<ItemGroup>
    <File Include="One.cs" />
    <File Include="Two.cs" />
</ItemGroup>

<Copy SourceFiles="@(File)"
      DestinationFiles="@(File -> '%Filename''.out')"
      />

<ItemGroup>
    <OutputFile Include="@(File->'%Filename''.out')" />
</ItemGroup>

<ItemGroup>
    <OutputFile Include="@(File->'%(Filename)''.out')" />
</ItemGroup>

<ItemGroup>
  <OutputFile Include="%(File.Filename).out" />
</ItemGroup>