We introduce the notion of crossed $n$-fold extensions of an algebra $B$ by a bimodule $M$ and prove that such extensions represent classes in the Hochschild cohomology of $B$ with coefficients in $M$. Moreover we consider this way characteristic classes of chain (resp. cochain) algebras in Hochschild cohomology.
Homology, Homotopy and Applications, Vol. 4(2), 2002, pp. 63-82