Methoxymethylene ether

In the original Merck procedure commercial 30% formalin was used as the source of formaldehyde, and in the case of cortisol (1) it was observed that the 1 lyS-hydroxyl group reacted in part to give the 1 l 8-methoxymethylene ether (2), ascribable to the presence of methanol in the formalin. Syntex workers circumvented this side... 

The Wittig reaction can be applied to various functionalized ylides.246 Methoxymethylene and phenoxymethylene ylides lead to vinyl ethers, which can be hydrolyzed to aldehydes.247... 

The phosphorus ylide may be obtained from a wide range of different halides, and thus ketones may be converted into a range of unsaturated compounds. A useful reaction with the methoxymethylene Wittig reagent leads, via the acid-labile enol ether, to an aldehyde (Scheme 3.48). 

In this section, the formation and cleavage of eight protecting groups for alcohols and phenols are presented acetate acetonides for diols benzyl ether para-methoxybenzyl (PMB) ether methyl ether methoxymethylene (MOM) ether ferf-butyldiphenylsilyl (TBDPS) silyl ether and tetrahydropyran (THP). 

The methoxymethylene (MOM) ether belongs to a class of substituted ether protecting groups. Unlike methyl ether, however, the MOM ether is actually an acetal, which is... 

Because the methoxymethylene group attached at C-4 normally is not involved in the fragmentation of these alkaloids, the mass spectra of various carbinolamine ethers were utilized to determine the nature of the C-4 substituents. From the published mass spectral data, no definite conclusion about the nature of C-4 groups can be predicted. 

Another high-yield synthesis of furoquinoline alkaloids, devised by Narasimhan and Mali (197), also involves the preparation of aldehydes 247 and their cyclization with polyphosphoric acid, and is illustrated in Scheme 21 for dictamnine. In this route, treatment of lithiated 2,4-dimethoxyquinolines with W-methylformanilide gave 3-formylquinolines 260. Wittig reactions with methoxymethylene triphenylphosphonium chloride and /ert-butoxide led to a mixture of cis- and frans-enol ethers, which were hydrolyzed to the 2-quinolone aldehydes. Dictamnine, evoli-trine, pteleine, and y-fagarine were synthesized by this method. 

The synthetic utility of carbonyl olefination reactions can be expanded beyond alkene synthesis through the use of functionalized ylides and functionalized phosphonate carbanions. Thus, methoxymethylene and phenoxymethylene ylides lead to vinyl ethers which can be readily hydrolyzed to aldehydes. 

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