Rearrangements Chapman

SCHEME 9.1 Synthesis of N-protected glycosylamines employing the Chapman rearrangement. 

One of the new rearrangement reactions is a dyotropic rearrangement [6,7], It is an uncatalyzed process in which two o-bonds simultaneously migrate intramolecularly. This rearrangement is further classified as type 1 and type 2. Type 1 consists of reactions in which the two o-bonds interchange positions (e.g., rearrangement of nitrile oxide into isocyanate). In contrast, in type 2, the two o-bonds do not interchange positions. 

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The use of cycloadditions for synthesizing medium-sized ring lactams is more or less restricted to the generation of seven-membered rings. The simplest method to generate azepinones seems to be the [6-1-1] reaction of a 1,6-dicar-boxylic acid chloride 148/152 and a phosphinimine 149, the in situ formed chloro enamine 150 underwent a Chapman rearrangement to give a cyclic imide 151/153 (Scheme 28)] [36]. 

The reactions of vinyl ethers with sulfonyl azides have been described by several authors.260-273-275 From dihydropyran the arylsulfonimines of 5-valerolactone (87) are obtained. These compounds rearrange at ca. 180° into N-arylsulfonyl-2-piperidones (88) (Chapman rearrangement).276... 

The carbonyl compound (161), obtained by hydrolysis of 3-benzoyl-2(3//)-benzofuranone (160),407 gives the benzofuran derivative (150) (R1 = H, R3 = COOH, Ar = Ph). The same occurs with the product of the abnormal Chapman rearrangement 395 of iV-phenylbenzimino o-(carbomethoxymethyl) phenylether. 

With excess HFA a dioxolaneimine 99a is formed from a typical isonitrile reaction mentioned in previous sections. Acidification yields the unsubstituted five-membered ring 99, which is the parent compound of alkylated dioxolanes 99b-e available from isonitriles (R = Me, Et, t-Bu, c-CgHu) 111, 188). Whether the imine structure 99 or the ketone structure 101 has to be assigned to the hydrolysis product is not known. The Chapman rearrangement has been proved in the following system [Eq. (86)] 190). Treatment of 98 with strong bases like l,8-diazabicyclo[5.4.0]undec-7-ene (DBU) yields a spirocyclic compound 100 with elimination of HCN the structure of 100 has been derived by spectroscopic methods 193). The reaction of 98 with HFA X HjO (91) in sulfuric acid produces a l,3-dioxolan-(4)one 112). 

Mercaptodicyanamides react with two molecules of HFA to form six-membered heterocycles 104b-d. Derivative d, a recrystallizable solid, has been isolated. Pyrolysis yields triazinones I05b-d via Chapman rearrangement with evolution of HFA. The unsubstituted six-membered ring 105a is... 

At higher temperatures (from —10 to +10 °C) the transmetallation products 145 undergo a gradual conversion to the O-aUcylation products 146 by chlorine migration from carbon to germanium. Further increase in temperature (up to 60 °C) results in isomerization to the A-alkylation products 142-144. The latter reaction is similar to Chapman rearrangement, although it occurs under remarkably mild conditions. The half-lives for conversion of imidates 146 (R, R = (CH2)n, n = 4, 5) are 13 and 25 min, respectively... 

CHAN Reduction of acetylenes 60 CHAPMAN Rearrangement 61 Chen 390... 

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