Synthesis of conjugated diene pheromones and related compounds
Methods for preparing conjugated dienes are described. An α,β-unsaturated E olefin intermediate may be prepared via cross-metathesis using a catalyst comprising a transition metal (e.g., ruthenium), a first carbene ligand (e.g., a substituted indenylidene) and an N-heterocyclic carbene ligand (e.g., an imidazolidinylidene). The catalyst further includes a phenylphosphine ligand, a tri(isopropoxy)phosphine ligand, a dimethylsulfoxide ligand, an acetonitrile ligand, or a pyridine ligand. Following the cross metathesis-step, the α,β-unsaturated aldehyde intermediate may be converted to the conjugated diene product via reaction with a phosphonium ylide. Products obtained via the methods of the disclosure include (7E,9Z)-dodeca-7,9-dien-1-yl acetate, a pheromone produced by Lobesia botrana (European grapevine moth), and other insect pheromones.
1. A method for preparing a conjugated diene according to Formula I:
the method comprising:
(i) forming a reaction mixture comprising:
an olefin according to Formula V:
a crotonaldehyde, and
a metathesis catalyst according to Formula VI:
(ii) maintaining the reaction mixture under conditions sufficient to form a metathesis product according to Formula III:
and
(iii) combining the metathesis product according to Formula III with a phosphonium ylide according to Formula II:
under conditions sufficient to form the conjugated diene according to Formula I, wherein:
R 1 is —OR 1a , —C(O)OR 1b , or —C(O)H,
R 1a is C 1-6 acyl or H,
R 1b is H or C 1-6 alkyl,
R 2 is C 3-12 alkyl or C 1-2 alkyl,
R 3a and R 3b are independently H or C 1-6 alkyl,
each R 5 is independently optionally substituted C 6 -C 10 aryl,
subscript x is an integer ranging from 6 to 12 or an integer ranging from 1 to 5,
R 6 and R 7 , together with the carbon atom to which they are attached, form a first carbene ligand,
R 8 and R 9 are independently anionic ligands,
L 1 is a N-heterocyclic carbene ligand, and
L 2 is a phenylphosphine ligand, a tri(isopropoxy)phosphine ligand, a dimethylsulfoxide ligand, an acetonitrile ligand, or a pyridine ligand.
2. The method of claim 1 , wherein the conjugated diene is an E,Z-diene.
3. The method claim 1 , wherein the first carbene ligand is optionally substituted indenylidene, optionally substituted alkylidene, optionally substituted benzylidene, optionally substituted vinylidene, or optionally substituted allenylidene.
4. The method of claim 1 , wherein R 6 and R 7 , together with the carbon atom to which they are attached, form 3-phenyl-1H-inden-1-ylidene, benzylidene, or 3-methylbut-2-en-1-ylidene.
5. The method of claim 4 , wherein R 6 and R 7 , together with the carbon atom to which they are attached, form 3-phenyl-1H-inden-1-ylidene.
6. The method of claim 1 , wherein L 1 is optionally substituted imidazolidin-2-ylidene.
7. The method of claim 1 , wherein the metathesis catalyst is selected from:
wherein “Ph” represents phenyl, “iPr” represents isopropyl, and DMSO represents dimethylsulfoxide.
8. The method of claim 1 , wherein the amount of the metathesis catalyst in the reaction mixture is less than 0.05 mol % with respect to the total amount of olefin according to Formula V and the crotonaldehyde.
9. The method of claim 1 , wherein the molar ratio of the crotonaldehyde to the olefin according to Formula V ranges from about 1.5:1 to about 3:1.
10. The method of claim 1 , wherein the metathesis product according to Formula III of step (ii) is not purified prior to step (iii).
11. The method of claim 1 , wherein the phosphonium ylide according to Formula II is formed by reacting a base with an alkylphosphonium halide according to Formula IIa
wherein X is halogen.
12. The method of claim 11 , wherein the base is potassium tert-butoxide.
13. The method of claim 1 , wherein the conjugated diene is selected from the group consisting of (7E,9Z)-dodeca-7,9-dien-1-yl acetate, (3E,5Z)-dodeca-3,5-dien-1-yl acetate, (3E,5Z)-dodeca-3,5-dien-1-yl acetate, (5E,7Z)-dodeca-5,7-dien-1-yl acetate, (8E,10Z)-dodeca-8,10-dien-1-yl acetate, (5E,7Z)-dodeca-5,7-dien-1-ol, (5E,7Z)-dodeca-5,7-dienal, (7E,9Z)-dodeca-7,9-dien-1-ol, (7E,9Z)-dodeca-7,9-dienal, (8E,10Z)-dodeca-8,10-dien-1-ol, (8E,10Z)-dodeca-8,10-dienal, (2E,4Z)-hepta-2,4-dien-1-ol, (2E,4Z)-hepta-2,4-dienal, (2E,4Z)-octa-2,4-dienal, (4E,6Z)-octa-4,6-dienoic acid, (2E,4Z)-deca-2,4-dienal, ethyl (2E,4Z)-deca-2,4-dienoate, (10E,12Z)-tetradeca-10,12-dien-1-yl acetate, (3E,5Z)-tetradeca-3,5-dienoic acid, (3E,5Z)-tetradeca-3,5-dien-1-yl acetate, (8E,10Z)-tetradeca-8,10-dienal, (8E,10Z)-tetradeca-8,10-dien-1-yl acetate, (9E,11Z)-tetradeca-9,11-dien-1-yl acetate, (6E,8Z)-pentadeca-6,8-dienal, (8E,10Z)-pentadeca-8,10-dien-1-ol, (8E,10Z)-pentadeca-8,10-dien-1-yl acetate, (9E,11Z)-pentadeca-9,11-dienal, (10E,12Z)-hexadeca-10,12-dien-1-ol, (10E,12Z)-hexadeca-10,12-dienal, (10E,12Z)-hexadeca-10,12-dien-1-yl acetate, (11E,13Z)-hexadeca-11,13-dien-1-ol, (11E,13Z)-hexadeca-11,13-dienal, (11E,13Z)-hexadeca-11,13-dien-1-yl acetate, (9E,11Z)-hexadeca-9,11-dienal, and (9E,11Z)-hexadeca-9,11-dien-1-yl acetate.
14. The method of claim 1 , wherein the conjugated diene is (7E,9Z)-dodeca-7,9-dien-1-yl acetate.
15. The method of claim 1 , wherein the metathesis product according to Formula III formed during step (ii) has a molar ratio of E olefin to Z olefin greater than 20:1.
16. The method of claim 1 , wherein the conjugated diene according to Formula I formed during step (iii) has a molar ratio of Z olefin to E olefin greater than 8:1.
17. The method of claim 1 , wherein:
the olefin according to Formula Vis oct-7-en-1-yl acetate,
the metathesis product according to Formula III is E-9-oxonon-7-en-1-yl acetate,
the phosphonium ylide according to Formula II is triphenyl(propylidene)-25-phosphane, and
the conjugated diene is E,Z-dodeca-7,9-dien-1-yl acetate.
18. The method of claim 17 , wherein the metathesis catalyst is 1,3-bis(2,4,6-trimethylphenyl)-2-imidazolidinylidene]dichloro(3-phenyl-1H-inden-1-ylidene)(triphenylphosphine)ruthenium (II):
19. The method of claim 1 , wherein the phenylphosphine ligand is a triphenylphosphine.