Mikoyan-Gurevich I-370

In 1953, Mikoyan OKB completed a design of a single-engined tactical fighter which used a wing similar to that of the twin-engined SM-9, which was the prototype and most direct forerunner of the MiG-19, whose work was proceeding in parallel.
It was officially designated as I-370 and received the internal OKB name of 'I-1'. It was powered by a single Klimov VK-7 rated with a thrust power of 3.525 kg (7771,295 lb) and boosted to 5.235 kg (11.541,2 lb) with afterburner.
The prototype took off to the skies for the first time on 16th February 1955, but high speed manoeuvring was disappointing. Consequently, it was returned to the Moscow Air Factory No.155 (Mikoyan-Gurevich's factory) to have installed an uprated VK-7 engine with a normal thrust power of 3.935 kg (8675,19 lb) and 6.270 kg (13.822,98 lb) of afterburner thrust power. This new prototype, which received the internal designation of 'I-2', received a new wing, with the quarter-chord sweptback increased from 55 degrees, from the original one, to 57 degrees of the new one.
Testing of the second prototype was limited as it was realised that the design didn't allow to attain the maximum expected speed.
A further development was expected, the I-380, with some designs and fuselages completed, but its expected engine, a more powerful Klimov VK-3 engine was never delivered.

Sources:
1. http://www.aviastar.org/air/russia/mig_i-370.php
2. https://www.valka.cz/topic/view/782
3. http://ram-home.com/ram-old/i-1mikoy.html
4. Salamander Books - The Complete Book of Fighters