Pempidine

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... 

Ganglion blocking (e.g. hexamethonium, pempidine) Blocked Normal Normal Not Yes... 

Subsequently, Bolm developed a variant of this process which employed just a sub-stoichiometric quantity of cinchona alkaloid [203], In this method, 10 mol% of quinidine was nsed in conjunction with a stoichiometric amount of pempidine to prevent seqnestration of the cinchona alkaloid by the acidic hemiester product. The chiral hemiester products derived from various meio-anhydrides were obtained with >74% ee and >94% yields (Table 9) [203],... 

Althongh both quinidine and pempidine can be recovered and rensed, it is noteworthy that pempidine is more expensive than qninidine and that this protocol reqnires very long reaction times. 

Ganglionic blocking agents (e.g., mecamylamine hydrochloride and pempidine)... 

Although both quinidine and pempidine can be quantitatively recovered and reused following these processes, it is noteworthy that pempidine is more expensive than quinidine. Moreover, the erosion in the levels of enantioselectivity observed in the hemiester products using the catalytic protocol relative to the stoichiometric protocol, as well as the extended reaction time, limit the utility of this modification. 

A noteworthy feature of the method is that turnover of the catalyst is achieved in the absence of a stoichiometric achiral base, despite the generation of an acidic product (cf. the use of pempidine in the Bolm catalytic protocol) [180-182]. The synthetic utility of this approach has been demonstrated in a formal total synthesis of (+)-biotin [183]. Recently a silica-supported heterogeneous analogue of (DHQD)2AQN has also been developed by Han [184, 185]. (For experimental details see Chapter 14.17.11). 

Infra-red Spectrum. Principal peaks at wavenumbers 1308,1261, 1210, 1136, 1063, 675 (pempidine tartrate, KBr disk). 

Hendry, I.A. (1973) Trans-synaptic regulation of tyrosine hydroxylase activity in a developing mouse sympathetic ganglion effect of nerve growth factor (NGF), NGF-antiserum and pempidine. Brain Re.s. 56 313-320. 

Such ganglionic blocking agents that interfere with the nervous transmission of sympathetic as well as para-sympathetic ganglia may include hexa-methonium bromide mecamylamine hydrochloride pempidine pentolinium tartrate, trimetaphan camsylate, etc. 

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