Alkylation-oxidation sequence

A stereospecific selenoamination-alkylation-oxidation sequence has been applied to the properly positioned hexenylaniline system (465) to yield, by reaction with A-phenylselenonaphthalimide N-PSP) a diastereomeric mixture of selenides (466) which, upon oxidative deselenylation produced a 4 1 mixture of compounds (467) and (468) in 45% overall yield (Scheme 34) <85JA389i>. 

Alkylation-oxidation sequence. Organozirconocene chlorides add to aliphatic and aromatic aldehydes (ZnEr catalyzed). Oppenauer oxidation occurs when the reaction time is prolonged. 

Since the formation of optically active, dioxolanone-based di-enolates was not successful, a consecutive alkylation strategy was developed for a short synthesis of (-)-wikstromol (ent-3) from (-)-malic acid (99) (Scheme 25). The first alkylation reaction was analogous to that reported for the enantioselective total synthesis of (-)-meridinol (97). In order to avoid a reduction/re-oxidation sequence and an almost unselective second alkylation, two disadvantages of the synthesis of meridinol (97) [55], we planned to use a different strategy for the second alkylation. Therefore, we have focused our strategy on two stereoselective alkylation reactions, one of dialkyl malates and one of a dioxolanone prepared thereof. Both alkylation reactions were previously described by Seebach and coworker [56, 63, 64]. The... 

You may have noticed that only one of the three alkyl groups of a trialkyl-borane is converted to an aldehyde by the carbonylation-reduction-oxidation sequence. To ensure that carbonylation takes the desired course without wasting the starting alkene, hydroboration is achieved conveniently with a hindered borane, such as 9-BBN, 12. With 12, only the least-hindered alkyl group rearranges in the carbonylation step ... 

Alkaline hydrogen peroxide does not attack alkyl side chains directly, but it can be very useful for the conversion of the aromatic aldehyde to the carboxylic acid in the side chain oxidation sequence. The chemistry is covered in Section 6.1. Peracids usually do not attack alkyl side chains, but can oxidize benzylic alcohols and aldehydes to the carboxylic acids and benzylic ketones to phenyl ester. These reactions are covered in sections on alcohol (5), aldehyde (6.1) and ketone (6.2) oxidation. 

Aldehydes provide a ready example of organic molecules capable of undergoing disproportionation reactions, because they occupy the midway position in the oxidation sequence from primary alcohols to carboxylic acids. However, they are not the only examples of organic species that are capable of undergoing disproportionation. All that is necessary is to find a species that occupies a similar midway position in some redox sequence e.g. suggest what is the disproportionation reaction which occurs between two alkyl radicals. 

Alkylation of iV-oxides usually takes place firstly at the oxygen <895773,905795,91CHE802) as does acylation <89TL4353, 905795>. In order to obtain 3-alkylimidazole 1-oxides an acylation-alkylation-deacylation sequence can be followed (Scheme 118) <905795). 

By analogy with Grignard reagents, other nucleophiles can be introduced into 1,2,4-triazines in an addition/oxidation sequence giving a formal substitution of hydrogen. This holds particularly for ammonia, hydrazine, hydrogen cyanide, and sulfur dioxide. Also examples involving preactivation of the triazine system by protonation or alkylation are discussed in Section 2.2.1.5.5. 

Assuming pressure-dependent diastereoselectivity to be primarily caused by differences in steric interaction of the two diastereomeric transition structures and not by a change in reaction mechanism, an increase in — AAV with increasing bulkiness of the substituents and was anticipated. The dienes 93a-c were prepared in a three-step sequence starting from trans-cinnamaldehyde by alkylation, oxidation and Wittig reaction. The cycloadditions were carried out in toluene... 

The core skeleton of geissoschizine, an important biosynthetic precursor to numerous polycyclic indole scaffolds, was the target of a nickel-catalyzed alkylative coupling strategy. Cyclization precursor 13 was prepared by ozonolysis and double reductive amination of cyclopentene 12 (Scheme 8.13) [35]. Nickeldeprotection/oxidation sequence followed, and chromatography led to complete inversion of the C3 stereocenter. A Fisher indole synthesis followed to afford ( )-deformyl-isogeissoschizine, the core skeleton of geissoschizine. 

Acylsilanes are yet another class of valuable synthetic intermediates, and new methods for their synthesis are always welcome. In the first of several examples reported this year, the silyl allene (168) has been used as a common intermediate for the preparation of a diverse range of acylsilanes with a,p-olefinic, a,p-acetylenic, and a-keto substituents. Alkyl-substituted acylsilanes are now available via a high-yielding process in which an acyl-lithium (generated in situ from an alkyl-lithium and CO) is trapped by MeaSiCl. Cyclic acylsilanes have been prepared from cyclic vinylsilanes by way of an epoxidation-reductive ringopening-oxidation sequence. ... 

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