Allenyl groups from dienes

The oxidative cyclization of allenyl alcohol 135 with a small excess of dimethyl-dioxirane leads to an intermediate diepoxide that rearranges to hydroxyfuranone 136 in 55% yield (Eq. 13.44) [52]. If the oxidative cyclization is conducted in the presence of 0.5 equiv. of toluenesulfonic acid, the major product is the furanone lacking the a-hydroxy group of 136. Hydroxyfuranones or pyranones are available from the same kinds of reactions of 5-methylhexa-3,4-dien-l-ol. 

Reaction of l-chloro-l,3,3-triphenylallene (19) with p-toluidine in the presence of silver triflate gave 2,3,4-triphenylbuta- l-aza-1,3-diene derivative 22a via a novel l, 2-phenyl shift not reported earlier in the solvolysis of allenyl chlorides. The reaction takes place via the formation of the allenyl cation, which is captured as its canonical propargyl cation, first affording the protonated amine 20 (R = Me). Proton transfer from the nitrogen to the acetylenic carbon is followed by migration of a phenyl group in the intermediate vinyl cation 21 (R = Me) to afford the iminium triflate 22a. The latter is hydrolyzed by aqueous sodium hydroxide to the azabutadiene 23 (equation 5). Similar reaction of 19 with aniline and silver triflate afforded the corresponding iminium triflate 22b. ... 

If the allenic Claisen substrate is derived from a secondary allenyl alcohol, e.g., 7, the relative configuration of the diastereomeric alcohol determines the geometries of the double bonds of the diene part, and the absolute configuration of the stereocenter at C-2 of the product depends on the absolute configuration of the substrate by 1,4-chirality transfer, provided the rearrangement takes place via a chairlike transition state. Chair transition state A, with the substitutuent R1 equatorial, seems to be preferred because of 1,3-diaxial interactions of R1 with the amide group in transition state B660. 

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