Clarification of IUPAC name
Subsection P-44.4.1.10.1 in Nomenclature of Organic Chemistry – IUPAC Recommendations and Preferred Names 2013 (Blue Book) reads


  For the endings 'ene' and 'yne' lower locants are assigned first to the endings as a set without regard to type and then to 'ene' endings.


Since the locant set "1,3" is lower than the locant set "2,4" (see here for a discussion of what that means), the appropriate choice of locants for the above compound leads to the name pent-3-en-1-yne.





As an aside, the configuration of the double bond, if unspecified, should be labelled with the symbol Ξ (P-91.2.1.2.1).


  When the configuration is not known or must remain unspecified for lack of configurational homogeneity, the italicized symbol 'ξ' or 'Ξ' is used, preceded by the required locant. The symbol 'ξ' (small Greek letter 'xi') replaces noncapitalized CIP stereodescriptors such as 'r', 's', 'm', 'p'. The symbol 'Ξ' (capital Greek letter 'xi') replaces capitalized CIP stereodescriptors such as 'R', 'S', 'M', 'P', and nonCIP stereodescriptors 'E', 'Z', 'seqCis', and 'seqTrans'.


The preferred IUPAC name (PIN) for the compound with unspecified double bond geometry is therefore (3​Ξ)-pent-3-en-1-yne.

Of course, if the configuration is specified, then the (E)/(Z) labels should be used instead.