Provided is a hydroxyl-protected alcohol of the formula R--O--Pg, wherein Pg is a protecting group of the formula: ##STR00001## wherein Y, Z, W, R.sup.1, R.sup.1a, R.sup.2, R.sup.2a, R.sup.3, R.sup.3a, R.sup.4, R.sup.4a, a, b, c, d, e and f are defined herein and R is a nucleosidyl group, an oligonucleotidyl group with 2 to about 300 nucleosides, or an oligomer with 2 to about 300 nucleosides. Also provided is a deprotection method, which includes heating the hydroxyl-protected alcohol at a temperature effective to cleave thermally the hydroxyl-protecting group therefrom.