The Claisen rearrangement of propargyl vinyl ethers provides a new general method for the synthesis of allenic aldehydes. Boron trichloridecatalysed rearrangement of phenyl propargyl ethers gave only starting material and fission products. Cope rearrangement of a propargylvinylmalonic ester gave moderate yields of the allenic malonic ester together with fission products. The mechanistic implications of these reactions are discussed.AN investigation of the Claisen rearrangement of propargyl vinyl ethers and the Cope 2 rearrangement of propargylvinylmalonic esters was initiated in 1958 as part of our programme on stereospecific acetylene allene-rearrangements3We had established that propargyl vinyl and isobutenyl ethers gave allenic aldehydes on pyrolysis when a preliminary report of independent work by Jones, Loder, and Whiting 5 described the direct conversion of isobutyraldehyde dipropargyl and dibut-l-ynyl acetals to the corresponding allenic aldehydes without isolation of the ether; starting with optically active but-l-yn-3-01 of known absolute configuration the absolute configuration of the optically active allenic aldehyde was deduced by these authors postulating the ether as an intermediate. In view of this publication we decided to concentrate on the preparative aspect of the Claisen rearrangement .6 The following general procedure was developed. The propargylic ether was passed in a stream of nitrogen through an electrically heated glass tube (20 x 2 cm.) lightly packed with glass wool and the product was collected in a trap cooled to -60".Conversions were effected in the vapour phase at low concentrations and unstable products quickly removed from the reaction tube. In this way rearrangements could be carried out on a small scale (0.5-2.0 g.) at temperatures up to 400". Polysubstituted propargyl vinyl ethers were heated under reflux or prepared in situ from the a-chloroallyl ethers and rearranged without isolation at 120-150" to the allenic aldehydes (Table 1).

A new general method for the preparation of 1-chloroalkyl ethers and vinyl ethers is described. Boron trichloride with acetals or mixtures of alcohols and aldehydes gives excellent yields of 1-chloroalkyl ethers, which are converted into vinyl ethers with trimethylamine. A number of new prop-2-ynyl vinyl ethers have been prepared by this method.

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Allenic and acetylenic bromides were obtained under mild conditions in good yield from the corresponding alcohols by treating equimolar mixtures of alcohols and pyridine with the triphenylphosphite dibromide reagent.

The synthesis of hypoglycin A by way of the allenic intermediate, diethyl 1 -formylaminopenta-3,4-diene-l,1 -dicarboxylate, by Sirnrnons-Smith methylation, is described. Model experiments with ethyl buta-2.3-dienoate and diethyl allyl(formylamino)malonate gave ethyl methylenecyclopropanecarboxylate and, after hydrolysis and decarboxylation, 2-amino-3-cyclopropylpropionic acid. Degradation of hypoglycin A to (+)-3-methylpentanoic acid of known (S)-configuration establishes the configuration as (+)-(2s: 4s) -2-amino-4,5-methanohex-5-enoic acid.known to add to allenes at the more highly substituted double bond.13 The Simmons-Smith reaction is somewhat temperamental and requires an active zinc-copper couple and strictly anhydrous conditions for reasonable