Studies on the Preparation of Protomycinolide IV: Enantioselective Synthesis of the C3–C9 Segment

The C3–C9 segment, (−)-16, of the polyene macrolide antibiotic protomycinolide IV (1a) was prepared in optically pure form from commercially available methyl (S)-2-methyl-3-hydroxypropionate in 12 steps giving 17% yield

Reactivity of (1-methoxycarbonylpentadienyl)iron(1+) cations with hydride, methyl, and nitrogen nucleophiles

The reaction of tricarbonyl and (dicarbonyl)triphenylphosphine (1-methoxycarbonyl-pentadientyl)iron(1+) cations 7 and 8 with methyl lithium, NaBH3CN, or potassium phthalimide affords (pentenediyl)iron complexes 9a-c and 11a-b, while reaction with dimethylcuprate, gave (E,Z-diene)iron complexes 10 and 12. Oxidatively induced-reductive elimination of 9a-c gave vinylcyclopropanecarboxylates 17a-c. The optically active vinylcyclopropane (+)-17a, prepared from (1S)-7, undergoes olefin cross-metathesis with excess (+)-18 to yield (+)-19, a C9C16 synthon for the antifungal agent ambruticin. Alternatively reaction of 7 with methanesulfonamide or trimethylsilylazide gave (E,E-diene)iron complexes 14d and e. Huisgen [3 + 2] cyclization of the (azidodienyl)iron complex 14e with alkynes afforded triazoles 25a-e

Recent Applications of Acyclic (Diene)iron Complexes and (Dienyl)iron Cations in Organic Synthesis

Complexation of (tricarbonyl)iron to an acyclic diene serves to protect the ligand against oxidation, reduction, and cycloaddition reactions, whereas the steric bulk of this adjunct serves to direct the approaches of reagents to unsaturated groups attached to the diene onto the face opposite to iron. Furthermore, the Fe(CO)3 moiety can serve to stabilize carbocation centers adjacent to the diene (i.e. pentadienyl-iron cations). Recent applications of these reactivities to the synthesis of polyene-, cyclopropane-, cycloheptadiene-, and cyclohexenone-containing natural products or analogues are presented

Studies Directed Towards the Synthesis of Protomycinaolide IV

Tricarbonyl(diene )iron complexes have been known for over 65 years but have only recently received attention concerning their use in organic synthesis. Several research groups have further shown that acyclic butadiene-iron complexes can be used in asymmetric organic syntheses as well. Furthermore, transition metal dienone complexes are beginning to receive more attention in regards to their use in organic synthesis. However, there appears to be a lack of information on the use of enolates derived from tricarbonyl- (dienone)iron complexes. Therefore, formation of a stabilized tricarbonyl(dienone)iron enolate complex and whether such a species will react with various electrophiles in a stereospecific manner needs to be addressed

Alkylation of Tricarbonyl(diene)iron Complexes: Model Studies for the Preparation of Protomycinolide IV

The alkylation of (4,6-heptadien-3-one)- and (methyl 3,5-hexadienoate)Fe(CO)3 (1 and 2) were examined (0–42% de and 69–92% de respectively). Optically active (methyl 3,5-hexadienoate)Fe(CO)3 (−)-2 was prepared by resolution of the corresponding carboxylic acid complex with α-methylbenzylamine. The alkylation of (4,6-heptadien-3-one)-Fe(CO)3 (1, 0–42% de) and (methyl 3,5-hexadienoate)Fe(CO)3 (2, 70–92% de) were examined