A compound of Formula wherein Z is -O -; X is selected from the 5' end of a nucleoside, nucleoside analogue, oligonucleotide, or oligonucleotide analogue and Y is selected from the 3' end of a nucleoside, nucleoside analogue, oligonucleotide, or oligonucleotide analogue; -H, -OH, -SH, -O-PG, -S-PG, a linker, a monophosphate or diphosphate, or a label or quencher; or Y is selected from the 3' end of a nucleoside, nucleoside analogue, oligonucleotide, or oligonucleotide analogue and X is selected from the 5' end of a nucleoside, nucleoside analogue, oligonucleotide, or oligonucleotide analogue, -H, -OH, -SH, -O-PG, or -S-PG, a linker, a monophosphate or diphosphate, or a label or quencher; R 1 is selected from -NR 1A R 1B, -OR 3, -SR 3, -H, -S H, -S R 3, -S 2 H, -S 2 R 3, -S 2 NH 2, -S 2 NHR 3, -S 2 NR 3 2, -C 1 - 10 alkyl, -C 2 - 10 alkenyl, -C 2 - 10 alkynyl, -C 6 - 10 aryl, or -C 5-10 heteroaryl; R 2 is selected from -H, -NR 2A R 2B, -OR 3, -SR 3, halogen, -CN, -S H, -S R 3, -S 2 H, -S 2 R 3, -S 2 NH 2, -S 2 NHR 3, -S 2 NR 3 2, -C 1 - 10 alkyl, -C 2 - 10 alkenyl, -C 2 - 10 alkynyl, -C 6 - 10 aryl, or -C 5-10 heteroaryl; wherein each R 1A, R 1B, R 2A, and R 2B is independently selected from -H, -C 1 - 10 alkyl, -C 2 - 10 alkenyl, -C 2 - 10 alkynyl, -C 6 - 10 aryl, or -C 5-10 heteroaryl; optionally wherein R 1A and R 2A together form an alkylene or heteroalkylene chain of 2-4 atoms in length; optionally wherein R 1A and R 1B, together with the atom to which they are bound, form a 5-8 membered heterocycle; optionally wherein R 2A and R 2B, together with the atom to which they are bound, form a 5-8 membered heterocycle; R 3 is selected from -C 1 - 10 alkyl, -C 2 - 10 alkenyl, -C 2 - 10 alkynyl, -C 6 - 10 aryl, or -C 5-10 heteroaryl; wherein each alkyl, aryl, heteroaryl, alkylene or heteroalkylene is optionally substituted; wherein PG is a protecting group. Z is -O -; X is selected from the 5' end of a nucleoside, nucleoside analogue, oligonucleotide, or oligonucleotide analogue and Y is selected from the 3' end of a nucleoside, nucleoside analogue, oligonucleotide, or oligonucleotide analogue; -H, -OH, -SH, -O-PG, -S-PG, a linker, a monophosphate or diphosphate, or a label or quencher; or Y is selected from the 3' end of a nucleoside, nucleoside analogue, oligonucleotide, or oligonucleotide analogue and X is selected from the 5' end of a nucleoside, nucleoside analogue, oligonucleotide, or oligonucleotide analogue, -H, -OH, -SH, -O-PG, or -S-PG, a linker, a monophosphate or diphosphate, or a label or quencher; R 1 is selected from -NR 1A R 1B, -OR 3, -SR 3, -H, -S H, -S R 3, -S 2 H, -S 2 R 3, -S 2 NH 2, -S 2 NHR 3, -S 2 NR 3 2, -C 1 - 10 alkyl, -C 2 - 10 alkenyl, -C 2 - 10 alkynyl, -C 6 - 10 aryl, or -C 5-10 heteroaryl; R 2 is selected from -H, -NR 2A R 2B, -OR 3, -SR 3, halogen, -CN, -S H, -S R 3, -S 2 H, -S 2 R 3, -S 2 NH 2, -S 2 NHR 3, -S 2 NR 3 2, -C 1 - 10 alkyl, -C 2 - 10 alkenyl, -C 2 - 10 alkynyl, -C 6 - 10 aryl, or -C 5-10 heteroaryl; wherein each R 1A, R 1B, R 2A, and R 2B is independently selected from -H, -C 1 - 10 alkyl, -C 2 - 10 alkenyl, -C 2 - 10 alkynyl, -C 6 - 10 aryl, or -C 5-10 heteroaryl; optionally wherein R 1A and R 2A together form an alkylene or heteroalkylene chain of 2-4 atoms in length; optionally wherein R 1A and R 1B, together with the atom to which they are bound, form a 5-8 membered heterocycle; optionally wherein R 2A and R 2B, together with the atom to which they are bound, form a 5-8 membered heterocycle; R 3 is selected from -C 1 - 10 alkyl, -C 2 - 10 alkenyl, -C 2 - 10 alkynyl, -C 6 - 10 aryl, or -C 5-10 heteroaryl; wherein each alkyl, aryl, heteroaryl, alkylene or heteroalkylene is optionally substituted; wherein PG is a protecting group.