Allylic glycolates, rearrangements

Claisen rearrangement of glycolates. Two laboratories 2 have reported that allylic glycolate esters undergo Claisen-Ireland rearrangement (6, 276-277) with useful diastereoselectivity. This rearrangement was used in a synthesis of 1, the aggregation pheromone of the European elm bark beetle.1... 

A Special feature of the boron or tin triflate mediated Claisen rearrangement of allylic glycolates or related substrates is that they avoid strongly basic conditions and thus eliminate the need to generate silyl ketene acetal intermediates in which C-silylation is a potential problem497. 

A novel synthesis of (+)-avenaciolide (341) centres on the stereospecific elaboration of the anti-ester (339) by an enolate Claisen rearrangement of the corresponding ( Z)-allylic glycolate and a highly stereoselective selenolactonization of the derived... 

In 1983, Burke et al. reported the enoHzation of an allylic glycolate in the presence of the unprotected cyclopentenone (Scheme 4.45) [48]. Only sHghdy over one equivalent of base was necessary to effect the enolization at -100 °C, indicating that concomitant enohzation of the enone was not competitive. The stereochemical outcome of the rearrangement of the Z-silyl ketene acetal is consistent with the expected chair-like transition state. 

Treatment of 2,4,6-triphenylpyrylium perchlorate with 3-benzo[i>]-thienylmethylmagnesium bromide affords the 4//-pyran (155),460 which undergoes allylic rearrangement in diethylene glycol in the presence of sodium to give the 2//-pyran (156).461 Under the same reaction conditions 156 is further converted by an intramolecular aldol condensation into 3-(2,4,6-triphenylphenyl)benzo[6]thiophene. 

Polyether Polyols. Polyether polyols are addition products derived from cyclic ethers (Table 4). The alkylene oxide polymerization is usually initiated by alkali hydroxides, especially potassium hydroxide. In the base-catalyzed polymerization of propylene oxide, some rearrangement occurs to give allyl alcohol. Further reaction of allyl alcohol with propylene oxide produces a monofunctional alcohol. Therefore, polyether polyols derived from propylene oxide are not truly difunctional. By using zinc hexacyano cobaltate as catalyst, a more difunctional polyol is obtained (20). Olin has introduced the difunctional polyether polyols under the trade name POLY-L. Trichlorobutylene oxide-derived polyether polyols are useful as reactive fire retardants. Poly(tetramethylene glycol) (PTMG) is produced in the acid-catalyzed homopolymerization of tetrahydrofuran. Copolymers derived from tetrahydrofiiran and ethylene oxide are also produced. 

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