Allyl acetates cyclic ether synthesis

The 2-thiopyridone (78) is reportedly a superior reagent for the activated ester approach to macrolides, requiring no further activation s (e.g. with Ag ions). The selenolactonization procedure has been used for a reasonably efficient synthesis (ca. 50% yield) of the macrolide derivatives (80 n = 11 or 13) from the unsaturated acids (79) using the iV-phenylseleno-derivatives of suc-cinimide or phthalimide as carriers of the PhSe function. Trost and Verhoeven have reported more examples of the efficient preparation of medium-sized macrolides via Pd° 7r-complexes of allyl acetates (2,152). Further reports have appeared on the preparation of ten-membered keto-macrolides by oxidative ring cleavage of suitable cyclic ethers (c/. 3, 142, 143). 

Intramolecular allylation of oxocarbenium ions with allylsilanes is valuable for stereoselective synthesis of cyclic ethers. Allylsilanes (15a-c), bearing a hydroxy or trimethylsiloxy group, are convenient reagents for this cyclization. The (la)-promoted reactions of (15a-c) with carbonyls or acetals efficiently afford cyclic... 

Acyclic and cyclic allylic ethers and acetals react normally with dihalocarbenes at the C=C bond [e.g. 77, 85, 108,114,121,122], Carbene insertion into the C=C bond of allylic ketones, which can be complicated by competitive reaction by the carbonyl group, can also be effected via the initial formation of the acetal and has been used in the synthesis of cyclonona-3,4- and -4,5-dienones from cyclooctenones [125],... 

With a cyclic substrate, for example in which three or more atoms of the allyl vinyl ether are constrained in aring, then the boat-shaped transition state maybe favoured. Formation of the silyl ketene acetal from the lactone 295 and rearrangement on warming gave the carboxylic acid 296 (3.190). The reaction occurs via a boatshaped transition state and was used in a synthesis of the sesquiterpene widdrol. 

As shown in Scheme 32, when allylilc alcohols are allowed to react with vinyl ethers, the resulting a--bond in oxypalladation intermediate adds intramolecularly to the C=C bond of allylic moiety.f Subsequent (3-Pd—elimination leads to cyclic acetals. With this method, albeit stoichiometric in palladium(II), a unique approach to the synthesis of prostaglandins was attained by Larock and Lee as shown in Scheme 33.1 ... 

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