Propargyl acetates 1,2 migration

This cascade proved to be quite complex, successively involving a [3,31-sigma-tropic shift of the propargyl acetate, 1,2 migration of this acetate, and cycloisomerization (Scheme 3.47). 

Allenylboranes can be prepared by treatment of propargylic acetates with butyl-lithium and a trialkylborane [19]. The reaction proceeds by initial formation of an alkynylboronate followed by migration of an alkyl group from boron to carbon (Eq. 9.17). 

Propargylic acetates in equation (80) react differently in a process that also takes place via a 1,3-acyl migration. Thus, the reaction of such substrates gives bicyclo[3.1.0]hexenes, which can be transformed into cyclohexenones on treatment with K2CO3 in MeOH. As shown in equation (81),... 

The acyl migration of benzylic acetates was also applied for the synthesis of indenes (equation 87). Isomeric indenes were also obtained as minor products. The transformation was actually shown to proceed via allenes, which could be independently prepared by Ag(I)-catalyzed 1,3-acetate migration from the same starting materials. Propargylic sulfides and dithioacetals undergo similar transformations as propargylic carboxylates to give indene derivatives with Au(I) or Au(III) catalysts. 

The gold complex catalysed tandem l,2-/l,2-bis-acetoxy migration in 1,4-bis-propargyl acetates to form 2,3-bis-acetoxy-1,3-dienes has been reported... 

The reactions of allenyl and propargyl derivatives of boron, silicon or tin with carbonyl compounds or acetals take place with double-bond migration (Se reactions). Therefore, allenyl derivatives will lead to homopropargyl alcohols and propargyl analogs to allenyl alcohols. 

Dithiobenzoates PhCS2R (R = allyl, propargyl, or benzyl) add to dimethyl acetylenedicarboxylate to form the dithioles (288) with migration of the group R. Piperidine catalyses the addition of acetylenic ketones Ar COC=CAr to 4-methylbenzene-l,2-dithiol to give the benzodithioles (289). The reaction of the acetal BrCH2CH(OEt)2 with ethanedithiol yields a mixture of the bis(dithiolan) (291) and derivatives of dithian, which are formed, respectively, from the cations (290) and (292). ... 

Methyl-, hydroxyethyl-, hydroxypropyl-, and carboxymethyl starches, starch acetates, succinates, alkenyl succinates (Fig. 2), adipates, and phosphates, are all well-known products. Furthermore, special derivatives have also been prepared, such as vinyl-, silyl-, ° or propargyl starches, as reactive intermediates for fiirther fime-tionalization. Unusual substitution patterns can also be established by highly selective deacetylation with alkyldiamines and subsequent introduction of such functional groups as sulfates. From die analytical point of view, the most important aspects are stability under alkaline (mediylation) and acidic or Lewis-acidic (depolymerization) conditions, reactivity (such as migration, rearrangement, further substitution or addition reactions, or any intramolecular reaction), and polarity (lipophilic/hydrophilic, ionic/nonionic, acidic/basic). These properties mainly determine the analytical... 

Next, Gevorgyan et al. disclosed an alternative route to tetrasubstituted and even fused furans via a transition metal-catalyzed migratory cydoisomerization of skipped propargylic systems. Thus, syntheses of 3-acyloxyfurans 69 from alkynyl acetates 68 occurred with a formal 1,2-migration in the presence of 5 mol% of Ag-catalyst at room temperature (Scheme 8.28) [139,140[. Several other transition metals such as Cu(II),... 

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