Novel pyran derivative, its preparation method, liquid crystal composition and liquid crystal display device comprising the same

A method for preparing a pyran derivative comprising the steps of:

• cyclizing a compound of the following Chemical Formula II to form a compound of the following Chemical Formula III;
• and
• forming a pyran derivative of the following Chemical Formula I from the compound of the Chemical Formula III:
• wherein,
• R is H, C1 ˜C15 alkyl, C2˜C15 alkenyl group or R1O—;
• R1 is H, C1 ˜C15 alkyl or C2˜C15 alkenyl group;
• ring C is
• ring A and ring B are independently
• Y1 is H, F, Cl, CN or CF3;
• Y2 is F, Cl, CN or CF3;
• a1 and a2 are independently O or N;
• Z1, Z2 and Z3 are independently —(CH2)n— (n is 0 or 2), —C≡C—, —C(═O)O—, —OC(═O)—, —CF2O—, —OCF2—, —OC(═O)O—, —CH2O—, —CH2C(═O)—, —OCH2— or —C(═O)CH2—;
• X is Cl, F, CF3, OCF3, OCHF2, CHF2, CH2F, OCF2CHF2 or OCF2CHFCH3;
• L1 to L8 are independently H or F;
• and,
• j, k, l and m are 0, 1 or 2.