as 引导让步状语从句位于句首时,句子要倒装吗?

不用。比如：As the president has't come yet, we have to put off the meeting.

as 引导让步状语从句时,一般须用部分倒装.如：
Old as he is,he works like a young man.尽管他很老了,但他工作起来却像个年轻人.
Hard as he was working,he didn’t pass the exam.虽然他一直在努力学习,但他还是没有通过那次考试.
Try again as he will,he can’t succeed.尽管他还会再试一试,但是它不会成功.
as 引起的倒装分三种情况：表语、动词原形及状语的倒装.
1.表语的倒装
一般直接将表语提前到句首,若表语是带不定冠词a / an的单数可数名词,倒装后,不定冠词a / an须被省略.如：
Fine as he looks,he is ill with some serious diseases.
Child as he is,he knows much about the society.
2.原形动词的倒装
A.动词前面带有情态动词may,might,will,would,can,could等时,只将行为动词提到句首,而这些情态动词保留在原处.
B.若动词前面没有情态动词时,应在动词原来的位置加上助动词do的适当形式.
C.用于这一句型的动词一般是不及物动词,而不能是系动词或及物动词.如：
Swim as he can,he can’t swim so far.尽管他会游泳,但是他游不得那么远.
Run as he did,he didn’t run fast enough to catch the bus.虽然他跑,但是他跑得不够快而没有赶上汽车.
3.状语倒装
In the classroom as he stays,he doesn’t read his texts.尽管他呆在教室里,但他不读书.
Carefully as he worked,he made some mistakes.尽管他工作很细心,但还是除了一些差错.