This invention is directed to compounds of the formula: wherein j is 0 or 1; k is 0 or 1; m is 0 or 1; n is 0 or 1; W is —O—; —S(═O)t—, where t is 0, 1, or 2; or —N(R3)—; where R3 is —H, —(C1-C3) alkyl, —OR12, phenyl, or benzyl; RC and RD have the same meaning as RA and RB, except that at least one of RC and RD must be —H; and the other variables are defined as set forth in the specification. The invention is also directed to pharmaceutical compositions comprising the above compounds and to methods of treating a subject suffering from a disease, disorder or condition mediated by the PDE4 isozyme, the method comprising administering a therapeutically effective amount of a compound as described above. The invention is particularly directed to methods of treating inflammatory, respiratory and allergic diseases and conditions, especially asthma; chronic obstructive pulmonary disease (COPD) including chronic bronchitis, emphysema, and bronchiectasis; chronic rhinitis; and chronic sinusitis.