Attempted synthesis

Original Synthesis. The first attempted synthesis of i7-biotin in 1945 afforded racemic biotin (Fig. I). In this synthetic pathway, L-cysteine [52-90-4] (2) was converted to the methyl ester [5472-74-2] (3). An intramolecular Dieckmaim condensation, during which stereochemical integrity was lost, was followed by decarboxylation to afford the thiophanone [57752-72-4] (4). Aldol condensation of the thiophanone with the aldehyde ester [6026-86-4]... 

The latter method typically requires less severe conditions than the former because of the labile nature of the organic anhydride (87,137). Both of these reactions can result in explosions and significant precautions should be taken prior to any attempted synthesis of a peracid (87). For soHd peracids the reaction mixture can be neutralized with sodium hydroxide and the resulting fUtercake washed with water. In the case of the sulfuric acid mediated reaction the peracid has sodium sulfate incorporated in the cake (135). The water of hydration present in the sodium sulfate is desirable to prevent detonation or deflagration of the soHd peracid when isolated in a dry state (87,138,139). 

The smallest member, cyclobutadiene, was the objective of attempted synthesis for many years. The first success was aehieved when cyclobutadiene released from a stable iron complex was trapped with various reagents. ... 

In an attempted synthesis of papaverine based on Rugheimer s preparation of 6 7-dimethoxyisoquinoline from veratrylaminoacetal (McO)2—CjHg—NH—CH2(OEt)2, Allen and Buck reduced deoxy-veratroin oxime, (MeO)2—CgHg—C(NOH)—CHj—C6H3(OMe)2, to a 3-di-(3 4-dimethoxy)-phenylethylamine,... 

The final step in an attempted synthesis of laurene, a hydrocarbon isolated from the marine alga Laurencin glandulifera, involved the Wittig reaction shown. The product obtained, however, was not laurene but an isomer. Propose a mechanism to account for these unexpected results. 

Scheme 1-26. Attempted synthesis of a crown ether-functionalized PTV derivative 76 a) TsO(CH2CH20)3OTs, K2C03i NMP b) LiAlH4, THF c) SOCI2, pyridine. THF d) KOtBu. THF.

Attempted synthesis of RhY(CO)(PPh3)2 in undried solvents (Y = a weakly coordinating anion, e.g. BF4, C104, S03CF3) leads to... 

An attempted synthesis via a retro Diels-Alder route failed, due to the instability of the thiete sulfones at the temperatures required to remove the anthracene blocking group189 (equation 88). 

Compared to polycarbonates, little work has so far been published on the synthesis of poly(iminocarbonates). The first attempted synthesis of a poly (iminocarbonate) was reported by Hedayatullah (44), who reacted aqueous solutions of various chlorinated dipheno-late sodium salts with cyanogen bromide dissolved in methylene chloride. Unfortunately, Hedayatullah only reported the melting points and elemental analyses of the obtained products which, according to Schminke (40), were oligomers with molecular weights below 5000. 

Scheme 31. Attempted synthesis of spirocyclopropanated butadiyne-expanded [n]rotanes from the acyclic precursors 150 and 151...

The first attempted synthesis of a benzo[ ]thiepin derivative was the solvolysis of 7,7-dichloro-3,4-benzo-2-thiabicyclo[4.1,0]heptene (19)20). Unfortunately, the reaction of 19 in hot quinoline led to 2-chloronaphthalene which suggested the reaction mechanism as shown below. In the case of the reaction of l,l-dichloro-7b-ethoxy-... 

Another attempted synthesis of Tc(III)-EDTA and Tc(III)-HEDTA complexes (EDTA ethylenediaminetetraacetic acid HEDTA A -(2-hydroxy-methyl)ethylenediamine-N,AT, iV -triacetic acid) was carried out using [Tc(tu)6]3+ as the starting complex [40]. Technetium-EDTA complexes have been synthesized by the direct reduction of pertechnetate with a suitable reduc-tant in the presence of excess EDTA [41-43]. On addition of EDTA to the Tc(tu) + solution, the intensity of the absorption spectrum decreased with time and the solution color changed from reddish orange to light brown. An electrophoretic analysis for the Tc(III)-EDTA complex showed that more than 70%... 

With l,3>5-cycloheptatriene 2 can be trapped to yield four isomeric [2+2] adducts and the exo/endo isomeric [6+2] compound 16. Heating this mixture to 110°C leads to the complete transformation of the silacyclobutanes into 16 via a dipolar intermediate. The attempted synthesis of the diphenyl derivative of the [2+2] products leads to the stereospecific formation of endo-Yl which could be characterized by X-ray diffraction analysis [4]. 

Scheme 13 Attempted synthesis of phosphaquinoid compounds carrying m-terphenyl ligand [13]...

An example occurs in the attempted synthesis of a CHC1 complex which immediately undergoes metallacycle formation (99) ... 

Additionally, we believe that the olefin is not free to rotate and rotamer issues may arise in an attempted synthesis. In Box-C, the cis-methyl groups at C6 and C7... 

An attempted synthesis, Scheme 65, of a heterozincate from dimethylzinc and bis (2-pyridyl)methyl lithium gave instead the dimeric [bis (2-pyridyl)methyl methylzinc] complex 84, shown in Figure 43.143 The intermolecular zinc-carbon bond to the bridging carbon atoms is remarkably short (2.269(3) A), while the zinc-methyl bond is slightly elongated (1.974(3) A). 

In the structure refinement of LiZn2Mo30g the Li ions were not located because of their apparent scrambling with Zn ions in both the tetrahedral and octahedral sites. An effort to overcome this difficulty was made with the attempted synthesis of NaZn2Mo308, where it was expected that the Na+ ions would be confined only to the octahedral sites. This attempted synthesis led instead to the formation of the new compound NaMo Og (19) which grew in the reaction mixture and on the wall of the molybdenum container as thin needles with silvery metallic luster. 

An unusual mixed lithium phosphide/lithium alkyl aggregate has been reported as arising from an attempted synthesis of Li PH(mes ) (46). Initial treatment of phosphorus trichloride with Li(mes ) is reported to give a mixture of the desired product, (mes )PCl2, and the side product (mes )Cl (via Li/Cl exchange) in an approximately 2 1 ratio. Reduction of this mixture with LiAlH4, followed by treatment with BuLi, then leads to rapid formation of Li PH(mes ), accompa-... 

Polycondensation of Bisphenols, II, with Phosgene. Polycondensation of siloxane-linked bisphenols, II, with phosgene is the most obvious synthetic approach leading to siloxane-modified poly(arylene carbonates) since the phosgene-bisphenol polycondensation is used in the synthesis of aromatic polycarbonates (1). This method was used initially to prepare polymer (as indicated in reaction 1) as well as for the attempted synthesis of polymers 2 and 5 ... 

An attempted synthesis of 1-isopropyl-4,8-dimethyl-azulene. Migration of... 

---