Rearrangements and Cyclizations

One route to 0-vinyl derivatives involves LiPdCl4-calalysed exchange with vinyl acetate[l]. Rearrangement and cyclization occur concurrently to give 1-acylindoles. 

Claisen rearrangementThe allyl ether 1 when heated rearranges and cyclizes slowly and in low yield to the dihydrobenzofuran 2. However, the dianion (NaH) of 1 rearranges in refluxing DMF mainly to the isomeric dihydrobenzofuran 3, a precursor to the antibiotic ( )-atrovenetin (4). 

Phenyl- and 2-(2-thienyl)-3,3-dimethyl-3//-pyrroles (58) were obtained by the reaction of the corresponding ketoximes 56 with acetylene catalyzed by MOH (M = Na, K) in DMSO. The reaction intermediate observed is the corresponding O-vinyl oxime 57 which undergoes [3,3] sigmatropic rearrangement and cyclization to products 58 (equation 24). The yield of the products obtained strongly depends on the structure of the ketoxime . 

If the side chain contains an alkynyl moiety a similar process occurs, as seen in Equation (162). The propynylthio-pyrimidines 436 undergo thermal rearrangement and cyclization to give quite good yields of 437 <2004TL6075>. 

Anhydro-D-glucitol tetraacetate was envisaged as opening to form the intermediate 32 which, through a series of rearrangements and cyclizations, yields 1,4-anhydro-D-glucitol, 1,4-anhydro-D-man-... 

In an interesting transformation, reaction of benzoyl trimethylsilane with lithium enolates derived from various methyl ketones gives rise to 1,2-cyclopropanediols, predominantly with the cis configuration, in good yields (Scheme 77). The reaction, which proceeds through addition, Brook rearrangement and cyclization, is also successful with a,/l-unsaturated acyl silanes vide infra, Section IV.D)187. 

Some /J-heteroatom substituted a,/J-unsaturated acyl silanes react with methyl ketone enolates in a stepwise stereoselective cyclopentannelation process, formally a [3 + 2] annelation, which may proceed through aldol reaction followed by Brook rearrangement and cyclization (Scheme 111)223. 

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