1.3- Dioxanes carbonyl group protection

Methylene derivatives, substituted, to protect carbonyl groups, 217 5-Methylene-l,3-dioxanes, to protect carbonyl groups, 186-187 S,S -Methylene dithioacetals, to protect S,Sr-dithiols, 305... 

Acetalizjation. The silylated diol is used in the protection of the carbonyl group (dehydration with 3A molecular sieves in dichloromethane). Carbonyl compounds are regenerated from the 5-trimethylsilyl-l,3-dioxanes by treatment with LiBF in refluxing THF. 

Like all acetalizations, 1,3-dioxane formation is reversible it finds wide appHcation for establishing the 1,3-dioxane moiety as protective group for carbonyl compounds, as well as for systems with a 1,3-diol structural element. 

Zinc-silver acetic acid Protection of carbonyl groups as 5,5-dibromo-l,3-dioxanes Reductive removal of tbe protective group... 

Aldehydes and ketones can be protected by conversion into the 5,5-dibromo-l,3-dioxan derivative. The diol required for the protection step, 2,2-dibromopropane-l, 3-diol, is readily prepared. The protecting group is stable to peracids and to hydride reducing agents, and the carbonyl group is readily regenerated by the action of a zinc-silver couple (Scheme 54). ... 

Diastereoselective U-4CR of chiral y-keto acid 10s with 6i and lx in 2,2,2-trifluoroethanol at room temperature provides y-lactam 205 in a 78% yield as a single diastereomer. The diastereoselectivity is believed to arise from the exclusive axial approach of small nucleophiles onto the carbonyl group of l,3-dioxan-4-ones [82]. Deprotection of the acetonide with catalytic amount of CSA in MeOH followed by protection of the diol to the corresponding diacetate and further treatment with catalytic amount of CSA in benzene provides the A-acylindole 206. The A-acylindole... 

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