Alcohol ring-closing metathesis

The concept of performing microwave synthesis in room temperature ionic liquids (RTIL) as reaction media has been applied to several different organic transformations (Scheme 4.18), such as 1,3-dipolar cycloaddition reactions [54], catalytic transfer hydrogenations [55], ring-closing metathesis [56], the conversion of alcohols to alkyl halides [57, 58], and several others [59-61],... 

Another system for transfer vinylation has utilized [Ir(COD)Gl]2 as the catalyst, and was applicable to the preparation of vinyl ethers from the reactions of aliphatic alcohols with vinyl acetate (COD = 1,4-cyclooctadiene Scheme 4).117 This protocol has been used for the preparation of chromenes by a vinylation-ring-closing metathesis sequence (Equation (19)).118... 

It is interesting to note that the two reactions involving allyl acetate and the unprotected alcohol, but-3-en-l-ol, failed when the molybdenum catalyst was used. The failure of the Schrock catalyst to tolerate unprotected alcohols has also been observed in ring-closing metathesis [40], where a tertiary alcohol has proved to be the only success [41]. 

The ruthenium catalyst system, 14, shown in Fig. 3, also carries out ADMET condensation chemistry, albeit with higher concentrations being required to achieve reasonable reaction rates [32]. The possibility of intramolecular compl-exation with this catalyst influences the polymerization reaction, but nonetheless, ruthenium catalysis has proved to be a valuable contributor to overall condensation metathesis chemistry. Equally significant, these catalysts are tolerant to the presence of alcohol functionality [33] and are relatively easy to synthesize. For these reasons, ruthenium catalysis continues to be important in both ADMET and ring closing metathesis chemistry. 

A similar strategy has been employed in the synthesis of a dihydropyran required to achieve the synthesis of (—)-lanlimalide (Scheme 23). Thns, ally-lation of the secondary alcohol resnlting from a methallylation of 3-tri-n-butylstannylacrolein provided unsymmetrical ether 182, which is closed to a pyran with a ring-closing metathesis using Schrock s molybdennm catalyst. 

A novel approach to enantiopure spirocyclic (3-lactams has been developed by Alcaide et al. [106] using different intramolecular metal catalyzed cyclization reactions with monocyclic unsaturated alcohols 142 (Scheme 35). Ring-closing metathesis is one of the most powerful and reliable methods to construct a ring system. Transformation of alcohols in diolefin precursors followed by ring-closing... 

In addition, the bisallylation of the two secondary amides of compound 91, followed by treatment with an appropriate ruthenium catalyst, allowed a tandem ringopening metathesis/ring-closing metathesis to give, after alcohol deprotection, the quite complex structure 92 [82]. 

Seven-membered lactones can also be prepared in good yields by ruthenium-catalysed cyclocarbonylation of alkenyl alcohols (e.g. 119 from 118) [01TL5459] or by ring closing metathesis using Grubbs imidazolidine catalyst (e.g. 121 from 120, n=2) [02H85]. 

Ring-closing metathesis methodology has been used to access 7-membered ring sultones (e.g. 278, n = 1, m = 1) efficiently from the acyclic diene precursor 277, which could readily be made in turn fom the appropriate olefinic sulfonyl chloride and alcohol [02SL2019]. 

Endolytic glycosidases, 55 Esterification-ring-closing metathesis olefin alcohol esterification, 24,... 

The allyl alcohol linker 1.48 (106), bound to an aldehyde PS resin, has been elaborated to the pentenoic acid derivative shown. This was cyclized with cleavage using ring-closing metathesis (RCM) (Ru catalyst in DCE at 80 °C for 16 h) to give pure Freidinger lactam in solution. 

An alternative to ring-closing metathesis to access seven-membered rings has been described by Ohno et al. <03H(61)65>. Thus, reaction of the bromoallene 4 containing a nucleophilic moiety and Pd(PPh3)4 in the presence of methanol affords the azepine derivative 5 in good yield (76%). Oxepine derivatives can also be made in a similar way using an alcohol as the nucleophilic moiety in the allene. 

Ito et al. have reported that a sequence of intramolecular hydrosilylation or cya-nosilylation and the Pd-catalyzed coupling reaction is useful for regio- and stereo-defined synthesis of tri- or tetrasubstituted homoallyl alcohols from homopropargyl alcohols (Scheme 10.212) [551, 552]. More recently Denmark et al. have used ring-closing metathesis for the alkene synthesis via vinylsilanes [553]. 

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