Protecting moieties formyl

The oxazolidine system proved a good protecting group with which to mask the ethanolamine moiety in the a-formylation and a-benzoylation of 558, and it could also be used as an aldehyde donor in the rearrangement, based on the ring-chain tautomeric character of 559, under acidic conditions to yield 3-(2-hydroxyethyl)-substituted 1,3-oxazin-4-ones 560 (Scheme 106) <1996JOC3358>. 

A considerable number of electrophiles were used, and the dithiane route found great utility for the syntheses of simple monofunctional compounds as well as for polyfunctional molecules, for which the dithiane moiety affords an invaluable temporary protection of a future carbonyl group. Some experimental procedures published in Organic Syntheses — cyclobutanone [277] and 3-hydroxy-l-cyclohexene-l-carboxaldehyde [278] — are illustrative. A similar route to aldehydes [279] makes use of sym-trithiane as a formyl anion equivalent. 

Very recently, Node and co-workers improved the efficiency of this particular oxidative phenolic coupling in the context of a synthesis of (+)-galanthamine (51a) [50]. By using a trialkoxyarene as one of the aryl units, they were able to obtain yields of 56b of up to 90 % when the nitrogen was protected with a formyl group and the donor aryl s oxygen atoms were capped by benzyl moieties (Table 11). These authors were even able to isolate an interesting narwedine-type product 57a in low yield. 

N -benzyloxycarbonylt and N -Zert-butoxycarbonylt hydrazides. Other suggested protection schemes include masking of hydrazides by trityl,t l trifluoroacetylj formyl,trichloroethoxycarbonyl,t l and 4-picolyloxycarbonylt l moieties. 

A first approach described the use of catalyst 106a in the Michael reaction of a cyclic p-ketoester with acrolein (Scheme 5.28). ° The reaction proceeded satisfactorily, furnishing quantitatively the desired conjugate addition product in excellent enantioselectivity, requiring the in situ protection of the formyl moiety as the corresponding cyclic acetal derivative. However, the authors reported the need of a 9-fluorenyl ester Michael donor and the reaction was not studied further, with no data reported about the scope and limitations of the methodology. 

The formyl group in 13 was used to construct the piperidine A ring. Thus, once 13 was converted into an O-benzyl oxime, a hydroboration— oxidation reaction led to alcohol 14. Protection of the hydroxy group withp-methoxybenzyl chloride also caused the eHmination of the O-benzyl oxime moiety to give a nitrile, which was then reduced to the primary amine 15. 

Group. The A -[bis(trimethylsilyl)methyl] group also serves as an N-protecting group in amides and lactams. The N-[bis(trimethylsilyl)methyl] moiety is readily removed by oxidation using ceric(IV) ammonium nitrate (CAN) in aqueous acetonitrile. The initially formed A-formyl amide or lactam is readily deformylated by stirring in methanolic sodium or potassium carbonate (eqs 11, 12, and 13). ... 

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