Diazo ketones conversion

Aryl diazo ketone conversion into the silylated diazo ketone in a one-pot procedure using a silyl triflate and then Wolff rearrangement catalyzed by triflic acid generates the stable aryl(trialkylsilyl)ketene (Scheme 7.45). 

The third operation, involving the conversion of the diazo ketone into an acid or a simple derivative thereof, is known as the Wolif rearrangement. 

The conversion of a diazo ketone to an acid amide may be accomplished by treating a warm solution in dioxan with 10-28 per cent, aqueous ammonia solution containing a small amount of silver nitrate solution, after which the mixture is heated at 60°-70° for some time. Precautions should be taken (by use of a. safety glass shield) when heating mixtures containing ammoniacal silver nitrate. 

In order to prepare an acid, a dioxan solution of the diazo ketone is added slowly to a suspension of silver oxide in a dilute solution of sodium thiosulphate If the conversion to the acid yields unsatisfactory results, it is usually advisable to prepare the ester or amide, which are generally obtained in good jdelds hj drolysis of the derivative gives the free acid. 

Padwa has reported an approach to the ring system of the ribasine alkaloids 98 [174], using an intramolecular 1,3-dipolar cycloaddition of the a-diazo ketone 99 to produce the pentacyclic skeleton 100 (Scheme 19.17). Wood [175] used an intermolecular 1,3-dipolar cycloaddition of a carbonyl ylide for the total synthesis of ( )-epoxysorbicilli-nol 101 (Scheme 19.18). The key cycloaddition in this approach is the conversion of 102 to the natural product core 103, which sets the substitution pattern around the entire ring system in a single step. 

Conversion of Diazo Ketones to a-Halo Ketones Hydro,halo-de-diazo-bisubstitiition... 

GRUNDMANN ALDEHYDE SYNTHESIS. Transformation of an acid into an aldehyde of the same chain length by conversion of the acid chloride via the diazo ketone to the acetoxy ketone, reduction with aluminum isopropoxide and hydrolysis to the glycol, and cleavage with lead tetraacetate. 

Intramolecular cycloaddition of a diazo ketone to a cyclopropene. Rhodium) II) acetate is markedly superior to copper or copper(II) sulfate as the catalyst for cyclopropanation of l,4-diacetoxy-2-butyne with /-butyl diazoacetatc. The product (1) was converted by known steps into the diazo ketone 2. In the presence of rhodium(II) acetate, 2 undergoes intramolecular cycloaddition to the cyclopropene double bond to give the highly strained tricyclic pentanone derivative 3 in 30% yield. C oppcr catalysts are less efficient for this conversion. 

Following preliminary work,528 ( )-chelidonine (118) has been synthesized from the acid (115) (obtained from methylenedioxyhomophthalic anhydride and TV-methyldimethoxybenzalimine) by its conversion into the diazo-ketone (116), cyclization of this (using trifluoroacetic acid) to the keto-lactam (117), and reduction with lithium aluminium hydride.529,530... 

The Rh-induced conversion of co-carbonyl diazo ketones 34 generates carbonyl ylides 35, and the interception of these transient 1,3-dipolar species with dipolarophiles gives rise to [3-1-2] cycloadducts 36 (Scheme 7, upper part) (96CRV223). The carbonyl group is isoelectronic with the diazene functionality of azo compounds. This prompted the investigation of co-diazenyl a -diazo ketones under similar conditions (Scheme 7, lower part). 

Scheme 9 Rhodium(ll)-induced conversion of a-diazenyl-a -diazo ketone 42 [n = 0) into cyclic azomethine imines 44 and 45.

The efficient oxidative ring-opening of diazetidinone 40 with ferf-butyl hypochlorite forming acid chloride 41 and its conversion into a-diazenyl diazo ketone 42 upon treatment with diazomethane (Scheme 8) was anticipated to be transferable to the five-membered homologue 50. However, 5,5-dimethyl-2-phenylpyrazolidin-3-one (50) (96LA272,... 

Scheme 17 Conversion of jS-diazenyl-a -diazo ketone 58 into azomethine imines 70 and 71. Selective interception of the transient 6-ring isomer 71 with N-methyi-...

Extension of the C-tether to m = 2 can be achieved by subjecting diazo ketone 58 to the Wolff rearrangement using silver benzoate, triethyl-amine and methanol. Hydrolysis of the resulting methyl 4-methyl-4-[(E)-phenyldiazenyllpentanoate (74) (94%) yields the acid 75 (84%). Conversion of 75 into the mixed anhydride 76 followed by treatment with diazomethane gives 1 -diazo-5-methyl-5-[(E)-phenyldiazenyl]hexan-2-one (77) in low yield (19%) and methyl ester 74 (78%) (Scheme 18). 

Scheme 18 Conversion of /i-diazenyl-ot -diazo ketone 58 into y-diazenyl-ot -diazo ketone 77.

Scheme 19 Conversion of y-diazenyl-a -diazo ketone 77 into azomethine imine 78 and 79. Interception of 6-ring azomethine imine 78 with N-methylmaleimide to yield cycloadduct 80.

Cholic acid has been converted into 5/S-cholestane-3a,7a,12a,25-tetrol and the 3a,7a,12a,24,25-pentols. Extension of the side-chain involved conversion of the acid via the diazo-ketone (361) into a homocholanic ester derivative (362). Grignard reaction then gave the 25-hydroxy-cholestane (363). Dehydration followed by hydroxylation (OSO4) afforded the 24,25-diols with a little of the 25,26-diol. ... 

Photo-Wolff rearrangement in cyclic o-diazo ketones is accompanied by ring contraction. Photochemically induced conversion of the a-dlazocyclopentanone (65) into the cyclobutane... 

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