Tricyclo-DNA nucleoside precursors and processes for preparing the same

A method of preparing a tc-DNA nucleoside precursor of any one of Formulas I-III:

• the method comprising the steps of:
• a. preparing a carbene precursor at a carbene preparation temperature, wherein the step of preparing the carbene precursor comprises combining a first Lewis acid and R7I2 in a solvent, wherein R7 is selected from the croup consisting of CH2, CH—C1-6alkyl, CH—C2-6alkenyl, CH—C2-6alkynyl, substituted CH—C1-6alkyl, substituted CH—C2-6alkenyl, substituted CH—C2-6alkynyl, and CH-(CH2)n—C(O)-R8, wherein n is 0 to 6 and wherein R8 is selected from the croup consisting of OH, NH2, O-C1-32alkyl and NH-C1-32alkyl;
• b. mixing the carbene precursor with a compound of Formula X, Formula XI, or Formula XII:
• at a cyclopropanation temperature;
• and
• c. adding a catalytic amount of a second Lewis acid to the mixture;
• wherein X and Y are each alkoxy;
• T1, T2, T3 and T4 are each OR5, where each R5 is H or a hydroxyl protecting group;
• q5, q6, and q7, and q8 are each independently selected from the group consisting of hydrogen, halogen, C1-6alkyl, C2-6alkenyl, C2-6alkynyl, substituted C1-6alkyl, substituted C2-6alkenyl, substituted C2-6alkynyl, and —(CH2)n—C(O)-R6, wherein n is 0 to 6 and wherein R6 is selected from the group consisting of OH, NH2, O-C1-32alkyl and NH-C1-32alkyl;
• q8 is selected from the group consisting of hydrogen, halogen, C1-3alkyl, C2-3alkenyl, C2-3alkynyl, substituted C1-3alkyl, substituted C2-3alkenyl, substituted C2-3alkynyl, and —(CH2)n—C(O)—R6, wherein n is 0 to 2 and wherein R6 is selected from the group consisting of OH, NH2, O-C1-3alkyl and NH-C1-3alkyl;
• and
• z3 and z4 are each independently selected from the group consisting of hydrogen, C1-6alkyl, C1-6alkoxyl, O-C2-6alkenyl, O-C2-6alkynyl, substituted C1-6alkyl, substituted C1-6alkoxy, substituted O-C2-6alkenyl, and substituted O-C2-6alkynyl halogen.