(R,R)-[N,N’-bis(3,5-di-tert-butylsalicylidene)-1,2-cyclohexanediamine] (Jacobsen’s Salen) as a chiral ligand for the chromium-catalyzed addition of 3-chloro-propenyl pivalate to aldehydes: a catalytic asymmetric entry to syn-alk-1-ene-3,4-diols