Process for producing ester compound

A nitroacetal compound represented by Formula (4)

• wherein R1 and R2 each independently represent a hydrogen atom, an optionally substituted alkyl group, an optionally substituted alkoxy group, an optionally substituted alkenyl group, an optionally substituted alkenyloxy group, an optionally substituted cycloalkyl group, an optionally substituted cycloalkoxy group, an optionally substituted aryl group, an optionally substituted heteroaryl group, a halogen atom, an optionally substituted alkoxycarbonyl group, or an optionally substituted amino group, R4s each represent an alkyl group or the two R4s are combined together to represent an alkylene group, and n represents 1 or 2.

An aminoacetal compound represented by Formula (5)

• wherein R1 and R2 each independently represent a hydrogen atom, an optionally substituted alkyl group, an optionally substituted alkoxy group, an optionally substituted alkenyl group, an optionally substituted alkenyloxy group, an optionally substituted cycloalkyl group, an optionally substituted cycloalkoxy group, an optionally substituted aryl group, an optionally substituted heteroaryl group, a halogen atom, an optionally substituted alkoxycarbonyl group, or an optionally substituted amino group, R4s each represent an alkyl group or the two R4s are combined together to represent an alkylene group, and n represents 1 or 2,
• or a salt thereof.

A protected aminoacetal compound represented by Formula (6)

• wherein R1 and R2 each independently represent a hydrogen atom, an optionally substituted alkyl group, an optionally substituted alkoxy group, an optionally substituted alkenyl group, an optionally substituted alkenyloxy group, an optionally substituted cycloalkyl group, an optionally substituted cycloalkoxy group, an optionally substituted aryl group, an optionally substituted heteroaryl group, a halogen atom, an optionally substituted alkoxycarbonyl group, or an optionally substituted amino group, R4s each represent an alkyl group or the two R4s are combined together to represent an alkylene group, R5 represents a protecting group of an amino group, the protecting group being an optionally substituted alkyloxycarbonyl group, an optionally substituted aryloxycarbonyl group, or an optionally substituted aralkyl group, and n represents 1 or 2, or a salt thereof.

A nitrile compound represented by Formula (7)

• wherein R1 and R2 each independently represent a hydrogen atom, an optionally substituted alkyl group, an optionally substituted alkoxy group, an optionally substituted alkenyl group, an optionally substituted alkenyloxy group, an optionally substituted cycloalkyl group, an optionally substituted cycloalkoxy group, an optionally substituted aryl group, an optionally substituted heteroaryl group, a halogen atom, an optionally substituted alkoxycarbonyl group, or an optionally substituted amino group, R4s each represent an alkyl group or the two R4s are combined together to represent an alkylene group, R5 represents a protecting group of an amino group, the protecting group being an optionally substituted alkyloxycarbonyl group, an optionally substituted aryloxycarbonyl group, or an optionally substituted aralkyl group, and n represents 1 or 2, or a salt thereof.

A protected amino acid compound represented by Formula (8)

• wherein R1 and R2 each independently represent a hydrogen atom, an optionally substituted alkyl group, an optionally substituted alkoxy group, an optionally substituted alkenyl group, an optionally substituted alkenyloxy group, an optionally substituted cycloalkyl group, an optionally substituted cycloalkoxy group, an optionally substituted aryl group, an optionally substituted heteroaryl group, a halogen atom, an optionally substituted alkoxycarbonyl group, or an optionally substituted amino group, R5 represents a protecting group of an amino group, the protecting group being an optionally substituted alkyloxycarbonyl group, an optionally substituted aryloxycarbonyl group, or an optionally substituted aralkyl group, and n represents 1 or 2, or a salt thereof.

A protected aminoaldehyde compound represented by Formula (6a)

• wherein R1 and R2 each independently represent a hydrogen atom, an optionally substituted alkyl group, an optionally substituted alkoxy group, an optionally substituted alkenyl group, an optionally substituted alkenyloxy group, an optionally substituted cycloalkyl group, an optionally substituted cycloalkoxy group, an optionally substituted aryl group, an optionally substituted heteroaryl group, a halogen atom, an optionally substituted alkoxycarbonyl group, or an optionally substituted amino group, R5 represents a protecting group of an amino group, the protecting group being an optionally substituted alkyloxycarbonyl group, an optionally substituted aryloxycarbonyl group, or an optionally substituted aralkyl group, and n represents 1 or 2, or a salt thereof.

A protected aminoalcohol compound represented by Formula (6b)

• wherein R1 and R2 each independently represent a hydrogen atom, an optionally substituted alkyl group, an optionally substituted alkoxy group, an optionally substituted alkenyl group, an optionally substituted alkenyloxy group, an optionally substituted cycloalkyl group, an optionally substituted cycloalkoxy group, an optionally substituted aryl group, an optionally substituted heteroaryl group, a halogen atom, an optionally substituted alkoxycarbonyl group, or an optionally substituted amino group, R5 represents a protecting group of an amino group, the protecting group being an optionally substituted alkyloxycarbonyl group, an optionally substituted aryloxycarbonyl group, or an optionally substituted aralkyl group, and n represents 1 or 2, or a salt thereof.