Wolff rearrangement photochemical

Several ring contraction routes to /3-lactams have been developed. One of the most important is the photochemical Wolff rearrangement of 3-diazopyrrolidine-2,4-diones (178), which provides a general route to 3-carboxyazetidin-2-ones (179). Lack of stereoselectivity is a problem, but facile epimerization is possible because of the electron withdrawing 3-substituent (78T1731). 

Photochemical Wolff rearrangement of 2-diazo-3-ketones, though not widely used as a source of A-norsteroids, is discussed in section V in connection with the mechanism of the important photochemical synthesis of D-norsteroids. Photochemical rearrangement of epoxy ketones is a source of A-nosteroids these rearrangements are discussed in chapter 13. Other photochemical routes to A-norsteroids are known." " ... 

The intermediacy of a ketocarbene species 4 is generally accepted for the thermal or photochemical Wolff rearrangement oxirenes 8 that are in equilibrium with ketocarbenes, have been identified as intermediates ... 

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, ... 

Zeller, K.-P. Blocher, A. Haiss, P. Oxirene participation in the Photochemical Wolff Rearrangement Mlnl-Revlewx in Organic Chemistry 2004,1, 291-308. (Review). 

The photochemical Wolff rearrangement represents a generally useful ring contraction technique. 

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

Danheiser et al. developed a new aromatic annotation methodology for the total s)mthesis of hyellazole (245) by irradiation of the heteroaryl a-diazo ketone 675 in the presence of 1-methoxypropyne (590). This reaction proceeds via the photochemical Wolff rearrangement of the heteroaryl a-diazo ketone 675 to generate a vinylketene, followed by a cascade of three pericyclic reactions. 

The Dauben-Walker approach has yielded the smallest and most strained fenestrane known to date Following the intramolecular Wadsworth-Enunons cyclization of 443 which also epimerizes the butenyl sidechain to the more stable exo configuration, intramolecular photocycloaddition was smoothly accomplished to provide 444. Wolff-ELishner reduction of this ketone afforded the Cj-symmetric hydrocarbon 445. Application of the photochemical Wolff rearrangement to a-diazo ketone 446 p,ve 447. 

A large number of diazetidinones have been synthesized by an intramolecular cyclization of haloacetylhydrazones with suitable bases (Scheme 4). A photochemical Wolff rearrangement of... 

To synthesize the very strained tricyclic system of 4 (Fig. 3.12), a photochemical Wolff rearrangement was chosen when MM predicted that the skeleton of 4 should be about 109 kJ mol-1 less stable than that of the available 5. Photolysis of the diazoketone 6 gave a high-energy carbene which lay above the carbon skeleton of... 

An hDA reaction of the thermally generated (trialkylsilyl)vinylketene 888 with diethyl ketomalonate furnishes the 5,6-dihydropyran-2-one 889 in excellent yield. Protodesilylation of the cycloadduct 889 is achieved in quantitative yield upon its exposure to methanesulfonic acid (Scheme 244). A photochemical Wolff rearrangement of the silyl diazo compound 890 can also be used to generate an intermediate diene for reaction with diethyl ketomalonate to afford the 5,6-dihydropyran-2-ones 891 (Equation 358) <19990L641>. 

The antiaromatic oxirenes 11 are extremely elusive but their potential involvement in photochemical Wolff rearrangements by equilibration with the -oxocarbenes 12 has generated both theoretical and experimental interest and the subject has been reviewed <2004MR0291>. Experimental evidence for participation of oxirenes <2004MR0291> is supported by DFT calculations that suggest that oxirene corresponds to an energy minimum <2003JMT(629)263, CHEC-III(1.03.7)215>. 

A large number of diazetidinones 15 have been synthesized by an intramolecular cyclization of haloacetylhydrazones 14 with suitable bases (Scheme 11) . A photochemical Wolff rearrangement of 4-diazo-pyrazolidine-3,5-diones 16 in the presence of some nucleophiles (H20 or alcohols) leads to diazetidinones 17 in moderate yields (Scheme 12) <1987J(P1)899>. 

The stereoselective total synthesis of tt)-campherenone was accomplished by T. Uyehara and co-workers based on a photochemical Wolff rearrangement. The bicyclic ketone was treated with 2,4,6-triisopropylbenzenesulfonyl azide (trisyl azide) under homogeneous basic conditions and the a-diazo ketone was obtained in excellent yield. The photochemical rearrangement of the diazo ketone was conducted in a THF-water mixture using a high-pressure 100 W mercury lamp. The ring-contracted acid was isolated as a 4 1 mixture of endo and exo products. 

The photochemical Wolff rearrangement of 1,3-bis(diazo)-2,3-dihydroinden-2-one is suppressed in the presence of various trapping reagents for example, cyclopropanation of benzene yields the stable norcaradienes 25 and 26. ... 

Tomioka, H., Okuno, H., Izawa, Y., Mechanism of the Photochemical Wolff Rearrangement The Role of Conformation in the Photolysis of a Diazo Carbonyl Compounds, J. Org. Chem. 1980, 45, 5278 5283. 

The reagent is generated in situ by dehydrochlorination of ethoxyacetyl chloride with triethylamine at —78°. It appears to be fairly stable at this temperature but slowly polymerizes at room temperature. It is also formed to some extent by photochemical Wolff rearrangement of ethyl diazoacetate. 

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