Cyclization reactions Wolff rearrangement

A similar synthesis of mechanistic interest rather than preparative value involves the thermal reaction of dimethyl 2,5-bisdiazo-3,4-diketoadipate (89, Scheme 23) with benzofuran (91)." The presumed intermediate is the pyrone cation 90 produced from the adipate 89 by the Wolff rearrangement, cyclization, and loss of nitrogen. Electrophilic substitution then affords the benzofuran 92, which can be isolated. Ring opening and cyclization of the resultant ketene 93 then affords the dibenzofuran 94 in poor (0.4%) yield. 

A tandem Wolff rearrangement reaction followed by cyclization leads to the formation of thieno[3,2-f]pyrans in moderate yields as shown in Scheme 26 <1998T6457>. A key step of the reaction involves thermolysis of diazoketophosphonate 97. 

Using Ph3P to induce Staudinger reaction of a-azidocinnamic esters as well as Wolff rearrangement of a-diazo ketones, two types of mutually reactive molecules are formed. The natural course for aza-Wittig reaction is pursued to produce cyclization-prone ketene imines. ... 

An alternative synthetic approach to obtain cyclic enaminones from bromodiazoacetone 291, primary amines, and alkynes is based on a sequential aza-Michael addition/Wolff rearrangement, and nucleophihc ketene cyclization which was performed in a one pot fashion has been reported (Scheme 93) (20110L2147). Using this protocol, a collection ofenaminone reaction products 292—297 was obtained in satisfactory yields (Scheme 93). 

The 5-7V-tosylamino substituted a-diazo-P-keto carbonyl compounds 101 were obtained from the reaction between diazo ketone 100 and the tosylimine 99 in the presence of TiCU in dichloromethane. The diazo ketone 101 underwent Wolff rearrangement in benzene upon irradiation with a high-pressure Hg lamp to afford 102, which subsequently cyclized to give the expected y-lactam derivatives. ... 

The first total synthesis of the antibiotic acanthodoral (1) 118 has been achieved from 3-methyl-2-cyclohexen-l-one in 19 steps in 2.1% overall yield. This synthesis involves the use of a Pd-ene reaction in the presence of CO to form the endocyclic alkene 116, a nonreductive acyl radical cyclization and ring contraction by the Wolff rearrangement of ll ." ... 

Finally, not all applications of Cul involve organocuprates or related reagents. For example, Corey used Cul to catalyze intramolecular diazoalkene cyclization reactions, and Yates used Cul to catalyze the Wolff rearrangement of diazo ketones. Flouse recommended CuL(SBu2)2 for the intermolecular cyclo-propanation of alkenes with a-diazo ketones. The intermediates are undoubtedly organocopper species of some kind, perhaps Cu-carbene complexes however, it should be noted that Cu and Cu are more commonly used as catalysts in conjunction with diazo compounds. ... 

In the initial applications of Diels-Alder chemistry to yohimbine alkaloid synthesis, the Kametani (24-27) and Takano (28) groups have both examined reactions between furan derivatives and maleic anhydride. In the initial investigations of Kametani and his coworkers (24) (Scheme 3.10), the Diels-Alder adduct (57) of furan and maleic anhydride underwent bromolactonization to give the tricyclic carboxylic acid 58 (94). This compound has four [C(15), C(16), C(17), and C(18)] of the five contiguous stereocenters of the reserpine E-ring in place. Acid 58 was converted to diazoketone 59 which underwent Wolff rearrangement followed by tryptamine trapping to afford amide 60. Bischler-Napieralski cyclization of this substance afforded the tetracyclic... 

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