MOM protection

Along with these well-defined complexes, other protocols have been developed to directly involve imidazolinm salts with Pd sonrces and form the active catalysts in situ. One of the most popnlar consists of the nse of carbene precursors such as IMes HCl or IPr HCl with PdCOAc) or PdCdba) and a base [40]. A mixture of SIPr HCl and PdCOAc) in a 1 1 ratio was nsed for the synthesis of resveratrol analogues (MOM protected MOM = methoxymethylether) through decarbonylative Mizoroki-Heck coupling [41] (Scheme 6.9). 

The dynamic kinetic resolution (DKR) of a-sulfur-substituted ketones such as 31 and 33 was investigated. When the MOM protected mercaptol ketone 31 was treated with the BINOL-LiAlH4 complex, a moderate diastereoselectivity of 5 1 favoring the desired anti isomer was observed. The major diastereomer had 70%... 

DKR via hydrosilylation was also investigated in the presence of the methyl-DuPhos rhodium complex. When MOM protected 31 was tested, a low yield of desired diasteromer was observed with modest 70% ee. On the other hand, the unprotected thiol-ketone 33 gave 89% ee of the desired anti-diastereomer in 40%... 

Decyl-5-methoxy-l-naphthol [Reduction of a Secondary Benzylic Alcohol to a Methylene Group with Concomitant Loss of a MOM Protecting Group].167... 

Hydrogenation of a series of /Z-isomeric mixtures of a-arylenamides with a MOM-protected /3-hydroxyl group catalyzed by a BICP-Rh complex or an Me-DuPhos complex leads to the formation of chiral /3-amino alcohol derivatives with excellent enantioselectivities.70b A 1,4-diphosphane 26 with a rigid 1,4-dioxane backbone is also very effective for this transformation (Equation (28)).76 DIOP -Rh72a and Me-DuPhos-Rh219 catalysts are also effective for this transformation. 

The system can also be made rigid by modification of the ketal portion, as illustrated by 14 and SK-Phos (15). These ligands provided high stereoselection for reductions of enamides and MOM-protected yS-hydroxy enamides [81]. 

One ligand system which was developed during the late 1990s, and has proven quite versatile for the reduction of a wide variety of unsaturations, including a-and /i-dehydroamino acids, arylenamides and MOM-protected /1-hydroxy en-amides, is the rigid BICP (26) [113-118],... 

The dihydropyran 88 served as the precursor for an oxocarbenium ion that was utilized as the acceptor for the intermolecular Hosomi-Sakurai reaction [53, 54]. Utilizing a second Hosomi-Sakurai reaction, pyran 88 was synthesized as outlined in Scheme 17 [53, 54]. Easy accessible MOM protect-... 

Scheme 17 Synthesis of the dihydropyran 88 from MOM-protected lactic aldehyde (91)...

The hydrogenation of a series of T/Z-isomeric mixtures of a-arylenamides containing a MOM-protected /9-hydroxyl group, using BICP-Rh and Me-DuPhos-Rh catalysts, affords the /9-amino alcohol derivatives with excellent enantioselectivity [41c]. A 1,4-di-phosphane, T-Phos, with a rigid 1,4-dioxane backbone is also a very effective Hgand for this transformation (Eq. 11) [45]. 

Hanaoka et al. reported a total synthesis of murrayaquinone A (107) based on an anionic [4+2] cycloaddition of the indole ester 864 with phenyl p-tiimethylsilylvinyl sulfone (865) (631). The reaction of the MOM-protected indole 864 with phenyl... 

Recently, Moody et al. reported a biomimetic synthesis of calothrixin B (378) by oxidation of Hibino s 6-formylindole[2,3-fl]carbazole 1555 (870). The key intermediate 6-formyl-indole[2,3-fl]carbazole was readily obtained in six steps from indigo (1458). Using Somei s procedure, indigo (1458) was transformed to the cis-chlorohydrin 1461 in three steps and 50% overall yield (see Scheme 5.247). The reduction of the chlorohydiin 1461 gave 5-hydroxy-indolo[2,3-fl]carbazole 1564, and subsequent Vilsmeier formylation delivered the desired 6-formyl-indole[2,3-fl]carba-zole 1565 in 45% yield. Reaction of hydroxy-indolocarbazole 1565 with an excess of chloromethyl methyl ether (MOMCI) afforded the tiis-MOM-protected compound 1555. Following Hibino s approach, the tris-MOM-protected indolocarbazole 1555... 

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... 

Alkylation of the highly versatile precursor A -MOM protected 3 with an enantioselectivity of 97-99 % ee, was again the key step of the first asymmetric synthesis of (—)-yohimbone47. The overall yield of the 11-step synthesis was 17%. 

An anion ol compound 11 reacts with the most reactive site in molecule 2. Which is this a) the MOM-protected hydroxy group b) the amide function or c) the aldeh>de ... 

Treatment with aqueous sulfuric acid cleaves the MOM protective group (which consists of an acetal structure) to give compound 48. 

When MOM protected y-allenol derivatives 188a and 188b were used as starting materials for the Auln-catalyzed cycloisomerization, the 5-exo mode was... 

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