Cyclization, 1,1 -binaphthyl

The principal variations on the normal crown synthesis methods were applied in preparing mixed crowns such as those shown in Eq. (3.55) and in forming isomers of the dibinaphthyl-22-crown-6 systems. The latter has been discussed in Sect. 3.5 (see Eq. 3.21) . The binaphthyl unit was prepared to receive a non-naphthyl unit as shown in Eq. (3.57). Binaphthol was allowed to react with the tetrahydropyranyl ether or 2-chloroethoxyethanol. Cleavage of the THP protecting group followed by tosyla-tion of the free hydroxyl afforded a two-armed binaphthyl unit which could serve as an electrophile in the cyclization with catechol. Obviously, the reaction could be accomplished in the opposite direction, beginning with catechol". ... 

A series of chiral binaphthyl ligands in combination with AlMe3 has been used for the cycloaddition reaction of enamide aldehydes with Danishefsky s diene for the enantioselective synthesis of a chiral amino dihydroxy molecule [15]. The cycloaddition reaction, which was found to proceed via a Mukaiyama aldol condensation followed by a cyclization, gives the cycloaddition product in up to 60% yield and 78% ee. 

Wacker cyclization has proved to be one of the most versatile methods for functionalization of olefins.58,59 However, asymmetric oxidative reaction with palladium(II) species has received only scant attention. Using chiral ligand 1,1 -binaphthyl-2,2 -bis(oxazoline)-coordinated Pd(II) as the catalyst, high enantioselectivity (up to 97% ee) has been attained in the Wacker-type cyclization of o-alkylphenols (66a-f) (Scheme 8-24). 

Enantioselective carbonylative cyclization has been realized with o-alkenylaryl triflates in the presence of 2,2-bis(diphenyl-phosphanyl)-1,1-binaphthyl (BINAP) or TolBINAP ligands in high material yields and enantiomeric excess (Equation (41)). ... 

Asymmetric cyclization of nerol and famesol.1 A biomimetic cyclization of nerol to limonene can be effected with an aluminum reagent 2 and a chiral leaving group. Thus the neryl ether 3 of R-( + )-2,2 -dihydroxy-1,1 -binaphthyl is cyclized... 

The only examples of carbocyclic products arising from cyclizations subsequent to Srn 1 reactions, are the isolated example reported by Bunnett and Singh,94 which gives products (18H20 Section 2.2.2.4.2) and the recently reported synthesis of unsymmetrically hydroxylated 2,2 -binaphthyls.114 The final pro-... 

A phenolic oxygen participates in facile oxypalladation. 2-Allylphenol (55) undergoes clean cyclization to 2H-l-benzopyran (56) in DMSO under air with a catalytic amount of Pd(OAc)2 without a reoxidant. 2-Methylbenzofuran (57) is obtained when PdCl2 is used [50]. But different chemoselectivity with the Pd(II) salts was also reported [51]. Catalytic asymmetric cyclization of the tetrasubstituted 2-allylic phenol 58 using the binaphthyl-type chiral ligand 60, called (.S, .S )-ip-borax, afforded the furan 59 with 96% ee. Use of Pd(CF3 002)2 as a catalyst is essential in the presence of benzoquinone [52]. Formation of the benzofuran 62 from 61 has been utilized in the synthesis of aklavinione [53]. The intramolecular reaction of 2-hydroxychalcone (63) produces the flavone 64 [54]. 

Chiral oxa-thiacrown ethers containing a l,l -binaphthyl unit have been prepared by Stock and Kellogg <1996JOC3093>. To prepare 42, they used either the bis-mesylate or dibromide (Scheme 8) however, changing the leaving group did not help improve the yields of cyclization products. 

A Pd-catalyzed oxidative cyclization of phenols with oxygen as stoichiometric oxidant in the noncoordinating solvent toluene has been developed for the synthesis of dihydrobenzo[ ]furans (Equation 136). Asymmetric variants of this Wacker-type cyclization have been reported by Hayashi and co-workers employing cationic palladium/2,2 -bis(oxazolin-2-yl)-l,l -binaphthyl (boxax) complexes <1998JOC5071>. Stoltz and co-workers have reported ee s of up to 90% when (—)-sparteine is used as a chiral base instead of pyridine <2003AGE2892, 2005JA17778>. Attempts to effect such a heteroatom cyclization with primary alcohols as substrates, on the other hand, led to product mixtures contaminated with aldehydes and alkene isomers, which is in contrast to the reactions with the Pd(ii)/02 system in DMSO <1995TL7749>. 

One successful approach for the selective formation of conformationally well-defined -symmetric -metallocenes has been the use of bis-aryl or binaphthyl bridges to link Gp or Ind ligands. Another approach has been to use doubly bridged bis-Cp ligands. A third methodology implies the application of the Nazarov cyclization for the preparation of rigid doubly bridged bis-indene compounds which lead to -symmetric -metallocenes. 

Uozumi developed polymer-supported 2,2 -bis(oxazolin-2-yl)-l,l -binaphthyls 252 as chiral ligands for the asymmetric Wacker-type cyclization reaction (Scheme 3.81) [152]. In the presence ofthe polymeric catalyst derived from [Pd(MeCN)4](BF4)2] and 252 o-allylphenol, 253 was asymmetrically cychzed to give 254 in 46% yield with 95% ee. 

Other miscellaneous cyclization reactions leading to interesting thiophene derivatives include a thermal conversion of a 2,2 -bis(A/,Af-dimethylthiocarbamoyloxy)-1,1 -binaphthyl into a dinaphtho[2,l-6 l, 2 -t/ thiophene (a heterohelicene) <0581109>, solution-phase parallel synthesis of a 1140-member ureidothiophene earboxylic acid hbrary <05JCC253>, and an unexpected cyclization occurring upon metalation of diphenylsulfone, followed by introduction of (-)-fenchone and subsequent aqueous workup <05T10449>. Heating of the... 

One of the exciting developments of the Wacker-type oxidation is the asymmetric synthesis of the reaction. For instance, using a new chiral bis(oxazoline) ligand L = 3,3 -Disubstituted 2,2 -bis(oxazolyl)-l,r-binaphthyls (boxax), a catalytic asymmetric Wacker -type cyclization converted allyl-phenol 55 to dihydrofuran 74 with 67% ee.ss... 

In the first assignment of absolute configuration to a helicene, the bisphosphonium periodate (118), obtained from the binaphthyl (117) of known absolute configuration, reacted with base to give (+ )-(P)-penta-helicene (119). Wittig reactions have also been used to obtain the stilbenes required for photochemical cyclization to give [8]helicene, and a [6]helicene of known absolute configuration. ... 

The attachment of a R3Si (31) or an biphenylyl (30) group enhances the electron affinity of a benzene ring. Such substitution permits biphenyl rings (33) or the triphenylene system (32) to be generated readily. Collateral evidence in support of radical-anionic intermediates in these reactions has been obtained (5). Another example of the intramolecular cyclization is the formation of perylene from 1,1 -binaphthyl. 

Binaphthyl-bisoxazoline ligands (the so-called boxax) [165,166] have also been immobilized on various polymer supports [167]. A palladium complex of polymeric boxax 116 catalyzed the Wacker-type cyclization [168, 169] of al-lylphenol 117 with up to 96% ee (Scheme 38) [170]. 

Asymmetric carbonyl-ene cyclization of alkenyloxy-substituted aldehydes <9ITL6571> afforded six- and seven-membered cyclic ethers of high enantiomeric purity, for example (/ )-(30) possessed a 91% ee (Equation (10)), when chiral 2,2 -dihydroxy-l,r-binaphthyl-based titanium perchlorate was used as a catalyst. 

Pd(0Ac)2, but the benzofuran 67 was obtained by exo cyclizadon with PdCb [34], Catalytic asymmetric cyclization of 2-(2,3-dimethyl-2-butenyl)phenol (68) using the binaphthyl-based chiral ligand 70, called (5,5)-ip-boxax afforded the furan 69 with high ee (97%) [35],... 

Preparation of cyclic ethers by intramolecular reactions of the primary (29 and 33) and the secondary alcohols (31 and 35) proceeds more easily using CS2CO3 or K3PO4, and binaphthyl-based monophosphine ligands VI-1, VI-9 [9], The five-, six-, and seven-membered cyclic ethers 30, 32, and 34 were prepared from the aryl chloride 31 and bromides 29 and 33. The benzoxazapine 36 was obtained without racemization of chiral alcohol by the cyclization of the optically active bromo alcohol 35. 

A variety of chiral phosphine ligands have been used to promote asymmetric Mizoroki-Heck reactions (17-26, Figure 16.1). To date, 2,2 -bis(diphenylphosphino)-l,F-binaphthyl (BINAP 17) has been employed most widely it is often employed for first testing a new asymmetric Mizoroki-Heck cyclization. However, an empirical approach typically is required for determining the optimal ligand for a given reaction. There are... 

Allylpalladium complexes with BOX-type ligands and glucopyrano-oxazoline-palladium catalysts were used as catalysts for enantioselective allylic substitution (277). A chiral bisoxazoline ligand (BOXBZ) developed by Pfaltz has been used for asymmetric carbo- and heteroannulation reactions (278). An axial binaphthyl-based ligand possessing oxazolyl substituents (BOXAX) was developed by Hayashi and co-workers and successfully applied for the asymmetric Wacker-type cyclization (279). 

Sekar and co-workers found that by combining CUCI2 with l,l -binaphthyl-2,2 -diamine in MeCN with CS2CO3 as a base, M-(2-chlorophenyl)-benzothioamides can be cyclized at 82-110 Moderate to excellent... 

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