Binaphthalene-2,2-dithiol

The cycloisomerization of 1,6-enynes can also be catalyzed enantioselectively using a Rh-BICP catalyst (eq 8). However, Rh-Me-DuPhos affords a significantly higher enantioselectivity than Rh-BICP for this process (Table 4). 

Analysis of Reagent Purity the presence of the disulfide can be checked by TLC on silica gel, eluting with dichloromethane. 

A single diastereoisomer is obtained in the reduction of the ketone with Lithium Aluminum Hydride as illustrated in eq 3. The addition of other nucleophiles such as methylmagnesium iodide also gives single adducts. 

Nucleophile (Nu) R Reaction conditions Diastereomeric ratio Yield (%) 

Monoxidation of the dithiepine gives single diastereomeric sulfoxides with pseudoequatorial configuration (eq 4). In general, the oxides exhibit increased diastereoselectivity with respect to the unoxidized substrates, as in the examples of eq 5.  

---

Carefully designed chiral auxiliaries, planned to fulfil specific requirements, find use in synthetic strategy. Such is the case of 1,1 -binaphthalene-2,2 -dithiol (3) prepared in enantiopure form [11,12]. 

The preparation of dibenzo-fused dithiepins was usually catalyzed by BF3 Et20. For example, the synthesis of dibenzo[7//][l,3]dithiepin from 1,1 -binaphthalene-2,2 -dithiol and dibromomethane and diiodomethane, respectively, failed however, reaction of the dithiol with dimethoxymethane in the presence of BF3-Et20 afforded the desired dithiepin in 71% yield <1995T787>. 

When both sulfinyl groups were incorporated into a cyclic structure, the di-enophilic reactivity was strongly improved, and the diastereoselectivity was dependent on the ring size. Thus, the first paper published dealt with the C2-symmetric ketendithioacetal S,S-dioxide 77 (Scheme 42, obtained from 1,1 -binaphthalene-2,2 -dithiol), which reacts with cyclopentadiene at room temperature over 12 h (milder conditions than those required by 75), yielding a 3 1 mixture of adducts [79]. The authors suggest a complete 7r-facial selectivity... 

Finally, it is notable that the title reagent has been used to prepare even larger ring systems such as chiral crown ethers, and the use of l,l -binaphthalene-2,2 -dithiol as ligand for rhodium(I) in the asymmetric hydroformylation of styrene has been described. ... 

Sulfur transfer. The reaction with arenediazonium salts leads to diaryl disulfides. Interestingly, l,l -binaphthalene-2,2 -dithiol is the only product (61% yield) in the reaction with the bis-diazonium salt derived from l,r-binaphthyl-2,2 -diamine. 

Ohtani showed that, as a result of the aurophilic character of the thiolate (RS ) function, R) and (5 )-l,l -binaphthalene-2,2 -dithiol (BNSH) (6.92) (Figure 6.68) attach themselves to the surface of Au (111) in a quasicovalent manner leading to the formation of a 2D phase with a rhombohedral structure. The configuration of this supramolecular arrangement of enantiopure molecules depends on the absolute configuration of the isolated molecule, being (C) for (5)-(BNSH) ( S)-(6.92) and (AC) for (/ )-(BNSH) (RH6.92). 

The Ti(0-i-Pr)4/(R,R)-DET (1 4) combination has been used for resolution of 2,2 -di-methylthio-[l,r-binaphthalene]. Through demethylation it is possible to recover both enantiomers of 2,2 -dithiol-[l,l -binaphthalene], a useful chiral auxiliary [59,60]. 

Reaction of dibromide 168 with l,T-binaphthalene-2,2 -bis(methylenethiol) 169 gave a mixture containing the disulfide 170 (17% based on 169), dinaphtho[2,l-f l, 2 -rf thiepine 23 (52% based on 169), and the major 171 isolated from reaction between dibromide 168 and dithiol 169 (41% based on 168) (Equation 25) <1995T787>. An efficient synthesis of thiepine 23 by treatment of dibromide 168 with sodium sulfide was also reported <1994JOC1326> (see Section 13.03.9.2). 

---