ortho esters

Compounds having the structure RC(OR')3 ( R'H), or the structure C(OR')4 ( R'H), e.g. HC(OCH3)3 trimethyl orthoformate, C(OCH3)4 tetramethyl orthocarbonate.
Source:
PAC, 1995, 67, 1307 (Glossary of class names of organic compounds and reactivity intermediates based on structure (IUPAC Recommendations 1995)) on page 1354