Wright type delay differential equations with negative Schwarzian

We prove that the well-known 3/2 stability condition established for the Wright equation (WE) still holds if the nonlinearity $p(\exp (-x)-1)$ in WE is replaced by a decreasing or unimodal smooth function f with $f^{\mathrm{\prime }}(0)<0$ satisfying the standard negative feedback and below boundedness conditions and having everywhere negative Schwarz derivative.