/crossref_metadata_2025_split huggingface dataset:
Oxidative Nucleophilic Substitution of Hydrogen in Nitroarenes
Authors: Makosza Mieczyslaw , Staliński Krzysztof 
Published: July 2007

AbstractCarbanions of 2‐phenylpropionitrile were found to add to nitroarenes in liquid ammonia to form σH adducts, which were oxidized with KMnO4 to yield products of oxidative nucleophilic substitution of hydrogen (ONSH) in the position para to the nitro group. Treatment of the carbanion‐nitroarene system with methyl iodide at ‐70°C indicated that the addition proceeds almost to completion. Thus, for the first time, the persistence of σH adducts, formed between free anions and mononitroarenes, has been demonstrated. It was also shown that KMnO4 oxidizes σH adducts to nitrobenzene faster than it does carbanions. This selective ONSH in the para positions of nitroarenes is a general process. However, some substituents hinder or inhibit the oxidation step.
Electroanalysis Utilizing Amperometric Microdisk Electrode Arrays
Authors: Ordeig Olga , del Campo Javier , Muñoz Francesc Xavier , Banks Craig E. , Compton Richard G. 
Published: July 2007

AbstractThis article reviews the literature dealing with electroanalytical applications of ultramicroelectrode arrays over the past twenty years. A brief theoretical description of the mass transport mode governing their behavior is given, after which the main fabrication methods are described. The applications described in the later sections of this review range from conventional electroanalysis, namely trace metal stripping methods, using mercury modified arrays to more recent advances in the field of biosensors (enzymatic, immunosensors and nucleic acid based ones).
Chiral organometallic reagents, XII. On the racemization of α‐hetero‐substituted benzyllithium compounds
Authors: Ahlbrecht Hubertus , Harbach Jürgen , Hoffmann Reinhard W. , Ruhland Thomas 
Published: July 2007

AbstractBenzyllithium compounds carrying a benzylthio substituent (6), a benzylseleno substituent (8), and an isopropyl(methyl)amino substituent (14) have been generated. Racemization barriers have been determined in THF by monitoring the coalescence of signals of diastereotopic groups in the 1H‐NMR spectra. The barrier for 6 amounts to a ΔH≠ of 7.5 kcal mol−1 and ΔS≠ of −12 cal mol−1 K−1 corresponding to a ΔG of 9.9 kcal mol−1. The barrier for the other compounds investigated varies from 9 to 10 kcal mol−1. The rate‐determining step for the racemization is discussed to be the transformation of the contact ion pair to the solvent‐separated ion pair.
1,3‐dipolar cycloaddition of diphenylnitrilimine to substituted dihydro‐3‐methylene‐2(3H)‐furanones
Authors: Štverková Slávka , Žák Zdirad , Jonas Jaroslav 
Published: July 2007

AbstractSubstituted 4,5‐dihydro‐3‐methylene‐2(3H)‐furanones 1 react as dipolarophiles with diphenylnitrilimine to give the corresponding spiro[furan‐pyrazolin]ones 2. From the compound 1a, 1,3‐diphenyl‐7‐oxa‐1,2‐diazaspiro[4,4]non‐2‐en‐6‐one (2a) is formed. In the other cases, a primarily formed cycloadduct undergoes rearrangement during the reaction to the bicyclic compound 5. Thus, addition of diphenylnitrilimine to (E)‐1b, (Z)‐1b and (E)‐1c leads to compound 5b, whereas reactions of (E)‐ or (Z)‐1f and (E)‐1g give the corresponding compound 5f and 5g, respectively. The structure of 5b was determined by X‐ray analysis. Labeled methyl formate (H13CO2CH3) was used for labeling the methylene carbon atom in 4,5‐dihydro‐3‐(p‐tosyloxymethylene)‐2(3H)‐furanone [(E)‐1b] in order to ascertain the structure of the intermediate cycloadduct as well as the pathway of the consecutive rearrangement.
Biologically active glycosides from asteroidea, XXXII. Glycosphingolipids from the starfish Astropecten latespinosus, 2. Structure of two new ganglioside molecular species and biological activity of the ganglioside
Authors: Higuchi Ryuichi , Matsumoto Shuji , Fujita Masanori , Komori Tetsuya , Sasaki Takuma 
Published: July 2007

AbstractTwo ganglioside molecular species [LG‐1 (1) and LG‐2 (5)] have been obtained from the water‐soluble lipid fraction of the chloroform/methanol extract of the starfish Astropecten latespinosus. On the basis of chemical and spectroscopic findings, the structure of 1 and 5 have been elucidated. They are new ganglioside molecular species. Negative FAB mass spectrometry provided important information both on the structure of the sugar moiety and on the molecular mass of the gangliosides. Partial hydrolysis by hot water has proved useful for structure elucidation of the complex oligosaccharide moieties. In addition, the major ganglioside molecular species, LG‐2 (5), shows antitumor activity against murine lymphoma L1210 cells in vitro.
Stereochemistry of 2‐methyl‐ and 2‐phenyl‐2‐adamantyl cations
Authors: Herrmann Roland , Kirmse Wolfgang 
Published: July 2007

AbstractWhen both diastereomers of [5‐D]‐2‐methyl‐2‐adamantyl 2,4‐dinitrophenolate (18a) and [5‐D]‐2‐phenyl‐2‐adamantyl 2,4‐dinitrophenolate (18b) were solvolyzed in 40% aqueous acetone, 1:1 mixtures of (E)‐ and (Z)‐[5‐D]‐2‐R‐adamantan‐2‐ols (19a, b) were obtained. The stereoselectivity of secondary 2‐adamantyl cations, attributed to σ participation, is effectively suppressed by charge‐stabilizing groups at C‐2.
Addition and cyclization reactions in the thermal conversion of hydrocarbons with enyne structure, I. Detailed analysis of the reaction products of ethynylbenzene
Authors: Hofmann Jörg , Zimmermann Gerhard , Guthier Klaus , Hebgen Peter , Homann Klaus‐Heinrich 
Published: July 2007

AbstractThe pyrolysis of ethynylbenzene (C8H6, 1) was studied in a flow system between 700 and 1100°C (reaction time about 0.3 s) by using a mixture of 5 mol‐% of 1 in nitrogen and also in hydrogen at 700°C. The products were analyzed gas chromatographically. At 700°C in nitrogen, the main products were 1‐ and 2‐phenylnaphthalene (2, 3), 1‐methylene‐2‐phenyl‐1H‐indene (4), 1‐methylene‐3‐phenyl‐1H‐indene (5), and 5,10‐dihydroindeno[2,1‐α]indene (6). At higher temperatures, ethynylaromatics and more stable aromatics such as benzene, naphthalene, acenaphthylene, biphenyl, pyrene, fluoranthene, and six further C16H10 isomers where detected. With hydrogen as diluent, the dimer formation was reduced, mainly in favor of styrene. – The complex mixture of reaction products and the dependence of its composition on the pyrolysis temperature cannot be explained in terms of one reaction scheme only. It is suggested that H atoms act as important chain carriers. At temperatures around 700°C they mainly add to 1 yielding the phenylvinyl radicals 1a and 1b. These add to 1 forming dimers C16H12 via radicalic intermediates C16H13. With increasing temperature the 2‐phenylvinyl radical 1a not only reacts back to H + 1 but also decomposes by β(CC) cleavage into phenyl and ethyne. The latter channel is more endothermic by 33 kJ/mol. Additionally, isomeric ethynylphenyl radicals are increasingly formed by bimolecular H abstraction. Thus, with increasing temperature product formation is controlled by reactions of phenyl‐type radicals.
1‐ and 2‐fluoroalkyl carboxylates
Authors: Limat Dominique , Guggisberg Yves , Schlosser Manfred 
Published: July 2007

AbstractThe 2‐fluoroalkyl esters (1–4) of carboxylic acids are readily accessible by the base‐catalyzed acylation of fluorohydrines. A two‐step procedure is required to prepare the 1‐fluoroalkyl esters (10–14, 16): conversion of alk‐1‐enyl carboxylates („ene esters”︁) into the 2‐bromo‐1‐fluoroalkyl esters 5–9, 15, 17–19 by simultaneous treatment with N‐bromosuccinimide and hydrogen fluoride followed by the reductive replacement of bromine by tributyltin hydride. Alka‐1,3‐dienyl carboxylates („diene esters”︁) undergo 1,4‐addition of bromine and fluorine. The resulting 4‐bromo‐1‐fluoroalk‐2‐enyl carboxylates 20–25 undergo a substitution reaction with sodium benzenesulfinate to afford the sulfones 26–28 or oxidation with dimethyl sulfoxide to yield the 4‐oxo derivatives 29–30.
First stereoselective synthesis of (1S,2S,4R,5R)‐(−)‐β‐multistriatin
Authors: Henrichfreise Peter , Scharf Hans‐Dieter 
Published: July 2007

AbstractStarting from 2,3‐O‐(3‐pentylidene)‐D‐glyceraldehyde (3), we prepared the bicyclic pheromone (1S,2S,4R,5R)‐(−)‐β‐multistriatin (1) on a gram scale. Key steps of the synthesis are a cis‐selective Wittig olefination followed by diastereo‐selective Michael addition and hydrogenation.
A convenient enantioselective synthesis of (R)‐(−)‐phoracantholide I, a component of the defensive secretion of the eucalypt longicorn Phoracantha synonyma
Authors: Enders Dieter , Plant Andrew , Drechsel Karin , Prokopenko Oleg F. 
Published: July 2007

AbstractA short enantioselective synthesis of phoracantholide I [(R)‐4] (ee = 91 %), a component of the defensive secretion of the eucalypt longicorn Phoracantha synonyma, is described. Key steps of the synthesis are the enantioselective α‐alkylation of cyclononanone SAMP hydrazone [(S)‐1] (de > 93%) and subsequent Baeyer‐Villiger reaction of the ketone (R)‐3 with retention of configuration.
Efficient, simple procedures for the large‐scale preparation of building blocks for angiotensin (II) receptor antagonists
Authors: Jendralla Heiner , Wagner Adalbert , Mollath Martina , Wunner Joachim 
Published: July 2007

AbstractThe kg‐scale syntheses of p‐formylbenzeneboronic acid 3c and the biphenyl derivatives 4a, 4b, and 4c, building blocks for angiotensin (II) receptor antagonists, are reported.
New chiral building blocks from 1,2;5,6‐di‐O‐isopropylidene‐D‐mannitol: Synthesis of C2‐symmetrical and unsymmetrical mono‐ and bisepoxides and of a polyhydroxylated butenolide
Authors: Mulzer Johann , Pietschmann Catarina , Schöllhorn Bernd , Buschmann Jürgen , Luger Peter 
Published: July 2007

AbstractThe enantiopure epoxides 2–6 were synthesized from 1,2;5,6‐di‐O‐isopropylidene‐D‐mannitol (1). The terminal epoxides 2 and 3 are available from the desoxy mannitol 9 in three steps. The C2‐symmetrical epoxides 4 and 5 were generated via the C‐4‐inverted alcohol 15. The C2‐symmetrical bisepoxide 6 was prepared in a short sequence maintaining the symmetry throughout the entire synthesis. The crystalline butenolide 44 was prepared in five steps from 1 by Wittig olefination and lactonization.
Cycloadditions, 53. New spirocyclic chiral dienes — synthesis and diastereoselective Diels‐Alder reactions with N‐phenylmaleimide
Authors: Hoffmann Ralf , Mattay Jochen 
Published: July 2007

AbstractSynthesis and diastereoselective Diels‐Alder reactions of new spirocyclic chiral dienes are reported. Starting with diketene and (−)‐menthone (1), we prepared the diastereomeric diketene‐menthone adducts 2 and 3. Further derivatization and olefination afforded four chiral dienes 12‐15. Diastereoselective Diels‐Alder reactions of these dienes with N‐phenylmaleimide (NPM) under high‐pressure conditions yielded the corresponding cycloadducts 16‐19. Olefination of 6‐diethylphosphonomethyl‐2,2‐dimethyl‐1,3‐dioxin‐4‐one 8 with formaldehyde led to unexpected compounds 9‐11 resulting from the originally formed olefination product.
Chiral calixarenes derived from resorcinol
Authors: Iwanek Waldemar , Mattay Jochen 
Published: July 2007

AbstractA new type of chiral resorc[4]arene is described. The formation of both enantiomers of 5 is controlled by the chirality of the amines used in the Mannich reaction leading to the 1,3‐oxazine ring anellated to the resorcarene moiety. At −50°C ee increases up to 90%. Both enantiomers can be easily purified to >98% ee by recrystallization. The structures were proved by standard methods including X‐ray analysis.
Cyclophanes, XL. On the preparation of conjugated polyenes with [2.2.2]paracyclophanyl end groups
Authors: Heirtzler Fenton R. , Hopf Henning , Lehne Verena 
Published: July 2007

AbstractModel substances for oligomeric systems based on the incorporation of [2.2.2]paracyclophane into the repeating unit are linear polyenes bearing a paracyclophanyl residue in the terminal positions. The preparation of the polyenes 2a–c is described. In addition to the characterisation as diarylpolyenes, consideration of model compounds revealed that the [2.2.2]paracyclophanyl residues interact with pendent substituents according to a magnetic anisotropic mechanism.
Diastereoselective side‐chain alkylation of (prolinolylmethyl)oxazoles and ‐oxadiazoles
Authors: Pohl Martin , Thieme Marion , Jones Peter G. , Liebscher Jürgen 
Published: July 2007

AbstractDiastereoselective alkylation of the α‐position of (S)‐(prolinolylmethyl)oxazoles and ‐oxadiazoles 1 leading to side‐chain modified products 2 and 3 was achieved by reaction with LDA and alkylating agents or aldehydes. The products 2 and 3 are precursors of non‐natural chiral α‐amino acids. The influence of substituents, reagents, and reaction conditions on the diastereoselectivity of the alkylation was investigated. A model was proposed explaining the stereochemical outcome of the reaction. Corresponding α‐acylation of prolinolylmethyl heterocycles 1 with chloroformates affording chiral α‐amino esters 4 were not stereoselective.
On the formation of N‐heterocycles by Thermolysis of conjugated α‐azidoacrylates
Authors: Vogel Claus , Delavier Paul , Schnippenkötter Bernd 
Published: July 2007

AbstractThe synthesis of various o‐butadienyl‐α‐azidocinnamates 2 and β‐cycloalkenyl‐α‐azidoacrylates 9 is described. The thermolysis of compounds 2 in solution yields the new 8,9‐benzo‐6‐azabicyclo[3.2.2]nona‐3,6,8‐trienes 3 as major products, while that of 9 yields the cycloalkano‐2H‐pyrroles 10, which can rearrange to the cycloalkano‐1H‐pyrroles 11 at higher temperatures. A β‐(o‐vinyl)phenanthryl‐α‐azidoacrylate 12 was found to react on thermolysis both as a β‐cycloalkenyl‐α‐azidoacrylate and a o‐vinyl‐α‐azidocinnamate.
An unexpected product in attempted [4 + 2] cycloadditions of 2,2‐diethyl‐4,5‐dimethyl‐2H‐imidazole
Authors: Felderhoff Michael , Sustmann Reiner , Steller Ingo , Boese Roland 
Published: July 2007

Abstract2,2‐Diethyl‐4,5‐dimethyl‐2H‐imidazole 1, formally a 1,4‐di‐azadiene, does not produce [4 + 2] cycloadducts with various electronically‐different dienophiles. In the presence of tri‐fluoroacetic acid, it tautomerizes to 2,2‐diethyl‐4‐methyl‐5‐methylene‐3‐imidazoline 2 and forms a dimer, the structure of which was determined by X‐ray crystallography.
Ab Initio Molecular Orbital Calculations on Allylic 1,3‐Strain of Electron‐Donor‐ and Electron‐Acceptor‐Substituted Alkenes
Authors: Tietze Lutz F. , Schulz Gerhard 
Published: July 2007

AbstractAb initio calculations on the conformations of several electron‐rich and electron‐poor alkenes 2, 8–15 were performed up to the MP2/6–31G*/RHF/6–31G* level. It was proven that allylic 1,3‐strain can be traced back to steric interactions between the allylic center and the (Z) substituent of the double bond. The electron density of the double bond seems to have no effect on the difference in energy between the global and the local minimum. The local minimum (180° conformation) of (Z)‐methyl‐substituted alkenes 2, 14 and 15 carrying a methyl, carboxyl and methoxy group, respectively, at the double bond in (E) position, lies 3.37–3.52 kcal/mol above the 0° conformation (global minimum); thus, the (E) substituent has no significant influence on this energy difference and therefore on the equilibrium distribution.
Chiral Tri‐ and Pentamethinium Cyanine Dyes with 1,2,3,4‐Tetrahydro‐6‐methylquinolyl End Groups: UV/Vis and CD Spectroscopy and Structure Correlations
Authors: Buß Volker , Ulbrich Dagmar , Reichardt Christian 
Published: July 2007

AbstractUV/Vis and CD spectra of the chiral trimethinium cyanine dyes T2 to T5 and the pentamethinium cyanine dyes P2 to P5 have been studied for possible correlations between chiroptical properties and molecular structure. With a non‐planar conjugated π‐system as a consequence of steric interaction between the two end groups and the polymethine chain and with the methyl substituents in the 2‐ or 3‐ring positions acting as chiral anchors, the inherent chirality of these dyes manifests itself in the CD spectra which follow the same pattern throughout: monosignate CD absorptions in the long‐wavelength cyanine band region and bisignate in the aromatic‐end‐group region. A correlation between the sense of twist of the polymethine chain and the observed and calculated sign of the cyanine band is established, which allows the assignment of the absolute configuration for the 2‐, but not for the 3‐methyl substituted dye derivatives. Neither in the trimethinium nor in the pentamethinium dyes do the calculated energies, geometries or chiroptical properties indicate any interaction between the two end groups.
Asymmetric Strecker Synthesis of the Four α‐Quaternary 1‐Amino‐2‐methylcyclohexanecarboxylic Acids
Authors: Volk Franz‐Josef , Frahm August Wilhelm 
Published: July 2007

AbstractThe synthesis of the four 1‐amino‐2‐methylcyclohexanecarboxylic acids 13, 14, 15, and 16 from diastereomeric mixtures of the α‐amino nitriles 1–4 by successive application of conc. H2SO4, Pd/C H2, and conc. HCl is described. The amino nitriles 1–4 were prepared by asymmetric Strecker synthesis under various reactions, The formation of 1–4 is thermodynamically controlled in protic solvents (e.g. MeOH), whereas the reaction is under kinetic control in non‐protic solvents (e.g. hexane), The separation of the α‐amino amides 5–8, which were obtained by partial hydrolysis of 1–4, was achieved by CC, LPLC, and HPLC. The absolute configuration of all synthesized compounds was determined by means of only two X‐ray analyses with consecutive correlations. The steric control of the asymmetric Strecker synthesis is discussed.
Rearrangement of Donor‐Acceptor‐Substituted Vinylcyclopropanes to Functionalized Cyclopentene Derivatives: Evidence for Zwitterionic Intermediates
Authors: Buchert Matthias , Reißig Hans‐Ulrich 
Published: July 2007

AbstractDonor‐acceptor‐substituted vinylcyclopropanes such as 1a, 3a, 5a, 5b, 7a, 9a, 9b, and 12a smoothly undergo thermal ring enlargement to functionalized cyclopentene derivatives 2, 4, 6, 8, 10, and 13 at relatively low temperatures (150–190°C) in good yields. This vinylcyclopropane‐cyclopentene rearrangement proceeds with low (1a, 3a), moderate (9a, b) or high (7a, 12a) stereoselectivity. In the case of 7a and 12a almost complete retention of configuration with respect to the migrating (methoxy) (phenyl)‐substituted carbon atom was observed. The definite mechanistic interpretation of these results is complicated by the stereoisomerization of the starting donor‐acceptor‐substituted vinylcyclopropanes which proceeds as competing reaction during ring enlargement. Nevertheless, all observations together, in particular the recorded solvent effects, support a stepwise mechanism of the rearrangement with a highly stabilized 1,3‐zwitterionic species as common intermediate for cyclopropane stereoisomerization and ring enlargement.
Aromatic Sulfonation, 130. – Relative Intramolecular Reactivity of the Insulated π Double Bond and the 14π Annulene Perimeter toward Sulfur Trioxide in the Sulfonation of Isopyrenes
Authors: Cerfontain Hans , Bakker Bert H. , Koeberg‐Telder Ankie , Wilmes Oswald 
Published: July 2007

AbstractThe sulfonation of isopyrene (1) and its 5‐methyl‐ and 5,10‐dimethyl derivative 2 and 3 with SO3 in both dichloromethane and nitromethane as solvent has been studied. Reaction of 1 and 2 leads to sulfodehydrogenation in which SO3 reacts as a monodentate electrophile, the initial products being 1‐5‐sulfonic acid (1‐5‐S) and 2‐10‐S, respectively. In the presence of a sufficiently large amount of SO3 1‐5‐S is subsequently converted into 1‐5,10‐S2. With 3, using 2.0 molequiv, of the sulfonating reagent in dichloromethane, the SO3 adds as a bidentate electrophile to the “central C=C bond” with formation of 7,14‐dimethyl‐1,6:8,13‐ethanediylidene‐[14]annulene‐15,16‐sultone (5) and the corresponding pyrosultone 6. Upon subsequent hydrolysis and neutralization with aqueous KOH the eventually obtained product is potasium 16‐hydroxy‐7,14‐dimethyl‐1,6:8,13‐ethanediylidene‐[14]annulene‐15‐sulfonate (4).
Oligomerization and Polymerization in Sodium Salts of Chlorocarboxylic Acids
Authors: Epple Matthias , Kirschnick Holger 
Published: July 2007

AbstractHeating of the sodium salts of chlorocarboxylic acids leads to exothermic elimination of sodium chloride and oligomerization of the organic backbone of the molecule. Thermochemical data of sodium 2‐chloropropionate (1), sodium 3‐chloropropionate (2) and sodium 2‐chlorobutyrate (3) were derived. The reaction products were characterized by IR and NMR spectroscopy, and the degree of polymerization was determined by gel permeation chromatography (GPC).
Towards the Synthesis of o‐Diphosphaquinones: Benzodiphosphadihydropentalene – Naphthodihydrodiphosphete
Authors: Märkl Gottfried , Hennig Rüdiger , Nöth Heinrich 
Published: July 2007

Abstracto‐Quinodimethanes 1 are important intermediates in organic synthesis that may be generated by thermal valence isomerization of benzocyclobutenes[1] or octa‐1,2,4,6,7‐pentaenes[2]. The preparation of a stable o‐quinodimethane has not been reported so far. Whereas o‐quinodiimines 2 containing strongly electron‐withdrawing groups at the nitrogen atoms are isolable[3], o‐diphosphaquinones 3 have not been detected.
Substituent Effects on the CC Bond Strength, 20. – Geminal Substituent Effects, 14. – Stabilization of the Cyano(dimethylamino)methyl Radical – Synergistic effect Due to Interaction Between α‐Amino and α‐Cyano Groups on the Radical Stabilization Energy
Authors: Welle Frank M. , Verevkin Sergey P. , Beckhaus Hans‐Dieter , Rüchardt Christoph 
Published: July 2007

AbstractThe thermolysis reactions of 3a and 2a, b were studied over a temperature range of 40°C and the activation parameters were determined. They were compared with the activation parameters of structurally comparable hydrocarbons of similar strain in order to obtain the radical stabilization enthalpies RSEs of the cyano(dimethylamino)methyl radical 1a. For this comparison the geminal interaction enthalpies of the cyano and the dimethylamino groups in the ground state had to be determined for the series of amino nitriles 4a–4c and 4j–4n by thermochemical methods. The geminal interaction in the ground state varies between −0.6 kcal/mol stabilization in 4a and a destabilization of +10.7 and +7.0 kJ mol−1 for secondary and tertiary α‐dialkylaminonitriles, respectively. A synergistic (i.e. more than additive) stabilization enthalpy of 26 kJ mol−1 of 1a was found in contrast to predictions in the literature. This stabilization is interpreted by conjugation between the substituents, which are separated by the radical center.
Sterically Congested Molecules, 17. – Novel Syntheses of α,α,β‐Tri‐tert‐butyl Compounds
Authors: Böhrer Gerald , Knorr Rudolf , Böhrer Petra , Schubert Bernhard 
Published: July 2007

AbstractPivaloin (2), prepared from ethyl pivalate (1) or from dimethyl oxalate (3), reacts with tert‐butyllithium by reduction (45% of 10) and addition (45% of 9), whereas the corresponding Barbier variant takes a different course. Productive transformations of the α,α,β‐tri‐tert‐butyl glycol 9 lead to α,β,β‐tri‐tert‐butylethanone (17, overall 4 steps), or α,α,β‐tri‐tert‐butylethene (20, 3 or 4 steps), or α,β,β‐tri‐tert‐butyl‐β‐hydroxyethanone (19, 3 steps, also by Grignard addition to bipivaloyl 4). Steric congestion is assessed by searches for restricted internal rotation. The alkene 20 and its epoxide 27 are studied with respect to NMR assignments and chemical degradation.