Diazoalkanes from aldehydes

Since the keto component reacts neither with the catalyst 5 (with or without phosphine) nor with the diazoalkane (exceptions below), it is likely to enter the catalytic cycle at the metal-carbene stage 8. If this proposal withstands future mechanistic studies, then the regioselectivity - oxygen to the oxophilic rhenium center-is reasonable by considering a metallacyclic intermediate 10 (eq. (6)). This hypothetical rhena-oxetane is assumed to eliminate the olefin. As a matter of fact, catalyst 5 has been detected from such precursors (e. g., 7a, b -1- diazoalkane f aldehyde) by gas chromatography [9, 10]. 

Condensation with carbonyl compounds. Formation of epoxides from aldehydes by reaction with sulfonium ylides is subject to asymmetric induction. The latter species have been generated from 91, 92, and 93, and also those derived from monoterpenes, e.g., 94 " and 95.- Of course the ylides can be obtained in situ by deprotonation of sulfonium salts or copper-catalyzed decomposition of diazoalkanes (with the carbenoids trapped by the sulfides). 

Hydrazido(2-) and hydrazido(l-) complexes have also been shown to condense with aldehydes and ketones to give diazoalkane complexes containing the W=N—N=CRiR2 unit.387,388 Treatment of these complexes with LiAlFL, gives secondary amines and ammonia, whereas treatment with acid produces hydrazine, keto azines and N2-free tungsten compounds. Amines can also be produced from organohydrazido(2—) complexes.389,390... 

Hydrazido(2-) complexes of Mo and W exhibit nucleophilic behavior and condense with aldehydes and ketones to give diazoalkane complexes (22), but the mechanism of these condensations has not been determined. Loss of tertiary phosphine from hydrazido(2-) intermediates to accommodate a binuclear interaction, as in Scheme 13, or to allow anion coordination are not incompatible. 

The four-coordinate sqnare planar iron(n) porphyrins discussed above are not only of great valne in heme protein model chemistry, but also in chemical applications, since they undergo a wealth of ligand addition reactions. For example it has been shown that TPPFe complexes are active catalysts for important carbon transfer reactions in organic chemistry and are found to catalyze the stereoselective cyclopropanation of aUcenes, olefin formation from diazoalkanes, and the efficient and selective olefination of aldehydes and other carbonyl compounds. The active species in these carbon transfer reactions are presumably iron porphyrin carbene complexes. " It was also found that ferrous hemin anchored to Ti02 thin films reduce organic halides, which can pose serious health problems and are of considerable environmental concern because of their prevalence in groundwater. ... 

Because of the difficulties of purification and handling, many of the results for diazoalkanes have been obtained from reactions in which the diazo compound is not the starting material but in which it may reasonably be supposed to be an intermediate. Most popular in this respect has been the base-catalysed decomposition of arylsulphonyl-hydrazones of aliphatic aldehydes and ketones, a reaction which was first investigated by Bamford and Stevens (1952). Because the reaction... 

The olefination of aldehydes by diazoalkanes depends on catalysts that accept the keto oxygen from the substrate S. and transfer it to an auxiliary reagent R.. A redox process M"=0 is necessarily included in such a sequence (Scheme 3). The reduced step 0=Mo (S2C-NEt2)2 has in fact been isolated from the phosphine reduction of catalyst 4, and a carbene complex of structure 11 according to eq. (7) was suggested [8],... 

Conversion of the aldehyde to protected derivatives at the same level of oxidation (such as ketals, oximes, hydrazones) has been long known. A new hydrazone derived from 4-aminothiomorpholine S,S-dioxide has been carefully investigated [134, 138] and some thiazolidine derivatives have been recently evaluated [136]. C-20 thioketals have been recently introduced, which are especially useful as an aldehyde-protecting group when hydrolysis of the acid-labile mycarose is not wanted their synthesis is accomplished by treatment of the aldehyde with diphenyldisulfide and a trialkylphosphine [134, 139]. The aldehyde has also been transformed into ketones with diazoalkanes [134]. 

Bamford-Stevens and Shapiro Reactions. The Bamford-Stevens reaction is used to obtain unsaturated compounds from tosylhydrazones. A base is required to generate its monoanion, which thermally decomposes to yield the corresponding di-azo derivatives. These reactive species evolve to give an aUcene through carbenium ions in protic solvents or carbenes in aprotic solvents. The thermal decomposition of the monoanions of trisyl-hydrazones is commonly used to obtain diazoalkanes for different applications such as functionalization of solid supports, epox-idation and alkenylation of aldehydes, or the study of radicals and carbenes The functionalization of a Merrifield resin with... 

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