Propargyl ethers, facile synthesis

The facility of these reactions was attributed to the favorable geometry of the allenyl ether for intramolecular Diels-Alder reactions, compared with that of the propargyl ether. These methodologies were used in a new synthesis of a naturally occurring furocoumarin, psoralen 308, which is of interest because of its unique photoreactions with DNA and its utility as a phototherapeutic agent. 

Bromoetherification of alkenes can be achieved using NBS in the desired alcohol as the solvent. The reaction of 1,3-dichloropro-pene with NBS in methanol yields an a-bromo dimethyl acetal in the first step in a convenient synthesis of cyclopropenone. Using propargyl alcohol the reaction depicted in eq 22 has been extended to an annulation method for the synthesis of a-methy-lene-y-butyrolactones. Intramolecular bromoetherification and bromoamination reactions are generally very facile (eq 23). In natural products synthesis, bromoetherification has been used for the synthesis of cyclic ethers (by subsequent debromination, see... 

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