Carbonates diol protection

Removal of the unsaturated side-chain appendage from C-8 in 22 provides diol lactone 23 and allylic bromide 24 as potential precursors. In the synthetic direction, a diastereoselective alkylation of a hydroxyl-protected lactone enolate derived from 23 with allylic bromide 24 could accomplish the assembly of 22, an intermediate that possesses all of the carbon atoms of PGF2o- It was anticipated that preexisting asymmetry in the lactone enolate would induce the... 

The C2-symmetric epoxide 23 (Scheme 7) reacts smoothly with carbon nucleophiles. For example, treatment of 23 with lithium dimethylcuprate proceeds with inversion of configuration, resulting in the formation of alcohol 28. An important consequence of the C2 symmetry of 23 is that the attack of the organometallic reagent upon either one of the two epoxide carbons produces the same product. After simultaneous hydrogenolysis of the two benzyl ethers in 28, protection of the 1,2-diol as an acetonide ring can be easily achieved by the use of 2,2-dimethoxypropane and camphor-sulfonic acid (CSA). It is necessary to briefly expose the crude product from the latter reaction to methanol and CSA so that the mixed acyclic ketal can be cleaved (see 29—>30). Oxidation of alcohol 30 with pyridinium chlorochromate (PCC) provides alde-... 

A cyclic carbonate was utilized as a protecting group for the cw-diol system in butane-1,2,4-triol ... 

The five-membered 1,2-cyclic carbonate was isolated as the only product (regio-selective protection of the vicinal diol system).[255J Analogous formation of a cyclic carbonate containing a secondary hydroxy group is described in reference [256]. 

Concomitant protection of the amino group and the cis-hydroxyl group of the diol 342 was realized by treatment with formaldehyde to afford the oxazolidine 345, oxidation of which with silver carbonate on Celite gave the... 

When 1,2-diols are subjected to the same reaction conditions required for the formation of sulphonic esters, oxiranes are produced [27]. Presumably, the mono ester is initially formed and, under the basic conditions, intramolecular elimination occurs to produce the oxirane. Partial hydrolysis and ring-closure of a,p-di(tosyloxy) compounds under basic phase-transfer catalytic conditions provides a convenient route to carbohydrate oxiranes [e.g. 28, 29]. Oxiranes have been produced by an analogous method via carbonate esters from partially protected carbohydrates [30],... 

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