Cayley-Dickson Construction from Commutative Associative Algebra is Associative

Theorem
Let $A = \left({A_F, \oplus}\right)$ be a $*$-algebra.

Let $A' = \left({A_F, \oplus'}\right)$ be constructed from $A$ using the Cayley-Dickson construction.

Then $A'$ is an associative algebra iff $A$ is both a commutative algebra and an associative algebra.

Proof
Let the conjugation operator on $A$ be $*$.

Let $\left({a, b}\right), \left({c, d}\right), \left({e, f}\right) \in A'$.

In order to streamline notation, let $\oplus$ and $\oplus$ both be denoted by product notation:
 * $a \oplus b =: a b$
 * $x \oplus' y =: x y$

The context will make it clear which is meant.

Suppose $A$ is commutative and associative.

Then:

Now suppose $A'$ is an associative algebra.

By picking apart the above series of equations, it is clear that $A$ has to be both commutative and associative in order to assure the associativity of $A'$.