FORMATION AND PHOTOCHEMICAL WOLFF REARRANGEMENT

FORMATION AND PHOTOCHEMICAL WOLFF REARRANGEMENT OF CYCLIC a-DIAZO KETONES D-NORANDROST-5-EN-3 -0L-16-CARB0XYLIC ACIDS, 52, 53 FORMIC ACID, AZIDO—, tert-BUTYL ESTER, 50, 9 Formylation, with acetic formic anhydride, 50, 2 p-FORMYLBENZENESULFONAMIDE, ... 

FORMATION AND PHOTOCHEMICAL WOLFF REARRANGEMENT OF CYCLIC a-DIAZO KETONES D-NORANDROST-5-EN-3P-OL-16-CARBOXYLIC ACIDS... 

A method for the synthesis of highly substituted aromatic and heteroaromatic hydroxy compounds is the photochemical Wolff rearrangement of an unsaturated a-diazo ketone in the presence of an alkyne. The product, an alkenylcyclobutenone, undergoes ringopening and recyclization to a phenol (equation 60). Three examples of the reaction are the formation of the naphthols 587 and 588 and that of the hydroxybenzofuran 589. Complexes 590 (R = alkyl or aryl r-alkyl or Me3Si), produced from THF, alkynes and... 

Photochemical Wolff rearrangement of 6-diazo-cyclohexadienones 47, 49, 51 and 53 led to the formation of 2,3-benzopentaftilvenone 48, pentafulvenone 50, dibenzopentafulvenone 52 and 2,4-di-ter/-butylpenta-fulvenone 54 respectively. ... 

The key step of the Amdt-Eistert Homologation is the Wolff-Rearrangement of the diazoketones to ketenes, which can be accomplished thermally (over the range between r.t. and 750°C, photochemically or by silver(I) catalysis. The reaction is conducted in the presence of nucleophiles such as water (to yield carboxylic acids), alcohols (to give alcohols) or amines (to give amides), to capture the ketene intermediate and avoid the competing formation of diketenes. 

Grellmann, K.-H., Kiihnle, W., Weller, H., and Wolff, T. (1981) Photochemical formation of dihydrocarbazoles from diphenylamines and their thermal rearrangement and disproportionation reactions. Journal of the American Chemical Society, 103, 6889-6893. 

Fig. 11.24. Mechanisms of the photochemically initiated and Ag(I)-catalyzed Wolff rearrangements with formation of the ketocarbene E and/or the ketocarbenoid F by dediazotation of the diazoketene D in the presence of catalytic amounts ofAg(I). E and F are converted into G via a [1 2]-shift of the alkyl group R1. N2 and an excited carbene C are formed in the photochemically initiated reaction. The excited carbene usually relaxes to the normal ketocarbene E, and this carbene E continues to react to give G. The ketocarbene C may on occasion isomerize to B via an oxacyclopropene A. The [l,2-]-shift of B also leads to the ketene G.

Nitrogen extrusion from a-diazoketone and the 1,2-shift can occur either in a concerted manner or stepwise via a carbene intermediate known as the Wolff rearrangement (Scheme 2.58). a-Diazoketones undergo the Wolff rearrangement thermally in the range between room temperature and 750°C in gas-phase pyrolysis. Due to the formation of side products at elevated temperatures, the photochemical or silver-metal-catalyzed variants are often preferred that occur at lower reaction temperature. 

Novolak diazonaphthoquinone positive-tone resists, the most important imaging system of semiconductor production today1510,1511 is an archetypal example of the industrial applications of photochemistry. Novolak is a phenol formaldehyde polymer (Bakelite) that dissolves in aqueous hydroxide, but the addition of a small amount of the diazonaphthoquinone 585 dramatically decreases the solubility. When irradiated, 585 undergoes the photo-Wolff rearrangement (see also Scheme 6.171), leading to ring contraction and subsequently to carboxylic acid formation (Scheme 6.284). Such a photochemically altered site is readily soluble and can be removed with a basic developer solution. 

Recently, other photochemical and thermal retro-Wolff rearrangements have been examined by several researchers.52 55 Under flash vacuum and pulsed pyrolysis conditions, Wentrup and co-workers observed the formation of (cyanovinyl)ketenes from aza fulvenones. Additionally, Moore and co-workers have done extensive work on the gas-phase photochemistry and molecular dynamics on the C2H2O surface using state-resolved spectroscopic methods. 

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