One business transaction left Yemeni leader in a perfect situation (7)
I believe the answer is:
ideally
'in a perfect situation' is the definition.
(I've seen this before)
'one business transaction left yemeni leader' is the wordplay.
'one' becomes 'i' (Roman numeral).
'business transaction' becomes 'deal' (I've seen this before).
'leader' suggests taking the first letters.
The first letters of 'left yemeni' is 'ly'.
'i'+'deal'+'ly'='IDEALLY'
(Other definitions for ideally that I've seen before include "In the best of all possible worlds" , "In a perfect world, the best possible situation" , "In perfect circumstances" , "in optimal way" , "for best results" .)