Rationalisation of Patterns of Competing Reactivity by X-ray Structure Determination: Reaction of Isomeric (Benzyloxythienyl)oxazolines with a Base

Three isomeric (benzyloxythienyl)oxazolines 9, 11 and 13 have been prepared and are found, upon treatment with a strong base, to undergo either Wittig rearrangement or intramolecular attack of the benzylic anion on the oxazoline function to give products derived from cleavage of the initially formed 3-aminothienofuran products. This pattern of reactivity is directly linked to the distance between the two reactive groups as determined by X-ray diffraction, with the greatest distance in 11 leading to exclusive Wittig rearrangement, the shortest distance in 13 giving exclusively cyclisation-derived products, and the intermediate distance in 9 leading to both processes being observed. The corresponding N-butyl amides were also obtained in two cases and one of these undergoes efficient Wittig rearrangement leading to a thieno[2,3-c]pyrrolone product.

Experimental and Theoretical DFT Investigations in the [2,3]-Wittig-Type Rearrangement of Propargyl/Allyl-Oxy-Pyrazolones

Here we report the synthesis of interesting 3-alkyl-4-hydroxy-1-aryl-4-(propa-1,2-dienyl)1H-pyrazol-5(4H)-ones and 9-alkyl-7-aryl-1-oxa-7,8-diazaspiro[4.4]nona-3,8-dien-6-ones, starting from 1,2-diaza-1,3-dienes (DDs) and propargyl alcohol. The reaction proceeds through a sequence Michael-type nucleophilic attack/cyclization/[2,3]-Wittig rearrangement. In the same way, the reaction between the aforementioned DDs and allyl alcohol furnished 4-allyl-4-hydroxy-3-alkyl-1-aryl-1H-pyrazol-5(4H)-ones. A DFT study was also carried out, in order to have decisive clarifications about the mechanism.

Multigram Synthesis of Difluoromethylene Phosphonic and Phosphinic Amides and Phosphine Oxides via Formal [2,3]-Sigmatropic Allyl Phosphite – Allylphosphonate Rearrangement

We describe a method for the preparation of CF2-P(V) building blocks and monomers for biological and material chemistry applications in multigram quantities based on a formal [2,3]-sigmatropic phospha-Wittig rearrangement of readily available fluoroallyl bis(amido)phosphites, amido(aryl)phosphonites and diarylphosphinites. The proposed intramolecular phosphorylation approach complements the currently prevailing phosphoryldifluoromethylation methods by providing a straightforward access to difluoromethylene phosphonate analogues bearing dialkylamino and/or aryl substituents at the phosphoryl group. An important advantage of the developed method is that it does not rely on ozone-depleting HCF2Cl and CF2Br2 necessary for the preparation of phosphoryldifluoromethylating reagents. 2,3,3-Trifluoroallyloxy P(III) derivatives substituted with two dialkylamino and/or aryl groups underwent a facile [2,3]-phospha-Wittig rearrangement to give difluoromethylene phosphonic, phosphinic and phosphine oxides on up to a 0.15 mol (30 g) scale. The reaction was extended to P(III) derivatives of 1-substituted 2,3,3-trifluoro- and 3,3-difluoroallylic alcohols readily available from carbonyl compounds and, respectively, 1,1,1,2-tetrafluoroethane and O-protected 2,2,2-trifluoroethanols. Products derived from O-(2-tetrahydropyranyl)-2,2,2-trifluoroethanol were synthesized and deprotected in a one-pot multistep protocol to give phosphonic, phosphinic and phosphine oxide analogues of α,α-difluoro-β-ketophosphonates on a multigram scale.