Protection with methoxymethyl group

Treatment of 8-azidomethylperhydropyrido[l,2-c]pyrimidin-l-one 157 with methyl triflate and catalytic hydrogenation of the azide group led to the formation of tricyclic guanidine derivative 158 (01JA8851). Hydroxy group of 149 was protected with methoxymethyl chloride, and the p-methoxybenzyl protecting group (PMB) was eliminated by treatment with DDQ. 

The methoxymethyl ether protecting groups of 33 were then cleaved using triphenylphosphine and carbon tetrabromide. The resulting hydroquinone function was oxidized by palladium on carbon under an atmosphere of air to afford the quinone 52 (70 %). A two-step procedure was implemented to install the diazo function. First, the ketone function of 52 was condensed with N,N -bis( tert-butyldimethylsilyl)hydrazine in the presence of scandium triflate, which formed the Af-tert-butyldimethylsilyl hydrazone 53. The hydrazone (53) was then oxidized using difluoroiodobenzene to afford kinamycin C (3) in 35 % yield. 

Hydroxyl groups protected as acetonides or as silyl, tetrahydropyranyl, benzyl, or methoxymethyl ethers are stable to these conditions. Yields with KMn04 are higher than those obtained with KMn04 and dicyclohexyl- 18-crown-6, Bu4NMn04, or NaMn04H20. ... 

A straightforward synthesis (Scheme 3) of a furocoumarin-thymidine furan-side adduct was developed <1997JOC2630>. The methoxymethyl (MOM)-protecting group in 33 was removed in 91% yield with ethanolic HCl, and the resulting phenol 34 was condensed with dimethylacetamide dimethyl acetal in the presence of 4 A... 

A methoxymethyl (MOM) protecting group at N-3 was chosen based on its successful use in the total synthesis of nucleoside Q.31 Our previous experience with the total synthesis of rigidin vide supra) suggested BOM protection for the N-1 position and a 2,4-dimethoxybenzyl (DMB)... 

Achiral allylic boranes and chiral aldehydes. The reaction of pinacol-derived al-lylboronate 175 with a number of chiral aldehydes proceeds in only modest selectivity (Scheme 10-73) [120], Almost all of the aldehydes examined demonstrate a weak preference for the syn or Cram product. Almost no change in selectivity was observed when the protecting group on the alcohol is changed from a /-butyl-siloxy to a methoxymethyl group. 

Removal of the methoxymethyl groups from 43 with HCl, followed by protection of the secondary amine with benzyl chloroformate afforded the carbamate 9. Selective silylation of the 4-hydroxy group of 9 by treatment with 1.2 equiv of tert-butyldimethylsilyl chloride and 2.4 equiv of imidazole in DMF at room temperature for 1 h afforded the corresponding silyl ether as a single isomer in 80% yield that was subjected to acetylation at the C-3 hydroxyl group to afford the carbamate 11, which upon removal of the Cbz and TBDMS groups furnished 1. 

Methoxymethyl ethers protection of the hydroxyl groups was carried out by reaction of 89 with dimethoxymethane in the presence of P2O5. Deprotection of the W-benzyl group from 90 by hydrogenation in the presence... 

A reported diastereoselective synthesis of precursor A of vitamin D3 involved the use of 2-methylcyclopent-2-enone as starting material. The Mukaiyama-Michael conjugate addition of ketene acetal 269 in the presence of trityl hexachloroaniimonate afforded the adduct 270. The lateral chain was introduced, according the procedure of Tsuji, by the treatment of crude 270 with allyl carbonate and palladium dibenzylideneacetone " (Scheme 63). The expected product 271 was obtained in 63% yield from 269. Reduction of 271 with LAH afforded a mixture of diols that was selectively tosylated at the primary hydroxy group. The secondary hydroxy group was protected with the methoxymethyl group and further functional modifications afforded the lactone 272. The reaction of lithium dimethyl methylphosphonate with the lactone 272 completed the synthesis of the AB-des-cholestane derivative 273. 

In order to achieve controlled polymerization from die bdk ligand, an ethanol moiety is introduced to the phenol site to provide a primary alcohol site, and a less sterically crowded enviromnent for initiation (Figure 4). The alcohol requires protection in order to prevent deprotonation under die basic reaction conditions required for the ester and ketone condensation. A number of protecting groups were screened for this purpose, and one promising strategy involves methoxymethyl (MOM) protection. The formation of the MOM ether proceeds in nearly quantitative yield. After the condensation, the MOM group can be removed with aqueous HCl in THF. 

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