Metal-encapsulated porphyrazines: synthesis, x-ray crystal structure and spectroscopy of a tetratin-star-nickel(porphyrazine)S8 complex

Abstract

Optimization of the Julia-Lythgoe procedure7 used to couple the two fragments 5 and 8 required extensive experimentation (Scheme 11). Phenyllithium was found to be the base of choice for deprotonation of 5 selectively at C( 17). The use of weaker bases, e.g., LDA and Et2NLi, and stronger bases, e.g., tert-and n-butyllithium, resulted in insufficient deprotonation and concomitant formation of arylic anions,* respectively. The presence of Na2HP04 in the reductive elimination (the second reaction of step a) served to retain the C(7) acetate in product 119 After selective acetylation at C(20), affording triol 13 (step b), and conversion of this bis allylic alcohol to the corresponding bis ester (14) (step c), the remaining C(3) hydroxyl group was oxidized and the product aldehyde was treated with chiral enolate reagent 7 (step d, reaction ii) to provide as the major product the 3-hydroxy (instead of MOM-protected 3-hydroxy) seco-acid thiol ester 15. The two reactants, the aldehyde derived from 14 and enolate 7, constitute a mismatched pair,5 and in this context, the stereoselectivity of 3:l observed in this aldol reaction should be appreciated.Macrolactonization and Functional Group Manipulation. Thiol ester 15 was sensitive toward acid, but selective removal of its acetonide was achieved with the retention of the methyl acetal functionalities to provide 16 as one diastereomer. This compound was the seco-acid derivative originally designed for macrolactonization at the risk that there are three sites [the C(3), C(25), and C( 26) hydroxyl groups] available for lactonization. Since all attempts at the direct lactonization of 16 with a thiophilic metal cationlo failed, 16 was converted to carboxylic acid 17 with temporary protection of the three hydroxyl groups." It was only after numerous experiments that 17 was macrolactonized in a yield of 51% with a combination of DCC (10 equiv), pyridine (100 equiv), and PPTS (IO equiv).I2*I3 Spectral inspection of the product 18 indicated that the lactonization site was indeed C(25)14 and that the C(9) methyl acetal and C(7) acetate were hydrolyzed under the reaction conditions. After macrolactonization there still remained a problem: the C( 19) methoxy group15 resisted acid hydrolysis probably because of the presence of the electronwithdrawing C(20) acetate group in addition to the excessive steric congestion around the C(19) center. Surprisingly, removal of the acetate followed by acidification solved the problem to give 19.16The triacetate 20 derived from 19 was found to be identical with the acetate of Il7 isolated from the natural source to establish the correctness of the stereostructures assigned to all the synthetic intermediates. Selective dation of the C(26) hydroxyl group of 19 followed by acetylation and desilation completed the synthesis of 1 and confirmed as identical the two samples of synthetic and natural origin.'*J9 (7) Julia, M. Pure Appl. Chem. 1985, 57, 763. (8) Gais, H.-J.; Ball, W. A.; Bund, J. Tetrahedron Letr. 1988, 29, 781. (9) For instance, see: Grcck, C...

Comparative study of metal‐porphyrins, ‐porphyrazines, and ‐phthalocyanines

“…For these reasons, there have been numerous experimental studies of MPs and MPc's, whereas metal porphyrazines (MPz's) have received much less attention since their early synthesis,14 probably due to the lack of an efficient synthetic method for making soluble derivatives 15. In recent years, however, some interesting discoveries involving Pz's have been made,15–18 which augur a bright future for their applications.…”

Synthesis and photophysical properties of a series of octaphenyl-porphyrazine–magnesium

“…In these years, many new porphyrazines with novel electronic and magnetic properties came to sight [1][2][3][4]. But studies of the photophysical and photosensitizing properties of porphyrazines are relatively recent [5].…”

Preparation and Electrochemical Properties of 1,4,8,11,15,18,22,25‐Octalkylphthalocyanines Containing Four Trithiole Rings

“…[21] In contrast, peripheral modification of phthalocyanines through the S-C bond cleavage of thioethers is rare. [15] Deprotection and subsequent functionalization of 4b, 4c, and 4b-Ni was thus tried.…”