First Examples of Spirooxaphosphirane Complexes

Abstract

b S Supporting Information S piroalkanes such as spiropentanes (I) have been intensively studied by experimentalists as well as theoreticians. 1 Although spiroheterocycles are present in a large number of natural products 2 and show physical properties of particular interest, 3 the area of phosphorus-containing spiroheterocycles is deeply underdeveloped and, moreover, the research has been focused on phosphorusÀcarbon ring systems 4 such as the phospha-spiropentanes IIÀIV (Scheme 1). Whereas most derivatives of II 5,6 and III 7 were bound to a transition-metal center, 8 the only known derivative of IV 9 (all tert-butyl substituted) was obtained nonligated. To the best of our knowledge, nothing is known about spiroheterocycles that have another heteratom (as in V) and, therefore, the question of the effect of a (very) polar ring bond on structure and reactivity has not been addressed before.Theoretical investigations on monocyclic oxaphosphirane derivatives revealed a considerable ring strain of 23.2 kcal/mol for the parent system (RI-CCSD(T)/TZVPP), while for trimethyloxaphosphirane pentacarbonylchromium(0) a slightly smaller mean value of 22.0 kcal/mol was obtained (RI-SCS-MP2/ TZVPP); 10 this transition-metal effect was not studied further. Recent experimental studies on acid-induced ring opening 11 of monocyclic oxaphosphirane complexes have demonstrated that they have become valuable new building blocks which deserve further study. On the basis of the convenient methodology for oxaphosphirane complexes that was developed recently, 12 we felt attracted by the idea to establish a method that enables access to spiroheterocycles of type V as new ligand systems, which have various ring sizes and various heteroatoms E.Here, we report the facile synthesis of the first spirooxaphosphirane complexes (E = O) using the Li/Cl phosphinidenoid complex route and cyclic ketones. Furthermore, a first attempt to access a phospha-spiropentene complex derivative using this particular route is described. ' RESULTS AND DISCUSSIONChlorine/lithium exchange in complex 1, 13 using tert-butyllithium in the presence of 12-crown-4 at low temperature, led to the transient Li/Cl phosphinidenoid complex 2, 12a which was reacted in situ with cyclohexanone, cyclopentanone, and cyclobutanone, thus yielding the spirooxaphosphirane complexes 3a,bÀ5a,b (Scheme 2).In all reactions the two isomers a and b were formed (3a,b, 23:77; 4a,b, 55:45; 5a,b, 69:31; determined via integration of the 31 P{ 1 H} NMR spectra); only in the case of complexes 3a,b was the major isomer the b isomer, while in all other cases (4a,b and 5a,b) was the minor isomer. Column chromatography yielded only isomer 3b in pure form (see below), while the other complexes could not be separated and thus were purified and characterized as mixtures. Despite this, the structures of complexes 4a and 5a were unambiguously confirmed by single-crystal X-ray analysis; for selected data see Figures 1 and 2. Scheme 1. Spiropentane (I), Phospha-Spiropentane Derivatives IIÀIV, and Phospha-S...

The 3‐Acetyloxaphosphirane/1,3,2‐Dioxaphosphol‐4‐ene Rearrangement

“…Reaction of Li/Cl phosphinidenoid 2 and diketones 3a/ 3b. resonances to P-C exo atropisomers of 4b/4bЈ owing to the orientation [15] of the CH(SiMe 3 ) 2 group relative to the W(CO) 5 group, which can be s-cis or s-trans (H-C-P-W dihedral angle). As expected for the symmetrical 1,3,2-dioxaphosphol-4-ene ring structure in 5a, only one carbon resonance was found for the ring-bound methyl groups (δ =11.0 ppm, 3 J P,C = 5.9 Hz) and the C-4/C-5 ring atoms (δ =132.2 ppm, 2 J P,C = 4.…”

Reaction of Li/Cl phosphinidenoid complexes with a phosphite substituted ketone: access to complexes with a novel mixed-valence polycyclic P,C-ligand system

“…Li/Cl phosphinidenoid complexes 2a 7a and 2b 7c were formed via chlorine/lithium exchange in dichloro(organo)phosphane complexes 1a,b (R = CH(SiMe 3 ) 2 16 and Cp* 17 ) with t-BuLi at low temperature in the presence of 12-crown-4 ("12-c-4"). Reaction of 2 with the 1,3,2-dioxaphosphole derivative 3 14 yielded complexes 4a,b in diastereomeric ratios of ∼0.27 : 1 (4a,a′) and ∼0.33 : 1 (4b,b′) (Scheme 2).…”

Ambident Reactivity of Acetyl- and Formyl-Stabilized Phosphonium Ylides

“…Numerous publications on various aspects of Wittig chemistry have appeared in the recent chemical literature. Included among these are regio- and stereo­selective olefinations of keto-sugars, mechanistic and computational studies, , new methods for phosphonium salt and ylide generation, syntheses of metal-containing analogues of Wittig intermediates, , Wittig-type reactions of N -sulfonyl imines, new methods for byproduct separation, and syntheses of macrocycles, modified nucleosides, vinyl isocyanides, and novel Michael acceptors . Transition metal catalysis of Wittig reactions has become popular, with catalyzed production of ylide from a stoichiometric phosphorus source, , or of carbonyl reactant from a stoichiometric amount of alcohol .…”