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Halolactonization 8-lactone synthesis

As mentioned earlier in the discussion of cyclizations leading to (3-lactones, the (3-lactones formed from halolactonization of 1,4-dihydrobenzoic acids readily rearrange to produce bridged ring y-lac-tones.19 In some cases, the substitution pattern favors formation of the y-lactone even under conditions of kinetic control (equation 23).20 Synthesis of a variety of y-lactones by iodolactonization of dihydroben-zoic acid derivatives has been reported recently by Hart (equation 24).91 Attempted iodolactonization of the acid in the case where R = H resulted primarily in an oxidative decarboxylation however, iodolactonization was effected using the amide derivative. [Pg.374]

Halolactonizations have been used extensively for achieving high degrees of functionalization in a regio- and stereo-controlled manner. The conversion of (284) into (285 equation 101) is a key step in Corey s prostaglandin synthesis to prepare the central intermediate (286). For p,7-unsaturated acids like (287) the P-lactone (288) is formed under kinetic control, which then equilibrates to the 7-lactone isomer (2 9 equation 102). ... [Pg.361]

Lactones, cyclic esters such as compound A, are prepared by halolactonization, an addition reaction to an aikene. For example, iodolactonization of B forms lactone C, a key Intermediate In the synthesis of prostaglandin PGp2a (Section 4.15). Draw a stepwise mechanism for this addition reaction. [Pg.398]

Figure 11.21 shows the use of halolactonization in the total synthesis of the antibiotic erythronolide B. In this case, only the formation of the six-ring lactone is possible—if the carboxylate attacked the other end of the bromonium ion, an unfavorable seven-membered ring would have been generated. Notice that for both the key reactions, the bromine and the oxygen of the lactone are on opposite sides of the original double bond. [Pg.434]


See other pages where Halolactonization 8-lactone synthesis is mentioned: [Pg.171]    [Pg.16]    [Pg.213]    [Pg.122]    [Pg.529]    [Pg.124]   
See also in sourсe #XX -- [ Pg.6 , Pg.366 ]

See also in sourсe #XX -- [ Pg.366 ]

See also in sourсe #XX -- [ Pg.6 , Pg.366 ]

See also in sourсe #XX -- [ Pg.366 ]




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