Intramolecular silylformylation alkynes

Intramolecular geometries, database studies, 1, 597 Intramolecular hydroalkoxylation, and etherification, 10, 672 Intramolecular pinacol coupling to cyclic 1,2-diols, 11, 51 with samarium reagents, 11, 60 Intramolecular silylformylation, alkynes and alkenes, 11, 489 Intramolecular solvomercuration alkenes, 2, 436 alkynes, 2, 439... 

Alkynes are viable substrates for the tandem intramolecular silylformylation/allylsilyla-tion reaction. The 1,5-diastereoselechvity is reversed from that observed with alkene substrates, as the 1,5-anti product predominates (Scheme 5.24) [38]. Synthetic flexibility was demonstrated in that either of two carbon-silicon cleavage procedures may be employed. Protodesilylahon with tetra-n-butylammonium fluoride followed by acetylation (determi-... 

A hydrosilyloxy moiety also works as a directing group for the intramolecular silylformylation regardless of terminal and internal alkynes (Table 9)7 ... 

A second example of intramolecular silylformylation involves reactions of terminal and internal alkynes linked to a dimethylsiloxy group, as depicted in Eq. (50).125... 

Tandem intramolecular silylformylation-allylation reaction of diallylhydrosilyl ethers derived from homoallyl alcohols is convenient for rapid, stereoselective synthesis of 1,3,5-triols convertible to more oxygen-functionalized compounds (Scheme 12).142,142a,142b 143 [ he second uncatalyzed allylation step would be facilitated by the formation of a strained silacycle intermediate, which has enough Lewis acidity to activate the formyl group. A similar tandem reaction via alkyne silylformylation has been reported.144... 

Although the reaction of 1-alkynes always affords 2-formyl products as shown in Eq. 66, this regiochemistry can be completely reversed using intramolecular silylformylation via exo-dig cyclization of alkynylsilanes and alkynyloxysi-... 

The silylformylation of 1-alkynes has been studied extensively affording (Z)-l-silyl-2-formyl-l-alkenes high regioselectivity. However, internal alkynes have not demonstrated high regioselectivity. Biffis et al. have reported using a cationic dirhodium(II) complex to achieve improved chemoselectivity for the silylformylation of internal alkynes.In addition, intramolecular silylformylation reactions were developed to aid in the regioselectivity of silylformylation of internal alkynes. ... 

Intramolecular cyclization is particularly effective to terminal alkynes containing three or four methylene units between acetylenic and silyl moieties such as 158, 160, and 162. But-3-ynylmethylphenylsilane does not give any positive result for CO incorporation. Regioselectivity for the silylformylation is completely reversed from the one in the standard silylformylation discussed in Section 11.14.2.2. A bulky /ft7-butyl group in 162 (R = Bu ) plays an... 

Although the regioselectivity for the silylformylation of 1-alkynes is excellent, that of internal alkynes is low except for 2-alkynoates (vide supra). Also, in the reactions of 1-alkynes, the silyl group is always delivered to the terminal position and the formyl to the C-2 position, thus it is impossible to synthesize 3-silyl-2-alkenals, which requires opposite regioselectivity. Intramolecular directed reactions can circumvent these limitations and expand the scope of the silylformylation of alkynes. 

Co2Rh2(CO)i2] and [Co3Rh(CO)i2] catalyze the hydrosilation of isoprene, cyclohexanone, cyclohexenone, and 1-alkynes, the regioseleetive inter- or intramolecular (Eq. 5) silylformylation of alkynes and 1-alkynals, and the silylcarbo-cyclization of enynes, diynes, and alkynals. These synthetically important reactions have been reviewed recently. 

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