To ensure high efficiency, turning a stoichiometric reaction into a catalytic one, and developing new catalytic reactions have been long-standing goals in modern synthesis. Ylide reactions are among the most powerful tools for constructing olefins [1] and small rings, [2] but few are catalytic, in particular those involving phosphorus ylides.[3] The first example of a catalytic Wittig-type reaction of arsenic ylides, in which a stoichiometric amount of reducing agent was used to regenerate the arsane, was described by Huang's group in 1989. [4] Afterwards, catalytic olefinations, epoxidations, aziridinations, and cyclopropanations of tellurium or sulfur ylides were accomplished. [2,5] Aggarwal's group developed catalytic, asymmetric ylide reactions that afforded three-membered rings by a carbene approach, in which the ylide was formed directly from aryl diazomethane in the presence of a catalytic amount of a chiral sulfide and a transition-metal complex. [6] To our knowledge, there are no phosphane-catalyzed versions of the carbon-phosphorus ylide reaction. [7] This might be due to the fact that, compared to other elemento-organic compounds of Groups 15 and 16, phosphanes exhibit higher oxyphilicity and the phosphorus-oxygen bond in phosphine oxides have a higher bond energy. To develop a catalytic reaction with carbon-phosphorus ylides, it was thus necessary to explore a new type of reaction.Two types of reactions of allylic phosphorus ylides A with electron-deficient alkenes have been reported (Scheme 1). The initial nucleophilic addition of the ylide to the olefin is followed by an intramolecular Wittig reaction to afford 1,3-cycloalkadienes [8a-f] or by intramolecular nucleophilic substitution to give cyclopropanes.[8f,g] However, both reactions are stoichiometric with regard to the phosphane and the products are obtained in low yields.The success of the phosphane-catalyzed isomerizations, aand g-additions, and [3þ2] cycloadditions of electron-deficient allenes or alkynes was ascribed to the presence of electron-withdrawing groups, which facilitated the nucleophilic additions and the elimination of phosphanes to complete the catalytic cycles. [9] With this in mind, we thought that phosphane-catalyzed reactions might be realized with a modified allylic phosphorus ylide B (see Scheme 1). Here we report a novel phosphane-catalyzed annulation reaction of modified allylic compounds with electron-deficient alkenes.To initiate our study, phosphonium salt 1, compound 2, and potassium carbonate were stirred in toluene at 90 8C to afford the adduct 3 a and triphenylphosphane [Eq. (1); E = CO 2 Et]. Since 1 was prepared from ethyl 2-bromomethyl-2-propenoate (4 a) and PPh 3 , it was expected that this reaction might take place starting from 4 a by utilizing a catalytic amount of PPh 3 . Indeed, the phosphane-catalyzed annulation Scheme 1. Two types of reactions of allylic phosphorus ylides.

A novel phosphine-catalyzed reaction of modified allylic compounds, including acetates, bromides, chlorides, or tert-butyl carbonates derived from the Morita-Baylis-Hillman (MBH) reaction with tropone to yield [3+6] annulation products in excellent yields was developed. It offers a simple and convenient method for constructing bridged nine-membered carbocycles.

A direct entry to spirocycles with low to moderate regioselectivity was achieved by triphenylphosphine-catalyzed [3 + 2]-cycloaddition of active exo-methylenecycles (1) and ethyl 2,3-butadienoate (2). The regioselectivity of the reaction was greatly improved by using the bulky tert-butyl ester of the 2,3-butadienoate (5). The regioselectivity of the reaction was further enhanced by using the tert-butyl 2-butynoate as the substrate. This protocol provided an efficient entry to the skeleton of spirocarbocycles, especially spiro[4.n]alkanes.