Stevens rearrangement Subject

Recently, Padwa s group has encountered an interesting Stevens rearrangement sequence which occurred when a-diazo ketoamide 142 was subjected to Rh(II)-catalyzed conditions.66 In the presence of DMAD, the expected product 146 derived from the trapping of dipole 145 was isolated (57%) together with the unexpected lactam 144 (23%). In the absence of DMAD, lactam 144 was the only product obtained in 62% yield. The formation of 144 was attributed to the initial generation of ammonium ylide 143 followed by a [l,2]-benzyl shift. 

An alternative to SO2 expulsion is via the intermediate tetrathiacyclophane, generated by oxidative cyclization of a tetrathiol, which upon desulfurization afforded the dithiacyclophane <01JA4704>. Subsequent methylation with (MeO)2CHBF4, followed by the Stevens rearrangement gave the ring-contracted, Ws-thiomethyl ether that was S-methylated and subjected to a Hofmann elimination affording 3, which is in a 1 20 equilibrium with 4. 

The reaction of 5-acetoxy-5,6,7,8-tetrahydroisoquinoline 109 with Mel followed by reduction afforded the octahydroisoquinoline 110, which upon treatment with ethyl chloroformate followed by hydrolysis gave 111. The condensation of 111 with 2-bromoisovanillin afforded 112, which was reduced to give the benzyl alcohol intermediate 113. Heck reaction of 113 led to the formation of 0-ring affording 115. The yield of the above intramolecular cyclization was increased significantly via prior protection of the alcohol in 113 as silyl ether 114. Conversion of 115 to benzyl chloride 116 was achieved via the treatment with NCS and triphenylphosphine. Further, Heck reaction of 116 afforded the tertiary amine 117 via an intramolecular A -benzylation. The amine 117 was converted into the corresponding iV-methylammonium iodide 118, which was then subjected to Stevens rearrangement with PhLi to afford ( )-desoxycodeine 119 in 83 % yield. ... 

A syn displacement of the bromine by benzylamine in the presence of triethylamine led, by a Sn2 reaction, to the a and p amino compounds which were separated into 326 (18%) and 327 (81%) respectively. The dichloroacetamide 328 derived from the latter, when subjected to the action of tri-n-butyltinhydride (2eq) and 2,2 -azobisisobutyronitrile underwent a 5-ero ring closure to furnish via the radical 329, the hydrooxindole 330 (51%) and significant amount of the rearrangement product 331 (30%). The latter is believed to be formed by fragmentation of the cyclohexadienyl radical 332 generated from the cyclohexyl radical 329. On diborane reduction, 330 provided the cis hydroindole 333, which on 0,N-debenzylation afforded ( )-c -fused bicyclic aminoalcohol 334, a compound that had been previously cyclised with formaldehyde to ( )-elwesine (320) by Stevens et al [85]. 

Other reactions that are very likely subject to the persistent radical effect are molecular rearrangements such as the Meisenheimer, amineimide, Wit-tig, Stevens, and sulfenate rearrangements of Scheme 20, for which evidence for radical intermediates has been accumulated.77... 

From Diazo-compounds. The Wolff rearrangement of a-diazo-ketones has been reviewed and a discussion of the Bamford-Stevens reaction and its associated mechanisms has appeared. The details of a cryochemical synthesis of cyclo-propanone from keten and diazomethane have been described, as have syntheses of cyclopropanone and cyclopropanone acetal. The photolysis of 1-diazobutane, resulting in methylcyclopropane, has been subjected to physico-chemical study. 

---