Casually jilted outside entrance to synagogue, Dutch style (2,5)
I believe the answer is:
de stijl
'dutch style' is the definition.
(Dutch art style)
'casually jilted outside entrance to synagogue' is the wordplay.
'casually' indicates anagramming the letters (I've seen this in other clues).
'outside' means one lot of letters goes inside another.
'entrance to' indicates taking the first letters.
The initial letter of 'synagogue' is 's'.
'jilted' with letters rearranged gives 'detijl'.
'detijl' placed around 's' is 'DE STIJL'.
(Other definitions for de stijl that I've seen before include "Dutch modern art movement" , "group of Mondrian's" .)