1 aldehyde protection aldehydes

A new solid phase method to synthesize libraries of compounds based on 1,2,5-thiadiazolidine heterocycle was developed (00TL(41)3161). Starting from the coupling of the protected aminoacid to the resine functionalized with p-alkoxybenzylalcohol as the linker, a series of sulfahydantoins 251 could be obtained. The method is applicable to aminoacids with a basic side chain, aliphatic aldehydes or aldehydes with basic functionalities. 

With respect to the nucleophilic addition of organocopper reagents, a sharp contrast between the rigid isopropylidene glyceraldehyde and its open-chained analog, 2,3-bis(benzyloxy)propanal. was observed (compare Tables 15 and 16). With the isopropylidene-protected aldehyde a high syn diastereoselectivity could only be obtained when tetrahydrofuran was used as reaction solvent, and the diastereoselectivity dropped considerably in diethyl ether. In contrast, the latter solvent allows excellent syn selectivities in additions to the dibenzyl-protected glyceraldehyde81. On the other hand, tetrahydrofuran yields better results than diethyl ether in the... 

How would you make the half protected aldehyde (12 given that (11) is available from the reaction shown. 

To make (18), we must reduce the ester in the presence of the aldehyde protection is necessary and an acetal the obvious way. 

Conversion to acetals is a very general method for protecting aldehydes and ketones against nucleophilic addition or reduction.245 Ethylene glycol, which gives a cyclic dioxolane derivative, is frequently employed for this purpose. The dioxolanes are usually prepared by heating a carbonyl compound with ethylene glycol in the presence of an acid catalyst, with provision for azeotropic removal of water. 

In general, the methods for protection and deprotection of carboxylic acids and esters are not as convenient as for alcohols, aldehydes, and ketones. It is therefore common to carry potential carboxylic acids through synthetic schemes in the form of protected primary alcohols or aldehydes. The carboxylic acid can then be formed at a late stage in the synthesis by an appropriate oxidation. This strategy allows one to utilize the wider variety of alcohol and aldehyde protective groups indirectly for carboxylic acid protection. 

Treatment of the protected aldehyde 342 with a TFA/water/chloroform mixture results in the formation of a 10-membered intermediate iminium cation intramolecular attack of this electrophile at C-2 of the indole (an intramolecular Pictet-Spengler reaction) gives the isolated tetracyclic product 343 in good yield (Equation 124) <1995T4841>. 

The potentiality of the present methodology is demonstrated by the synthesis of y-undecalactone, as shown in Scheme 18 [37,47], The treatment of the THP-protected cu-hydroxyalkyl iodide with the anion of methoxybis(trimethylsilyl) methane gave the corresponding alkylation product. Acidic deprotection of the hydroxyl group followed by Swern oxidation produced the aldehyde. The aldehyde was allowed to react with heptylmagnesium bromide, and the resulting alcohol was protected as tm-butyldimethylsilyl ether. The electrochemical oxidation in methanol followed by the treatment with fluoride ion afforded the y-undeealactone. 

The specific glove and protection requirements are Chemical type Is aldehyde Protection time requirement In minutes Is 200 Tactlllty requirement Is moderate tactile... 

We investigated the possibility that the N-linked 2-methylimidazole ring might not be the optimum one for 5-HT3 antagonist activity and considered the possibility that C-linked imidazole derivatives might have advantages. One of the first compounds prepared was the indolyl ketone (27), which was chosen on grounds of accessibility and synthesized by standard reactions from the protected aldehyde (26) (Scheme 7.4) [61]. 

Scheme 1. Principle of cyanine dye synthesis leading to trimethine (n = l), pentamethine (n = 2) and heptamethine (n = 3) chromophores. Structures comprising indolic subunits are usually named indocarbocyanine, indodicarbocyanine and indotricarbocyanine, respectively. Formic acid, malonic aldehyde, glutaconic aldehyde are used in their protected dianUide or orthoester form. They can be applied as substituted derivatives to introduce residues into the polymethine unit. The indolic substructure might bear further residues or annelated aromatic rings...

The aldehyde-aldehyde aldol reactions were first nsed in a natural product synthesis setting by Pihko and Erkkila, who prepared prelactone B in only three operations starting from isobutyraldehyde and propionaldehyde (Scheme 40). Crossed aldol reaction under proline catalysis, followed by TBS protection, afforded protected aldehyde 244 in >99% ee. A highly diastereoselective Mukaiyama aldol reaction and ring closure with aqueous HE completed the synthesis [112]. 

The alkenes 149 and 150 are easily cleaved by ozonolysis either directly or after protection of the hydroxy gronp. Depending on the workup conditions of the ozonolysis, either diols 151 or 0-protected aldehydes 152 can be obtained. The C2 symmetric ketone 153 dr 75 25) is available from another addition of the dilithium reagent 148 (R = Ph)... 

Annulation of the pyrrole ring. o-Aminoketone 179, bearing the protected aldehyde moiety, can be smoothly reacted with substituted phenyl alanines and transformed into 1,4-benzodiazepinones 180 with a fused pyrrole ring (Scheme 36 (1992BMCL1639)). 

Since a-branched aldehydes gave rather higher asymmetric induction (Scheme 6.166), Nagasawa et al. extended the biphasic strategy to the diastereoselective Henry reaction of nitromethane with enantiomerically pure (S)-configured N,N -dibenzyl protected a-amino aldehydes and a-hydroxy aldehydes protected as silyl ethers. The screening reaction (Scheme 6.169) demonstrated a match/mismatch... 

Displacement of the methylthio group can also be performed with alkoxides, in a one-pot procedure without isolation of the methylthio intermediate, as demonstrated by the synthesis of 2-amino-6-ethoxypyrimidine-4-carbal-dehyde 679 from the protected aldehydes 676 and 678 <2003T2631>. 

If ligation through a chosen side chain is desired, it can be introduced in the form of Ne-seryl-Lys, particularly if the fragment in question is to be made by total chemical synthesis. The periodate oxidation of a Ser that has a free N-terminus is so simple and satisfactory that we regard such a residue simply as a protected aldehyde. 

Although Z-alkene isosteres have been obtained from Wittig alkenation reactions of a-amino aldehydes using triphenyl[3-(trimethylsilyl)prop-2-ynylidene]phosphorane (Section 10.5.2.1.2.1), this stereoisomer was always obtained in minor amounts. Z-Selective alkena-tions were obtained using ylides containing dioxolane-protected aldehydes 42 or orthoester-protected carboxylic acid functions. 58 No experimental data were published, however. 

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