The total synthesis of chlorophyll a

Electrochemical reduction of oxygen : an alternative method to prepare active CoN4 catalysts

Bacteriochlorins are attractive candidates for a wide variety of photochemical studies owing to their strong absorption in the near-infrared spectral region. The prior acid-catalysis conditions [BF(3) x O(Et)(2) in CH(3)CN at room temperature] for self-condensation of a dihydrodipyrrin-acetal (bearing a geminal dimethyl group in the pyrroline ring) typically afforded a mixture of three macrocycles: the expected 5-methoxybacteriochlorin (MeOBC-type), a 5-unsubstituted bacteriochlorin (HBC-type), and a free base B,D-tetradehydrocorrin (TDC-type). Here, a broad survey of >20 acids identified four promising acid catalysis conditions of which TMSOTf/2,6-di-tert-butylpyridine in CH(2)Cl(2) at room temperature was most attractive owing to formation of the 5-methoxybacteriochlorin as the sole macrocycle regardless of the pyrrolic substituents in the dihydrodipyrrin-acetal (electron-withdrawing, electron-donating, or no substituent). Eleven new dihydrodipyrrin-acetals were prepared following standard routes. Application of the new acid catalysis conditions has afforded diverse bacteriochlorins (e.g., bearing alkyl/ester, aryl/ester, diester, and no substituents) in a few days from commercially available starting materials. Consideration of the synthetic steps and yields for formation of the dihydrodipyrrin-acetal and bacteriochlorin underpins evaluation of synthetic plans for early installation of bacteriochlorin substituents via the dihydrodipyrrin-acetal versus late installation via derivatization of beta-bromobacteriochlorins. Treatment of the 5-methoxybacteriochlorins with NBS gave regioselective 15-bromination when no pyrrolic substituents were present or when each pyrrole contained two substituents; on the other hand, the presence of a beta-ethoxycarbonyl group caused loss of regioselectivity. The 15 new bacteriochlorins prepared herein exhibit a long-wavelength absorption band in the range 707-759 nm, providing tunable access to the near-infrared region. Taken together, this study expands the scope of available bacteriochlorins for fundamental studies and diverse applications.

Expanded scope of synthetic bacteriochlorins via improved acid catalysis conditions and diverse dihydrodipyrrin-acetals.

A series of different counterions have been incorporated into polypyrrole electrochemically. These include toluenesulphonate (TS), pyrenesulphonate (PSA), Pyrene-1,3,6,8-tetrasulphonate (PTSA), dodecylbenzenesulphonate (DBS), 1,2-bis (decyloxycarbonyl)ethane-1-sulphonate (DOCES), octachloro-dirhenate (Re2Cl8) and tetraphenylborate (TPB). Electrochemical redox behaviour of the pyrrole monomer and the polypyrrole incorporating these different anions was investigated and is discussed. From scanning electron microscopy (SEM), it is shown that the different counterions incorporated strongly affect the morphology of the polymer films, they vary from fully dense to open structures. Chemical and physical characterization of the materials is presented and suggests that the sizes of the different counterions incorporated also influence the polymer chain structures, packings and their thermal stabilities. The pyrrole to counterion stoichiometries are very different, ranging from 1 to 13. In most cases, the redox potential of the polymer can be related to the size of the counterion but the electrical conductivity, which ranges from 2×10−3 to 50 Scm−1, is not simply related to the counterion but is dependent on both chain structure and bulk morphology.

The influence of unusual counterions on the electrochemistry and physical properties of polypyrrole

TosMIC is the acronym for 4-tolylsulfonylmethyl isocyanide or tosylmethyl isocyanide. It is the best-known member of a series of about 25 sulfonyl-substituted methyl isocyanides RSO2CH2NC collected in Chart 1 (p. 426). TosMIC is a multipurpose synthetic reagent. It is by far the most versatile synthon derived from methyl isocyanide. This chapter provides a complete account of the synthetic uses of TosMIC based on a literature search closed in January 1996, and supplemented with further data available to the authors. Also included are applications of some of the more important TosMIC homologs (TosCHRNC).



TosMIC is the only commercially available sulfonylmethyl isocyanide. It is a stable, colorless, practically odorless solid, which can be stored at room temperature without decomposition.



Four brief review papers on the chemistry of TosMIC have appeared, in 1980, 1987, 1993, and 1995. Several reviews on the chemistry of isocyanides in general are available.



An effort has been made to make this chapter as complete as possible, in coverage both by tables and by references, with respect to the immediate objective: a survey of the “Synthetic Uses of TosMIC.” Emphasis is on the primary products derived from reactions of TosMIC and related isocyanides, with limited reference to the further utilization of these products. Thus, the next section gives a complete account of reductive cyanation, the conversion of aldehydes or ketones into cyanides with the use of TosMIC, but for obvious reasons synthetic applications of the product cyanides are not treated in this chapter. One of the subsequent sections describes the application of TosMIC to the synthesis of pyrroles, including 2,3-divinylpyrroles, which are important precursors in a new synthesis of indoles. This latter transformation, made possible by the easy availability of the precursors through TosMIC chemistry, is afforded brief coverage.



As a rule, reference to preliminary papers has been omitted when the same information is available from the corresponding full papers. The patent literature is covered highly selectively and is cited only when providing new and relevant information. Negative results of reactions are reported in the text or tables only when at least some relevant information is available with respect to the conditions of such unsuccessful attempts.


Keywords:

tosylmethyl isocyanide;
4-tosylsulfonylmethyl isocyanide;
sulfonyl;
methyl isocyanide;
isocyanide;
synthetic application;
synthetic utility

E. Legoff

Papers

Synthesis and michael reaction of 3,4‐dimethylpyrrole