You can use "so as to" at the beginning or in the middle of a sentence.

It's correct to start a sentence with "so as to". For example:

So as to reduce business expenses, the company has cut production costs.

"So as to" is a compound preposition that has an infinitive as its object. When starting a sentence with it, be aware of:

1. Commas. Use a comma after an introductory phrase starting with "so as to" (learn more about how to use commas with "so as to").

   So as to learn a new language effectively, focus on common grammatical patterns.

   So as to learn a new language effectively focus on common grammatical patterns.

2. Emphasis. This particular construction can be used for emphasis. Overusing it, though, can be problematic from a style perspective.

   So as to solve a hard problem, you need to be able to think differently. (It shows emphasis.)

   You need to be able to think differently so as to solve a hard problem. (a more neutral version)

3. The negative ("so as not to") may be unnecessary at the beginning of a sentence. For example, in many situations you can change a negative statement into an affirmative sentence by using verbs such as "protect", "avoid", "prevent", "decrease" (instead of "increase"), etc.

   So as not to waste energy, optimize the use of refrigeration.

   So as to reduce energy waste, optimize the use of refrigeration.

Be also aware that you can replace "so as to" by "in order to".

In order to reduce energy waste, optimize the use of refrigeration.

"So as to" vs. "In order to"

We'll add here that you can use "to" instead of "so as to" in many situations. ¿What's the difference between "to" and "so as to"? "So as to" is much more formal.