Oxidation vinylstannanes

Three-component coupling with vinylstannane. norbornene (80). and bro-mobenzene affords the product 91 via oxidative addition, insertion, transme-tallation, and reductive elimination[85]. Asymmetric multipoint control in the formation of 94 and 95 in a ratio of 10 1 was achieved by diastereo-differ-entiative assembly of norbornene (80), the (5 )-(Z)-3-siloxyvinyl iodide 92 and the alkyne 93, showing that the control of four chiralities in 94 is possible by use of the single chirality of the iodide 92. The double bond in 92 should be Z no selectivity was observed with E form[86]. 

The a-bromo-7-lactone 901 undergoes smooth coupling with the acetonyltin reagent 902 to afford the o-acetonyl-7-butyrolactone 903[763j. The o-chloro ether 904, which has no possibility of //-elimination after oxidative addition, reacts with vinylstannane to give the allyl ether 905, The o -bromo ether 906 is also used for the intramolecular alkyne insertion and transmetallation with allylstannane to give 907[764],... 

The conversion of a thiolactone to a cyclic ether can also be used as a key step in the synthesis of functionalized, stereochemically complex oxacycles (see 64—>66, Scheme 13). Nucleophilic addition of the indicated higher order cuprate reagent to the C-S double bond in thiolactone 64 furnishes a tetrahedral thiolate ion which undergoes smooth conversion to didehydrooxepane 65 upon treatment with 1,4-diiodobutane and the non-nucleophilic base 1,2,2,6,6-pentamethylpiperidine (pempidine).27 Regio- and diastereoselective hydroboration of 65 then gives alcohol 66 in 89 % yield after oxidative workup. Versatile vinylstannanes can also be accessed from thiolactones.28 For example, treatment of bis(thiolactone) 67 with... 

Ni(cod)2 is an effective catalyst for the acylstannylation of allenes to give a wide range of a-(acylmethyl)vinylstannanes (Scheme 16.64) [70]. The catalytic reaction would be initiated by oxidative addition of an acylstannane to an Ni(0) complex to generate an acyl nickel complex. Addition of the acyl nickel complex to an allene would provide two possible intermediates leading to a-(acylmethyl)vinylstannanes. 

The stannylcupration of alkynes has been widely studied. Reaction of alkynes with lithium bis(tributylstannyl) cuprate leads to r -2-(tri butyl stannyl) vinyl cuprates, which are synthetically equivalent to cis- 1,2-ethylene dianions. Addition of the tin-copper reagent across the triple bond occurs i>7/-stereospecifically, thus providing Z-vinylstannanes. Phenylacetylene reacts with the tin cuprate with a regiochemistry opposite to that of 1-decyne.294 The intermediate cuprates react well with the various electrophiles.295 For example, the reaction with ethylene oxide gives primary alcohols, and further treatment of their />-toluenesulfonates with butyllithium gives 1-substituted cyclobutenes (Equation (120)) 294... 

In a similar manner to alkynes, arynes accept the addition of alkynylstannanes in the presence of a catalytic amount of a palladium-iminophosphine complex (Scheme 5.7.15). Here, a characteristic feature is the participation of a vinylstannane. The usual catalytic cycle (Scheme 5.7.16, left), starting with oxidative addition of a carbon-tin bond, is possible, but rather improbable, because there are no signs of oxidative addition of alkenylstannanes that can participate in the present carbostannylation. Consequently, the palladium(O) complex is likely to undergo oxidative cyclization with an aryne to form a palladacyclopropene (Scheme 5.7.16, right), which then reacts with an organostannane. 

The synthesis of the C1-C20 top segment 367 started with aldehyde 361 (Scheme 52). Addition of vinylstannane 362 to 361 gave a 1.3 1 mixture of the desired a-alcohol 363 and its P-isomer. The P-alcohol was transformed to the a-alcohol 363 by PDC oxidation followed by Corey asymmetric reduction using chiral oxaborolidine catalyst. After methylation of the alcohol, 363 led to aldehyde 364 through a standard procedure. Condensation of the dianion of A-acetylpipe-colic acid (365) with 364 followed by methylation and the Dess-Martin oxidation... 

Palladium-catalyzed hydrostannation of alkynes proceeds regio- and stereospecifically to afford the synthetically useful ( )-vinylstannanes. This reaction implies oxidative addition of RsSn—H to Pd(0) to generate a Pd(ll) hydrido stannyl intermediate, which then undergoes cis addition of the Pd—Sn bond to the alkyne bond, followed by reductive elimination of the ( )-vinylstannane. The supposed cis-PdCII) hydrido trialkylstannyl intermediates had so far remained elusive. Very recently, cis-PdCll) hydrido trialkylstannyl complexes have been synthesized for the first time. ... 

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