Compounds are provided having the following structure ##STR00001## and pharmaceutically acceptable salts thereof, ##STR00002## wherein R.sub.1, R.sub.2, R.sub.3, R.sub.4, U, V, W, Y, and n are as defined above, which compounds are HMG CoA reductase inhibitors and thus are active in inhibiting cholesterol biosynthesis, modulating blood serum lipids, for example, lowering LDL cholesterol and/or increasing HDL cholesterol, and treating hyperlipidemia, dyslipidemia, hypercholesterolemia, hypertriglyceridemia and atherosclerosis as well as Alzheimer's disease and osteoporosis and may be employed as hormone replacement therapy. A method for treating the above diseases employing the above compounds is also provided.