Condensation of ethyl and methyl 4-(triphenylphosphoranylidine)-3-oxobutanoate with enals

Six‐Membered Rings with One Oxygen: Pyrylium Ion, Related Systems and Benzo‐Derivatives

“…Several approaches have been devised for the preparation of the oxatriene precursor, such as the oxidation of dienols [72] or Wittig olefination [73]. In a recent approach, monocyclic functionalized 2H-pyrans 140 can be synthesized from propargyl vinyl ethers 137 (Scheme 18.42).…”

Preparation of Some Novel, Highly Unstable Chain Conjugated 2H‐Pyran‐5‐carboxylates

“…Condensation of conjugated unsaturated b-ketoesters 5a, 5b, 5c 13,14 with a,b-unsaturated aldehydes 3a and 3b gave the chain conjugated 2H-pyrans 1a, 7,8 1b, 1c 8 and 1d in a modest to good yield (Scheme III). The choice of base and solvent is very important.…”

“…1 2H-pyran-5-carboxylates have the unique ability to undergo reversible electrocyclic ring opening to the ketodiene valence isomer 2 making these compounds available for Michael attack (Scheme I). [3][4][5][6][7][8] Recently, we described the diverse products obtained from reactions of arsonium ylides with 2H-pyran-5-carboxylates. [3][4][5][6] The chain conjugated 2H-pyran ester 1a, showed chemoselectivity in condensations with ambident nucleophilic phosphonium ylides.…”

“…For example, only cyclohexenones or cyclohexadienes were isolated where both ester groups were attached to the ring system (Scheme I). [7][8][9] In this paper we describe the synthesis of highly unstable chain conjugated 2H-pyran esters 1.…”

Investigating the mechanism of 1,3,5-cycloheptatriene formation: Condensation of 1-methylethyl 3-oxo-4-(triphenylarsoranylidene)butanoate with 7-methoxy-3,7-dimethyloctanal

“…An aldol condensation of b-keto ester 3b with 10, followed by a Michael attack of the c-ylide of 1 (R 1 ‫ס‬Pr i ) on this aldol product, gives, after an intramolecular Wittig condensation, cyclohexenonedicarboxylate 11 [31,33].…”