Piperidine derivative, liquid crystal composition and liquid crystal display device

A compound represented by formula (1):

• wherein, in formula (1),
• R1, R2, R3 and R4 are independently hydrogen or alkyl having 1 to 4 carbons, and R5 is hydrogen, hydroxy, oxy radical, alkyl having 1 to 10 carbons or alkoxy having 1 to 10 carbons;
• ring A1 is 1,4-cyclohexylene, 1,4-cyclohexenylene, 3,4-dihydro-2H-pyrane-2,5-diyl, 3,4-dihydro-2H-pyrane-3,6-diyl, 3,6-dihydro-2H-pyrane-2,5-diyl, tetrahydropyran-2,5-diyl, 1,3-dioxane-2,5-diyl, 1,2-phenylene, 1,3-phenylene, 1,4-phenylene, pyridine-2,5-diyl, pyrimidine-2,5-diyl, decahydronaphthalene-2,6-diyl, naphthalene-1,3-diyl, naphthalene-1,4-diyl, naphthalene-1,5-diyl, naphthalene-1,6-diyl, naphthalene-1,7-diyl, naphthalene-1,8-diyl, naphthalene-2,3-diyl, naphthalene-2,6-diyl or naphthalene-2,7-diyl, and in the rings, at least one hydrogen may be replaced by fluorine, chlorine, alkyl having 1 to 5 carbons, alkoxy having 1 to 5 carbons, or alkyl having 1 to 5 carbons in which at least one hydrogen is replaced by fluorine or chlorine, and one hydrogen may be replaced by a monovalent group represented by formula (P-1);
• wherein, in formula (P-1),
• R1, R2, R3 and R4 are independently hydrogen or alkyl having 1 to 4 carbons, and R5 is hydrogen, hydroxy, oxy radical, alkyl having 1 to 10 carbons or alkoxy having 1 to 10 carbons;
• Z2 is a single bond or alkylene having 1 to 10 carbons, and in the alkylene, at least one —CH2— may be replaced by —O—, —S—, —CO—, —COO— or —OCO—, and at least one —CH2—CH2— may be replaced by —CH═CH— or —C≡C—, and in the groups, at least one hydrogen may be replaced by fluorine or chlorine;
• and
• in formula (1),
• Z1 and Z2 are independently a single bond or alkylene having 1 to 10 carbons, and in the alkylene, at least one —CH2— may be replaced by —O—, —S—, —CO—, —COO— or —OCO—, and at least one —CH2—CH2— may be replaced by —CH═CH— or —C≡C—, and in the groups, at least one hydrogen may be replaced by fluorine or chlorine;
• and
• a is 0, 1, 2 or 3.