A compound represented by general formula (1) or a Bronsted acid salt thereof:
- wherein R12, R13, R14, R15, R16, R17, R18 and R19 each independently represent a hydrogen atom, an optionally substituted alkyl group, an optionally substituted cycloalkyl group, an optionally substituted aryl group, or an optionally substituted aralkyl group,
- U represents a group represented by the following general formula (2A) or (2B):
- wherein the dotted lines each independently represent a single bond or a double bond, and the solid line intersected with the wavy line represents a binding hand to the adjacent atom,
- Q1 and Q2 each independently represent an optionally substituted alkylene group, an optionally substituted aralkylene group or an optionally substituted arylene group,
- R20 represents a hydrogen atom, an alkyl group, a cycloalkyl group, an optionally substituted alkenyl group, an optionally substituted alkynyl group, an optionally substituted aryl group, an optionally substituted heteroaryl group, or an optionally substituted aralkyl group,
- Y1, Y2, Y3 and Y4 each independently represent a carbon atom, a nitrogen atom, an oxygen atom or a sulfur atom, provided that at least two of Y1, Y2, Y3 and Y4 are carbon atoms,
- R21, R22 and R23 each independently represent a hydrogen atom, an alkyl group, a cycloalkyl group, an optionally substituted alkenyl group, an optionally substituted alkynyl group, an optionally substituted aryl group, an optionally substituted aryloxy group, an optionally substituted heteroaryl group, an optionally substituted aralkyl group, an optionally substituted alkoxy group, an optionally substituted aralkyloxy group, an optionally substituted amino group or a halogeno group, or R21 and R22, or R22 and R23 may be joined together to form an optionally substituted aromatic ring or an optionally substituted heteroaromatic ring, and
- k is 1 or 2,
- G and G′ each independently represent a hydrogen atom, or at least one of G and G′ represents a group represented by the following general formula (GP):
- wherein the dotted line represents a coordinate bond, and the solid line intersected with the wavy line represents a binding hand to the adjacent atom,
- L represents a lone electron pair or BH3, and
- R1 and R2 each independently represent an optionally substituted alkyl group, an optionally substituted cycloalkyl group, an optionally substituted alkenyl group, an optionally substituted alkynyl group, an optionally substituted aryl group, an optionally substituted aryloxy group, an optionally substituted heteroaryl group, an optionally substituted aralkyl group, an optionally substituted alkoxy group, an optionally substituted aralkyloxy group or an optionally substituted amino group, or R1 and R2 may be joined together to form an optionally substituted ring together with their adjacent phosphorus atom, or
- a group represented by the following general formula (GS):
- wherein the solid line intersected with the wavy line represents a binding hand to the adjacent atom, and
- R3 represents an optionally substituted alkyl group, an optionally substituted cycloalkyl group, an optionally substituted alkenyl group, an optionally substituted alkynyl group, an optionally substituted aryl group, an optionally substituted heteroaryl group, or an optionally substituted aralkyl group, or
- a group represented by the following general formula (GC-1) or (GC-2):
- wherein the double line represents a double bond, and the solid line intersected with the wavy line represents a binding hand to the adjacent atom,
- R4 and R9 each independently represent an optionally substituted alkyl group, an optionally substituted cycloalkyl group, an optionally substituted alkenyl group, an optionally substituted aryl group, an optionally substituted heteroaryl group, or an optionally substituted aralkyl group, and
- R5, R6, R7, R8, R10 and R11 each independently represent a hydrogen atom, an alkyl group, a cycloalkyl group, an optionally substituted alkenyl group, an optionally substituted aryl group, an optionally substituted heteroaryl group, an optionally substituted aralkyl group, an optionally substituted alkoxy group, an optionally substituted aryloxy group, an optionally substituted aralkyloxy group, or an optionally substituted amino group.