Preparation formyl group removal from

Since benzyl groups can be removed from N,N-dibenzylcyclopropylamines by catalytic hydrogenation over palladium catalysts, primary cyclopropylamines are accessible by this methodology. Thus, the theoretically interesting tricyclopropylamine [106,107] could be prepared from benzylcyclopropylformamide by a sequence of reductive cydopropanation of the formyl group, hydrogenolytic debenzylation, N-formylation, and repeated reductive cydopropanation [106,107]. 

I, 4- and 3,4-Dihydroquinazolines are tautomeric but any attempts to prepare the former w ithout a 1-substituent have led to the latter. The greater stability to proto tropic change of 1,2-dihydronaphthalene over 1,4-dihydronaphthalene is also found in 3,4-dihydroquinazoline. Earlier claims to the preparation of l,4-dihydroquinazolines ° were erroneous and based on incomplete experimental data. The first 1,4-dihydroquinazoline was prepared as recently as 1961. 1-Methyl and l-benzyl-l,4-dihydroquinazolines were obtained from o-methylamino-and o-benzylamino-benzylamines (42) by formylation and ring closure. Attempts to remove the benzyl group gave 3,4-dihydroquinazoline. These 1,4-dihydro compounds are susceptible to oxidation, and attempts made to prepare 1,2-dimethyl-1,4-dihydroquinazoline from o-... 

Another technique is to block one of the a-positions by introduction of a removable substituent which prevents formation of the corresponding enolate. Selective alkylation can be performed after acylation with ethyl formate and transformation of the resulting formyl (or hydroxymethylene) substituent into a group that is stable to base, such as an enamine, an enol ether or an enol thioether. An example of this procedixre is shown in Scheme 1.16, in the preparation of 9-methyl-1-decalone from rra 5-1-decalone. Direct alkylation of this compound gives mainly the 2-alkyl derivative, whereas blocking the 2-position allows the formation of the required 9-alkyl-1-decalone (as a mixture of cis and trans isomers). 

A method has been described for the preparation of N-formyl-a-amino-acid t-butyl esters by formylation of the free base with a mixture of formic acid, DCC, and pyridine, thus overcoming the incompatibility of the t-butyl ester group with the usual acidic formylation conditions. The transfer hydrogenation technique has been recommended for the removal of N-benzyloxycarbonyl and benzyl ester groups from peptides. N-Acetyl-a-amino-acids are converted into the corresponding A-ethyl derivatives by reaction with Meerwein s reagent followed by reduction with sodium borohydride. ... 

Reductive deamination can be performed in reasonable yields via phenylimidoyl chlorides prepared from benzoyl derivatives of primary amines. Imidoyl chloride derivatives decompose on heating with TBTH and AIBN in xylene to yield alkanes (equation 80) . Primary amines can also be reductively deaminated in high yields via isocyanide derivatives. Formylation-dehydration transforms an amino group into an isocyanide quite routinely. Reductive removal of isocyanide can be performed with sodium naphthalenide in hydrocarbon solvents " or with TBTH in the presence of AIBN ". The TBTH reduction works equally well for primary, secondary and tertiary isocyanides and yields are good (equation 81) ". ... 

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