Indolopyridine alkaloids

Takayama H et al. (2003) Gluco-indole alkaloids from Nauclea cadamba in Thailand and transformation of 3alpha-dihydrocadambine into the indolopyridine alkaloid, 16-carbomethoxynaufoline. Chem Pharm Bull (Tokyo) 51(2) 232-233... 

Numerous stannanes have been coupled with halopyridines as electrophiles in the Stille coupling. One of the simplest of these is vinylstannane [82-84]. The Stille reaction of bromopyridine 95 with tributylvinyltin gave angustine (96) [84], an indolopyridine alkaloid. Bromopyridine 95 also took part in a three-component carbonylative-Stille coupling sequence to provide an entry to another indolopyridine alkaloid, naucletine (97) [84]. 

An alternative route for installing a methyl ketone is the three component carbonylative-Stille coupling with tetramethyltin. An indolopyridine alkaloid, naucletine (58), was prepared using such a sequence from pyridyl bromide 57 <95CC1675>. 

Acid chlorides 21 and chloroformates 23 are the most commonly used activating agents and the preferred reagents for evaluating the reactivity of other components in new Reissert-type processes. For example, in studies on the total synthesis of the indolopyridine alkaloids 42, acetyl chloride was used in the key step to prepare the common synthetic intermediate 41. In this case, an enamide moiety intramole-cularly attacks the in situ generated Ai-acylazinium salt, and the Reissert adduct is spontaneously oxidized and hydrolyzed to regain aromaticity in the last step (Scheme 7) [44, 45]. 

Scheme 7 Synthesis of indolopyridine alkaloids based on a Reissert-type process...

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