Bifunctionalized Allenes. Part XV. Synthesis of 2,5-dihydro-1,2-oxaphospholes by Electrophilic Cyclization Reaction of Phosphorylated α-Hydroxyallenes

Abstract

This paper discusses a reaction of phosphorylated α-hydroxyallenes with protected or unprotected hydroxy groups involving 5-endo-trig cyclizations. Various electrophilic reagents such as sulfuryl chloride, bromine, benzenesulfenyl and benzeneselenenyl chlorides have been applied. The paper describes the reaction of 1-hydroxyalkyl-1,2-dienephosphonates with electrophiles that produces 2-methoxy-2-oxo-2,5-dihydro-1,2-oxaphospholes due to the participation of the phosphonate neighbouring group in the cyclization. On the other hand, (1E)-alk-1-en-1-yl phosphine oxides were prepared as mixtures with 2,5-dihydro-1,2-oxaphosphol-2-ium halides in a ratio of about 1:2 by chemo-, regio, and stereoselective electrophilic addition to the C 2 -C 3 -double bond in the allene moiety and subsequent concurrent attack of the external (halide anion) and internal (phosphine oxide group) nucleophiles. The paper proposes a possible mechanism that involves cyclization and additional reactions of the phosphorylated α-hydroxyallenes.

Bifunctionalized allenes, Part XIX: Synthesis, electrophilic cyclization/addition, and coinage metal‐catalyzed cycloisomerization of phosphorylated 3‐(β‐hydroxy)allenes

“…Of particular interest are the applications of these groups as temporary transformers of chemical reactivity of the allenic system in the synthesis of eventually heterocyclic compounds. In a continuation to our previous reports on the synthesis and cyclization reactions of phosphorylated 1‐(α‐hydroxy)‐ and 1‐(β‐hydroxy)allenes as well as phosphorylated 3‐(α‐hydroxy)allenes, we have found a convenient and efficient method for regioselective synthesis of phosphorylated 3‐(β‐hydroxy)allenes by an atom economical [2,3]‐sigmatropic rearrangement of the mediated hydroxy‐substituted propargyl phosphite or phosphinite, which is to be used as starting materials in the electrophilic cyclization/addition and coinage metal‐catalyzed cycloisomerization reactions.…”

“…We started the present study with the reaction of the 3‐(β‐hydroxy)allenephosphonates with protected ( 5 ) or unprotected ( 8 ) hydroxy group with bromine or benzeneselenenyl chloride (Scheme ). We conducted the reactions under the optimized reaction conditions determined in the similar reactions of the phosphorylated 1‐(α‐hydroxy‐ and β‐hydroxy)allenes earlier—solvent CH 2 Cl 2 at −20°C using 1.0 equiv of the allenephosphonate and 1.2 equiv of the electrophilic reagent. We have to say that the reaction in the favor of 5‐ endo‐trig mode afforded the 2‐methoxy‐2‐oxo‐2,5‐dihydro‐1,2‐oxaphospholes 10a,b to have very good yields (79% and 72%) and it does not depend on the nature of the substituent on the hydroxy group, as a result of the neighboring group participation of phosphonate group in the cyclization.…”

“…In addition to the above‐mentioned preparation of 2,5‐dihydro‐1,2‐oxaphospholes by electrophilic cyclization of the 3‐(β‐hydroxymethyl)‐allenephosphonates 5 and 8 due to the participation of the phosphonate neighboring group in the 5‐ endo‐trig cyclization, the next step in our study was to explore the possibilities of the cycloisomerization reaction of the above phosphorylated 3‐(β‐hydroxy)allenes 8 and 9 in the presence of coinage metal salts as catalysts. We conducted the reaction under the optimized reaction conditions determined in the similar reactions of the phosphorylated 1‐(α‐hydroxy)‐ and 1‐(β‐hydroxy)‐allenes earlier—solvent methylene chloride, 5 mol % catalyst and room temperature. The reaction occurred via an 6‐ endo‐trig cyclization to give the 2‐phosphoryl‐5,6‐dihydro‐2 H ‐pyrans 12a,b (Scheme ).…”

Fifty Years of (Benz)oxaphospholene Chemistry

“…[55] When unsubstituted 1,2-propadienylphosphonatesw ere treated with bromine, electrophilic addition of the dihalogent ook place instead of cyclization, probably because of the lack of stabilization of the halonium intermediate. [64][65][66][67] Later,w hen other synthetic entriest oa llenylphosphonates were found, the cyclization reaction of these allenylphosphonates with dihalogens remained an attractive strategy to afford oxaphospholenes. [55] Vinyl, allyl, benzyl, and propargyl substituents werew ell tolerated in this electrophilic addition/cyclization step, [56,61,62] whileallenylphosphonatesc arrying ac yclohexylg roup produced spirocyclic oxaphospholenes.…”

“…[63] Soon, this two-step strategy becamet he method of choice to prepareo xaphospholenes 88. [64][65][66][67] Later,w hen other synthetic entriest oa llenylphosphonates were found, the cyclization reaction of these allenylphosphonates with dihalogens remained an attractive strategy to afford oxaphospholenes. [68] Oxaphospholenes with a3 -phenylthio-, [56] 3-phenylseleno, [56] 3-hydroxymethyl, [69] 3-fluoromethyl, [70] or an extra 3-halo-substituent [71] could be synthesized from the appropriately functionalized allenylphosphonates.…”